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NAME

       bash - GNU Bourne-Again SHell

SYNOPSIS

       bash [options] [command_string | file]

COPYRIGHT

       Bash is Copyright (C) 1989-2022 by the Free Software Foundation, Inc.

DESCRIPTION

       Bash is an sh-compatible command language interpreter that executes commands read from the
       standard input or from a file.  Bash also incorporates useful features from the Korn and C
       shells (ksh and csh).

       Bash  is  intended to be a conformant implementation of the Shell and Utilities portion of
       the IEEE POSIX specification (IEEE Standard 1003.1).  Bash can be configured to be  POSIX-
       conformant by default.

OPTIONS

       All of the single-character shell options documented in the description of the set builtin
       command, including -o, can be used as options when the shell  is  invoked.   In  addition,
       bash interprets the following options when it is invoked:

       -c        If  the  -c  option is present, then commands are read from the first non-option
                 argument command_string.  If there are arguments after the  command_string,  the
                 first argument is assigned to $0 and any remaining arguments are assigned to the
                 positional parameters.  The assignment to $0 sets the name of the  shell,  which
                 is used in warning and error messages.
       -i        If the -i option is present, the shell is interactive.
       -l        Make bash act as if it had been invoked as a login shell (see INVOCATION below).
       -r        If  the -r option is present, the shell becomes restricted (see RESTRICTED SHELL
                 below).
       -s        If the -s option is present, or if no arguments remain after option  processing,
                 then  commands  are  read  from  the  standard  input.   This  option allows the
                 positional parameters to be set when  invoking  an  interactive  shell  or  when
                 reading input through a pipe.
       -v        Print shell input lines as they are read.
       -x        Print commands and their arguments as they are executed.
       -D        A  list  of  all  double-quoted strings preceded by $ is printed on the standard
                 output.  These are the strings that are subject to language translation when the
                 current  locale is not C or POSIX.  This implies the -n option; no commands will
                 be executed.
       [-+]O [shopt_option]
                 shopt_option is one of the shell options accepted  by  the  shopt  builtin  (see
                 SHELL BUILTIN COMMANDS below).  If shopt_option is present, -O sets the value of
                 that option; +O unsets it.  If shopt_option  is  not  supplied,  the  names  and
                 values  of  the  shell  options  accepted  by  shopt are printed on the standard
                 output.  If the invocation option is +O, the output is  displayed  in  a  format
                 that may be reused as input.
       --        A  --  signals  the  end of options and disables further option processing.  Any
                 arguments after the -- are treated as filenames and arguments.  An argument of -
                 is equivalent to --.

       Bash  also  interprets  a number of multi-character options.  These options must appear on
       the command line before the single-character options to be recognized.

       --debugger
              Arrange for the debugger profile to be executed before the shell starts.  Turns  on
              extended  debugging  mode  (see the description of the extdebug option to the shopt
              builtin below).
       --dump-po-strings
              Equivalent to -D, but the output is in the GNU gettext po  (portable  object)  file
              format.
       --dump-strings
              Equivalent to -D.
       --help Display a usage message on standard output and exit successfully.
       --init-file file
       --rcfile file
              Execute  commands  from  file  instead  of  the  system  wide  initialization  file
              /etc/bash.bashrc and the standard personal initialization  file  ~/.bashrc  if  the
              shell is interactive (see INVOCATION below).

       --login
              Equivalent to -l.

       --noediting
              Do  not  use  the  GNU  readline  library  to  read command lines when the shell is
              interactive.

       --noprofile
              Do not read either the system-wide startup file /etc/profile or any of the personal
              initialization  files  ~/.bash_profile,  ~/.bash_login, or ~/.profile.  By default,
              bash reads these files when it is invoked as a login shell (see INVOCATION below).

       --norc Do not read and execute the system wide initialization  file  /etc/bash.bashrc  and
              the  personal  initialization  file  ~/.bashrc  if  the shell is interactive.  This
              option is on by default if the shell is invoked as sh.

       --posix
              Change the behavior of bash where the default  operation  differs  from  the  POSIX
              standard to match the standard (posix mode).  See SEE ALSO below for a reference to
              a document that details how posix mode affects bash's behavior.

       --restricted
              The shell becomes restricted (see RESTRICTED SHELL below).

       --verbose
              Equivalent to -v.

       --version
              Show version information for this instance of bash on the standard output and  exit
              successfully.

ARGUMENTS

       If arguments remain after option processing, and neither the -c nor the -s option has been
       supplied, the first argument is assumed  to  be  the  name  of  a  file  containing  shell
       commands.   If bash is invoked in this fashion, $0 is set to the name of the file, and the
       positional parameters are set  to  the  remaining  arguments.   Bash  reads  and  executes
       commands  from  this  file, then exits.  Bash's exit status is the exit status of the last
       command executed in the script.  If no commands are executed, the exit status  is  0.   An
       attempt is first made to open the file in the current directory, and, if no file is found,
       then the shell searches the directories in PATH for the script.

INVOCATION

       A login shell is one whose first character of argument zero is a -, or  one  started  with
       the --login option.

       An  interactive shell is one started without non-option arguments (unless -s is specified)
       and without the -c option, whose standard input and error are both connected to  terminals
       (as  determined  by  isatty(3)),  or  one  started  with the -i option.  PS1 is set and $-
       includes i if bash is interactive, allowing a shell script or a startup file to test  this
       state.

       The  following  paragraphs  describe  how  bash executes its startup files.  If any of the
       files exist but cannot be read, bash reports an error.  Tildes are expanded  in  filenames
       as described below under Tilde Expansion in the EXPANSION section.

       When bash is invoked as an interactive login shell, or as a non-interactive shell with the
       --login option, it first reads and executes commands from the file /etc/profile,  if  that
       file  exists.   After  reading that file, it looks for ~/.bash_profile, ~/.bash_login, and
       ~/.profile, in that order, and reads and executes commands from the first one that  exists
       and  is readable.  The --noprofile option may be used when the shell is started to inhibit
       this behavior.

       When an interactive login shell exits, or a non-interactive login shell executes the  exit
       builtin  command,  bash  reads  and  executes commands from the file ~/.bash_logout, if it
       exists.

       When an interactive shell that is not a login shell is started, bash  reads  and  executes
       commands from /etc/bash.bashrc and ~/.bashrc, if these files exist.  This may be inhibited
       by using the --norc option.  The --rcfile file option will force bash to read and  execute
       commands from file instead of /etc/bash.bashrc and ~/.bashrc.

       When  bash  is started non-interactively, to run a shell script, for example, it looks for
       the variable BASH_ENV in the environment, expands its value if it appears there, and  uses
       the  expanded  value  as  the  name of a file to read and execute.  Bash behaves as if the
       following command were executed:
              if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
       but the value of the PATH variable is not used to search for the filename.

       If bash is invoked with the name sh, it tries to mimic the startup behavior of  historical
       versions  of  sh  as  closely as possible, while conforming to the POSIX standard as well.
       When invoked as an interactive login shell, or a non-interactive shell  with  the  --login
       option,  it  first attempts to read and execute commands from /etc/profile and ~/.profile,
       in that order.  The --noprofile option may be used to inhibit this behavior.  When invoked
       as  an  interactive  shell  with the name sh, bash looks for the variable ENV, expands its
       value if it is defined, and uses the expanded value as the name of  a  file  to  read  and
       execute.   Since  a shell invoked as sh does not attempt to read and execute commands from
       any other startup files, the --rcfile option  has  no  effect.   A  non-interactive  shell
       invoked  with  the name sh does not attempt to read any other startup files.  When invoked
       as sh, bash enters posix mode after the startup files are read.

       When bash is started in posix mode, as with the --posix command line  option,  it  follows
       the  POSIX  standard  for  startup files.  In this mode, interactive shells expand the ENV
       variable and commands are read and executed from the  file  whose  name  is  the  expanded
       value.  No other startup files are read.

       Bash  attempts  to  determine  when it is being run with its standard input connected to a
       network connection, as when executed by the historical remote shell daemon, usually  rshd,
       or  the secure shell daemon sshd.  If bash determines it is being run non-interactively in
       this fashion, it reads and executes commands from /etc/bash.bashrc and ~/.bashrc, if these
       files  exist  and  are readable.  It will not do this if invoked as sh.  The --norc option
       may be used to inhibit this behavior, and the --rcfile option may be used to force another
       file  to  be read, but neither rshd nor sshd generally invoke the shell with those options
       or allow them to be specified.

       If the shell is started with the effective user (group) id not  equal  to  the  real  user
       (group)  id, and the -p option is not supplied, no startup files are read, shell functions
       are not inherited from the environment, the SHELLOPTS, BASHOPTS,  CDPATH,  and  GLOBIGNORE
       variables,  if  they  appear in the environment, are ignored, and the effective user id is
       set to the real user id.  If the -p option is supplied at invocation, the startup behavior
       is the same, but the effective user id is not reset.

DEFINITIONS

       The following definitions are used throughout the rest of this document.
       blank  A space or tab.
       word   A sequence of characters considered as a single unit by the shell.  Also known as a
              token.
       name   A word consisting only of alphanumeric characters and  underscores,  and  beginning
              with an alphabetic character or an underscore.  Also referred to as an identifier.
       metacharacter
              A character that, when unquoted, separates words.  One of the following:
              |  & ; ( ) < > space tab newline
       control operator
              A token that performs a control function.  It is one of the following symbols:
              || & && ; ;; ;& ;;& ( ) | |& <newline>

RESERVED WORDS

       Reserved  words  are  words that have a special meaning to the shell.  The following words
       are recognized as reserved when unquoted and either the first word of a command (see SHELL
       GRAMMAR  below),  the  third  word  of a case or select command (only in is valid), or the
       third word of a for command (only in and do are valid):

       ! case  coproc  do done elif else esac fi for function if in select then until while  {  }
       time [[ ]]

SHELL GRAMMAR

       This section describes the syntax of the various forms of shell commands.

   Simple Commands
       A  simple  command  is  a  sequence  of  optional  variable assignments followed by blank-
       separated words and redirections, and terminated by a control operator.   The  first  word
       specifies the command to be executed, and is passed as argument zero.  The remaining words
       are passed as arguments to the invoked command.

       The return value of a simple command is its exit  status,  or  128+n  if  the  command  is
       terminated by signal n.

   Pipelines
       A pipeline is a sequence of one or more commands separated by one of the control operators
       | or |&.  The format for a pipeline is:

              [time [-p]] [ ! ] command1 [ [||&] command2 ... ]

       The standard output of command1 is connected via a pipe to the standard input of command2.
       This  connection  is  performed  before  any  redirections  specified  by the command1(see
       REDIRECTION below).  If |& is used, command1's standard error, in addition to its standard
       output,  is  connected  to command2's standard input through the pipe; it is shorthand for
       2>&1 |.  This implicit redirection of  the  standard  error  to  the  standard  output  is
       performed after any redirections specified by command1.

       The  return  status  of  a  pipeline  is  the  exit status of the last command, unless the
       pipefail option is enabled.  If pipefail is enabled, the pipeline's return status  is  the
       value  of  the  last  (rightmost)  command  to exit with a non-zero status, or zero if all
       commands exit successfully.  If the reserved word !  precedes a pipeline, the exit  status
       of that pipeline is the logical negation of the exit status as described above.  The shell
       waits for all commands in the pipeline to terminate before returning a value.

       If the time reserved word precedes a pipeline, the elapsed as well as user and system time
       consumed  by  its  execution  are  reported  when  the pipeline terminates.  The -p option
       changes the output format to that specified by POSIX.  When the shell is in posix mode, it
       does  not  recognize  time  as  a  reserved word if the next token begins with a `-'.  The
       TIMEFORMAT variable may  be  set  to  a  format  string  that  specifies  how  the  timing
       information  should  be displayed; see the description of TIMEFORMAT under Shell Variables
       below.

       When the shell is in posix mode, time may be followed by a newline.   In  this  case,  the
       shell displays the total user and system time consumed by the shell and its children.  The
       TIMEFORMAT variable may be used to specify the format of the time information.

       Each command in a multi-command pipeline, where  pipes  are  created,  is  executed  in  a
       subshell,  which  is  a  separate  process.   See  COMMAND  EXECUTION  ENVIRONMENT  for  a
       description of subshells and a subshell environment.  If the lastpipe  option  is  enabled
       using  the  shopt  builtin  (see  the  description  of shopt below), the last element of a
       pipeline may be run by the shell process when job control is not active.

   Lists
       A list is a sequence of one or more pipelines separated by one of the operators ;, &,  &&,
       or ||, and optionally terminated by one of ;, &, or <newline>.

       Of  these list operators, && and || have equal precedence, followed by ; and &, which have
       equal precedence.

       A sequence of one or more newlines may appear in a list instead of a semicolon to  delimit
       commands.

       If  a  command  is terminated by the control operator &, the shell executes the command in
       the background in a subshell.  The shell does not wait for the command to finish, and  the
       return  status  is 0.  These are referred to as asynchronous commands.  Commands separated
       by a ; are executed sequentially; the shell waits for each command to terminate  in  turn.
       The return status is the exit status of the last command executed.

       AND and OR lists are sequences of one or more pipelines separated by the && and || control
       operators, respectively.  AND and OR lists are executed with left associativity.   An  AND
       list has the form

              command1 && command2

       command2 is executed if, and only if, command1 returns an exit status of zero (success).

       An OR list has the form

              command1 || command2

       command2 is executed if, and only if, command1 returns a non-zero exit status.  The return
       status of AND and OR lists is the exit status of the last command executed in the list.

   Compound Commands
       A compound command is one of  the  following.   In  most  cases  a  list  in  a  command's
       description may be separated from the rest of the command by one or more newlines, and may
       be followed by a newline in place of a semicolon.

       (list) list is executed in a subshell (see  COMMAND  EXECUTION  ENVIRONMENT  below  for  a
              description  of a subshell environment).  Variable assignments and builtin commands
              that affect the shell's environment do not  remain  in  effect  after  the  command
              completes.  The return status is the exit status of list.

       { list; }
              list  is simply executed in the current shell environment.  list must be terminated
              with a newline or semicolon.  This is known as a group command.  The return  status
              is  the  exit status of list.  Note that unlike the metacharacters ( and ), { and }
              are reserved words and must  occur  where  a  reserved  word  is  permitted  to  be
              recognized.  Since they do not cause a word break, they must be separated from list
              by whitespace or another shell metacharacter.

       ((expression))
              The expression is evaluated according to the rules described below under ARITHMETIC
              EVALUATION.   If  the  value of the expression is non-zero, the return status is 0;
              otherwise the return status is 1.  The expression undergoes the same expansions  as
              if  it were within double quotes, but double quote characters in expression are not
              treated specially and are removed.

       [[ expression ]]
              Return a status of 0 or 1 depending on the evaluation of the conditional expression
              expression.   Expressions  are  composed  of  the  primaries  described below under
              CONDITIONAL EXPRESSIONS.  The words between the [[  and  ]]  do  not  undergo  word
              splitting  and  pathname  expansion.  The shell performs tilde expansion, parameter
              and  variable  expansion,  arithmetic  expansion,  command  substitution,   process
              substitution,  and quote removal on those words (the expansions that would occur if
              the words were enclosed in double quotes).  Conditional operators such as  -f  must
              be unquoted to be recognized as primaries.

              When  used  with [[, the < and > operators sort lexicographically using the current
              locale.

       See the description of the test builtin command (section SHELL BUILTIN COMMANDS below) for
       the handling of parameters (i.e.  missing parameters).

       When  the  ==  and  !=  operators  are  used,  the  string to the right of the operator is
       considered a pattern and matched according to the  rules  described  below  under  Pattern
       Matching,  as  if  the extglob shell option were enabled.  The = operator is equivalent to
       ==.  If the nocasematch shell option is enabled, the match is performed without regard  to
       the  case  of  alphabetic characters.  The return value is 0 if the string matches (==) or
       does not match (!=) the pattern, and 1 otherwise.  Any part of the pattern may  be  quoted
       to force the quoted portion to be matched as a string.

       An  additional  binary  operator, =~, is available, with the same precedence as == and !=.
       When it is used, the string to the right of the operator is considered  a  POSIX  extended
       regular expression and matched accordingly (using the POSIX regcomp and regexec interfaces
       usually described in regex(3)).  The return value is 0 if the string matches the  pattern,
       and  1  otherwise.   If the regular expression is syntactically incorrect, the conditional
       expression's return value is 2.  If the nocasematch shell option is enabled, the match  is
       performed without regard to the case of alphabetic characters.  If any part of the pattern
       is quoted, the quoted portion is matched literally.  This means  every  character  in  the
       quoted portion matches itself, instead of having any special pattern matching meaning.  If
       the pattern is stored in a shell variable,  quoting  the  variable  expansion  forces  the
       entire  pattern to be matched literally.  Treat bracket expressions in regular expressions
       carefully, since normal  quoting  and  pattern  characters  lose  their  meanings  between
       brackets.

       The pattern will match if it matches any part of the string.  Anchor the pattern using the
       ^ and $ regular expression operators to force it to match the entire  string.   The  array
       variable  BASH_REMATCH records which parts of the string matched the pattern.  The element
       of BASH_REMATCH with index 0 contains the  portion  of  the  string  matching  the  entire
       regular expression.  Substrings matched by parenthesized subexpressions within the regular
       expression are saved in the remaining BASH_REMATCH indices. The  element  of  BASH_REMATCH
       with  index  n  is the portion of the string matching the nth parenthesized subexpression.
       Bash sets BASH_REMATCH in the global scope; declaring it as a local variable will lead  to
       unexpected results.

       Expressions  may  be combined using the following operators, listed in decreasing order of
       precedence:

              ( expression )
                     Returns the value of expression.  This may be used to  override  the  normal
                     precedence of operators.
              ! expression
                     True if expression is false.
              expression1 && expression2
                     True if both expression1 and expression2 are true.
              expression1 || expression2
                     True if either expression1 or expression2 is true.

              The  && and || operators do not evaluate expression2 if the value of expression1 is
              sufficient to determine the return value of the entire conditional expression.

       for name [ [ in [ word ... ] ] ; ] do list ; done
              The list of words following in is  expanded,  generating  a  list  of  items.   The
              variable  name  is  set  to each element of this list in turn, and list is executed
              each time.  If the in word is omitted, the for command executes list once for  each
              positional  parameter that is set (see PARAMETERS below).  The return status is the
              exit status of the last command that executes.   If  the  expansion  of  the  items
              following  in  results  in  an empty list, no commands are executed, and the return
              status is 0.

       for (( expr1 ; expr2 ; expr3 )) ; do list ; done
              First, the  arithmetic  expression  expr1  is  evaluated  according  to  the  rules
              described  below  under  ARITHMETIC EVALUATION.  The arithmetic expression expr2 is
              then evaluated repeatedly until it evaluates to zero.  Each time expr2 evaluates to
              a  non-zero  value,  list  is  executed  and  the  arithmetic  expression  expr3 is
              evaluated.  If any expression is omitted, it behaves as if it evaluates to 1.   The
              return  value  is  the exit status of the last command in list that is executed, or
              false if any of the expressions is invalid.

       select name [ in word ] ; do list ; done
              The list of words following in is expanded, generating a list of items, and the set
              of  expanded words is printed on the standard error, each preceded by a number.  If
              the in word is omitted, the  positional  parameters  are  printed  (see  PARAMETERS
              below).   select  then  displays  the PS3 prompt and reads a line from the standard
              input.  If the line consists of a number corresponding  to  one  of  the  displayed
              words, then the value of name is set to that word.  If the line is empty, the words
              and prompt are displayed again.  If EOF is read, the select command  completes  and
              returns  1.   Any other value read causes name to be set to null.  The line read is
              saved in the variable REPLY.  The list is executed after  each  selection  until  a
              break  command  is  executed.   The exit status of select is the exit status of the
              last command executed in list, or zero if no commands were executed.

       case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
              A case command first expands word, and tries to match it against  each  pattern  in
              turn, using the matching rules described under Pattern Matching below.  The word is
              expanded using  tilde  expansion,  parameter  and  variable  expansion,  arithmetic
              expansion,  command  substitution,  process  substitution  and quote removal.  Each
              pattern  examined  is  expanded  using  tilde  expansion,  parameter  and  variable
              expansion,  arithmetic  expansion,  command substitution, process substitution, and
              quote removal.  If the nocasematch shell option is enabled, the match is  performed
              without  regard  to  the case of alphabetic characters.  When a match is found, the
              corresponding list is executed.  If the ;; operator is used, no subsequent  matches
              are  attempted  after  the  first  pattern  match.   Using ;& in place of ;; causes
              execution to continue with the list associated  with  the  next  set  of  patterns.
              Using  ;;&  in  place  of  ;; causes the shell to test the next pattern list in the
              statement, if  any,  and  execute  any  associated  list  on  a  successful  match,
              continuing  the  case  statement  execution as if the pattern list had not matched.
              The exit status is zero if no pattern matches.  Otherwise, it is the exit status of
              the last command executed in list.

       if list; then list; [ elif list; then list; ] ... [ else list; ] fi
              The  if  list  is executed.  If its exit status is zero, the then list is executed.
              Otherwise, each elif list is executed in turn, and if its exit status is zero,  the
              corresponding then list is executed and the command completes.  Otherwise, the else
              list is executed, if present.  The exit status is  the  exit  status  of  the  last
              command executed, or zero if no condition tested true.

       while list-1; do list-2; done
       until list-1; do list-2; done
              The while command continuously executes the list list-2 as long as the last command
              in the list list-1 returns an exit status of zero.  The until command is  identical
              to  the  while command, except that the test is negated: list-2 is executed as long
              as the last command in list-1 returns a non-zero exit status.  The exit  status  of
              the  while  and  until  commands is the exit status of the last command executed in
              list-2, or zero if none was executed.

   Coprocesses
       A coprocess is a shell command preceded by the  coproc  reserved  word.   A  coprocess  is
       executed  asynchronously  in  a subshell, as if the command had been terminated with the &
       control operator, with a two-way pipe established between  the  executing  shell  and  the
       coprocess.

       The syntax for a coprocess is:

              coproc [NAME] command [redirections]

       This creates a coprocess named NAME.  command may be either a simple command or a compound
       command (see above).  NAME is a shell variable name.  If NAME is not supplied, the default
       name is COPROC.

       The recommended form to use for a coprocess is

              coproc NAME { command [redirections]; }

       This  form  is  recommended  because  simple commands result in the coprocess always being
       named COPROC, and it is simpler to use and more complete than the other compound commands.

       If command is a compound command, NAME is optional. The word following  coproc  determines
       whether  that  word  is interpreted as a variable name: it is interpreted as NAME if it is
       not a reserved word that introduces a compound command.  If command is a  simple  command,
       NAME  is  not  allowed;  this is to avoid confusion between NAME and the first word of the
       simple command.

       When the coprocess is executed, the shell creates an array  variable  (see  Arrays  below)
       named  NAME  in  the  context  of  the executing shell.  The standard output of command is
       connected via a pipe to a file descriptor in the executing shell, and that file descriptor
       is  assigned  to NAME[0].  The standard input of command is connected via a pipe to a file
       descriptor in the executing shell, and that file descriptor is assigned to NAME[1].   This
       pipe  is  established  before  any  redirections specified by the command (see REDIRECTION
       below).  The file  descriptors  can  be  utilized  as  arguments  to  shell  commands  and
       redirections  using standard word expansions.  Other than those created to execute command
       and process substitutions, the file descriptors are not available in subshells.

       The process ID of the shell spawned to execute the coprocess is available as the value  of
       the  variable NAME_PID.  The wait builtin command may be used to wait for the coprocess to
       terminate.

       Since the coprocess is created as an  asynchronous  command,  the  coproc  command  always
       returns success.  The return status of a coprocess is the exit status of command.

   Shell Function Definitions
       A shell function is an object that is called like a simple command and executes a compound
       command with a new set of positional parameters.  Shell functions are declared as follows:

       fname () compound-command [redirection]
       function fname [()] compound-command [redirection]
              This defines a function named fname.  The reserved word function is  optional.   If
              the  function reserved word is supplied, the parentheses are optional.  The body of
              the function is  the  compound  command  compound-command  (see  Compound  Commands
              above).  That command is usually a list of commands between { and }, but may be any
              command listed under Compound Commands above.  If the  function  reserved  word  is
              used,   but   the  parentheses  are  not  supplied,  the  braces  are  recommended.
              compound-command is executed whenever fname is specified as the name  of  a  simple
              command.   When  in posix mode, fname must be a valid shell name and may not be the
              name of one of the POSIX special builtins.  In default mode, a function name can be
              any unquoted shell word that does not contain $.  Any redirections (see REDIRECTION
              below) specified when a function is defined are  performed  when  the  function  is
              executed.   The  exit status of a function definition is zero unless a syntax error
              occurs or a readonly function with the same name already  exists.   When  executed,
              the  exit  status  of a function is the exit status of the last command executed in
              the body.  (See FUNCTIONS below.)

COMMENTS

       In a non-interactive shell, or an interactive  shell  in  which  the  interactive_comments
       option  to  the  shopt  builtin  is  enabled  (see  SHELL  BUILTIN COMMANDS below), a word
       beginning with # causes that word and all remaining characters on that line to be ignored.
       An  interactive  shell  without  the  interactive_comments  option  enabled does not allow
       comments.  The interactive_comments option is on by default in interactive shells.

QUOTING

       Quoting is used to remove the special meaning of certain characters or words to the shell.
       Quoting  can  be  used  to  disable  special  treatment for special characters, to prevent
       reserved words from being recognized as such, and to prevent parameter expansion.

       Each of the metacharacters listed above under DEFINITIONS has special meaning to the shell
       and must be quoted if it is to represent itself.

       When  the  command  history  expansion  facilities  are  being used (see HISTORY EXPANSION
       below), the history expansion character, usually !, must  be  quoted  to  prevent  history
       expansion.

       There  are  three  quoting  mechanisms:  the  escape  character, single quotes, and double
       quotes.

       A non-quoted backslash (\) is the escape character.  It preserves the literal value of the
       next  character  that  follows,  with  the  exception  of <newline>.  If a \<newline> pair
       appears, and the backslash is not itself quoted, the  \<newline>  is  treated  as  a  line
       continuation (that is, it is removed from the input stream and effectively ignored).

       Enclosing characters in single quotes preserves the literal value of each character within
       the quotes.  A single quote may not occur between single quotes, even when preceded  by  a
       backslash.

       Enclosing characters in double quotes preserves the literal value of all characters within
       the quotes, with the exception of $, `, \, and, when  history  expansion  is  enabled,  !.
       When  the  shell is in posix mode, the ! has no special meaning within double quotes, even
       when history expansion is enabled.  The characters $ and ` retain  their  special  meaning
       within double quotes.  The backslash retains its special meaning only when followed by one
       of the following characters: $, `, ", \, or <newline>.   A  double  quote  may  be  quoted
       within double quotes by preceding it with a backslash.  If enabled, history expansion will
       be performed unless an !  appearing in double quotes is escaped using  a  backslash.   The
       backslash preceding the !  is not removed.

       The  special parameters * and @ have special meaning when in double quotes (see PARAMETERS
       below).

       Character sequences of the form $'string' are treated  as  a  special  variant  of  single
       quotes.   The  sequence  expands  to  string,  with backslash-escaped characters in string
       replaced as specified by the ANSI C standard.  Backslash escape sequences, if present, are
       decoded as follows:
              \a     alert (bell)
              \b     backspace
              \e
              \E     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \'     single quote
              \"     double quote
              \?     question mark
              \nnn   the  eight-bit  character  whose  value is the octal value nnn (one to three
                     octal digits)
              \xHH   the eight-bit character whose value is the hexadecimal value HH (one or  two
                     hex digits)
              \uHHHH the  Unicode  (ISO/IEC 10646) character whose value is the hexadecimal value
                     HHHH (one to four hex digits)
              \UHHHHHHHH
                     the Unicode (ISO/IEC 10646) character whose value is the  hexadecimal  value
                     HHHHHHHH (one to eight hex digits)
              \cx    a control-x character

       The expanded result is single-quoted, as if the dollar sign had not been present.

       A  double-quoted  string preceded by a dollar sign ($"string") will cause the string to be
       translated according to the current  locale.   The  gettext  infrastructure  performs  the
       lookup  and  translation,  using  the  LC_MESSAGES,  TEXTDOMAINDIR,  and  TEXTDOMAIN shell
       variables.  If the current locale is C or POSIX, if there are no  translations  available,
       or  if the string is not translated, the dollar sign is ignored.  This is a form of double
       quoting, so the string remains double-quoted by default, whether or not it  is  translated
       and  replaced.   If  the  noexpand_translation  option is enabled using the shopt builtin,
       translated strings are single-quoted instead of double-quoted.   See  the  description  of
       shopt below under SHELLBUILTINCOMMANDS.

PARAMETERS

       A  parameter  is  an entity that stores values.  It can be a name, a number, or one of the
       special characters listed below under Special  Parameters.   A  variable  is  a  parameter
       denoted  by  a  name.  A variable has a value and zero or more attributes.  Attributes are
       assigned using the declare builtin command (see declare below in SHELL BUILTIN COMMANDS).

       A parameter is set if it has been assigned a value.  The null string  is  a  valid  value.
       Once a variable is set, it may be unset only by using the unset builtin command (see SHELL
       BUILTIN COMMANDS below).

       A variable may be assigned to by a statement of the form

              name=[value]

       If value is not given, the variable is assigned the null string.  All values undergo tilde
       expansion,  parameter  and variable expansion, command substitution, arithmetic expansion,
       and quote removal (see EXPANSION below).  If the variable has its integer  attribute  set,
       then  value is evaluated as an arithmetic expression even if the $((...)) expansion is not
       used (see Arithmetic Expansion below).  Word splitting  and  pathname  expansion  are  not
       performed.   Assignment  statements  may  also  appear as arguments to the alias, declare,
       typeset, export, readonly, and local builtin commands  (declaration  commands).   When  in
       posix  mode,  these  builtins  may  appear in a command after one or more instances of the
       command builtin and retain these assignment statement properties.

       In the context where an assignment statement is assigning a value to a shell  variable  or
       array  index,  the  += operator can be used to append to or add to the variable's previous
       value.  This includes arguments to builtin commands such as declare that accept assignment
       statements (declaration commands).  When += is applied to a variable for which the integer
       attribute has been set, value is evaluated as an arithmetic expression and  added  to  the
       variable's  current  value,  which  is  also  evaluated.   When  += is applied to an array
       variable using compound assignment (see Arrays below), the variable's value is  not  unset
       (as it is when using =), and new values are appended to the array beginning at one greater
       than the array's maximum index (for indexed arrays) or added as additional key-value pairs
       in  an associative array.  When applied to a string-valued variable, value is expanded and
       appended to the variable's value.

       A variable can be assigned the nameref attribute using the -n option  to  the  declare  or
       local  builtin  commands  (see  the  descriptions  of declare and local below) to create a
       nameref, or a reference to another variable.  This  allows  variables  to  be  manipulated
       indirectly.   Whenever  the nameref variable is referenced, assigned to, unset, or has its
       attributes modified (other than using or  changing  the  nameref  attribute  itself),  the
       operation is actually performed on the variable specified by the nameref variable's value.
       A nameref is commonly used within shell functions to refer to a  variable  whose  name  is
       passed  as  an  argument to the function.  For instance, if a variable name is passed to a
       shell function as its first argument, running
              declare -n ref=$1
       inside the function creates a nameref variable ref whose value is the variable name passed
       as  the first argument.  References and assignments to ref, and changes to its attributes,
       are treated as references, assignments, and attribute modifications to the variable  whose
       name  was  passed as $1.  If the control variable in a for loop has the nameref attribute,
       the list of words can be a  list  of  shell  variables,  and  a  name  reference  will  be
       established  for  each  word  in  the  list,  in  turn,  when the loop is executed.  Array
       variables cannot be given the nameref attribute.  However, nameref variables can reference
       array  variables  and  subscripted  array  variables.   Namerefs can be unset using the -n
       option to the unset builtin.  Otherwise, if unset is executed with the name of  a  nameref
       variable as an argument, the variable referenced by the nameref variable will be unset.

   Positional Parameters
       A positional parameter is a parameter denoted by one or more digits, other than the single
       digit 0.  Positional parameters are  assigned  from  the  shell's  arguments  when  it  is
       invoked,  and  may be reassigned using the set builtin command.  Positional parameters may
       not be assigned to with assignment statements.  The positional parameters are  temporarily
       replaced when a shell function is executed (see FUNCTIONS below).

       When a positional parameter consisting of more than a single digit is expanded, it must be
       enclosed in braces (see EXPANSION below).

   Special Parameters
       The shell treats several parameters specially.  These parameters may only  be  referenced;
       assignment to them is not allowed.
       *      Expands to the positional parameters, starting from one.  When the expansion is not
              within double quotes, each positional parameter expands to  a  separate  word.   In
              contexts  where  it is performed, those words are subject to further word splitting
              and pathname expansion.  When the expansion occurs within double quotes, it expands
              to  a single word with the value of each parameter separated by the first character
              of the IFS special variable.  That is, "$*" is equivalent to "$1c$2c...",  where  c
              is  the  first  character  of  the value of the IFS variable.  If IFS is unset, the
              parameters are separated by spaces.  If IFS is  null,  the  parameters  are  joined
              without intervening separators.
       @      Expands  to  the  positional parameters, starting from one.  In contexts where word
              splitting is performed, this expands each positional parameter to a separate  word;
              if  not  within  double  quotes,  these  words  are  subject to word splitting.  In
              contexts where word splitting is not performed, this expands to a single word  with
              each  positional  parameter separated by a space.  When the expansion occurs within
              double quotes, each parameter expands  to  a  separate  word.   That  is,  "$@"  is
              equivalent  to  "$1" "$2" ...  If the double-quoted expansion occurs within a word,
              the expansion of the first parameter is joined  with  the  beginning  part  of  the
              original word, and the expansion of the last parameter is joined with the last part
              of the original word.  When there are no positional parameters, "$@" and $@  expand
              to nothing (i.e., they are removed).
       #      Expands to the number of positional parameters in decimal.
       ?      Expands to the exit status of the most recently executed foreground pipeline.
       -      Expands  to  the  current  option  flags  as  specified upon invocation, by the set
              builtin command, or those set by the shell itself (such as the -i option).
       $      Expands to the process ID of the shell. In a subshell, it expands to the process ID
              of the current shell, not the subshell.
       !      Expands  to  the  process  ID  of the job most recently placed into the background,
              whether executed as an asynchronous command  or  using  the  bg  builtin  (see  JOB
              CONTROL below).
       0      Expands  to  the  name  of  the  shell  or  shell  script.   This  is  set at shell
              initialization.  If bash is invoked with a file of commands, $0 is set to the  name
              of  that  file.  If bash is started with the -c option, then $0 is set to the first
              argument after the string to be executed, if one is present.  Otherwise, it is  set
              to the filename used to invoke bash, as given by argument zero.

   Shell Variables
       The following variables are set by the shell:

       _      At  shell  startup,  set  to  the pathname used to invoke the shell or shell script
              being executed as passed  in  the  environment  or  argument  list.   Subsequently,
              expands  to  the  last  argument  to  the  previous  simple command executed in the
              foreground, after expansion.  Also set to the full pathname  used  to  invoke  each
              command  executed  and  placed  in  the environment exported to that command.  When
              checking mail, this parameter holds the name  of  the  mail  file  currently  being
              checked.
       BASH   Expands to the full filename used to invoke this instance of bash.
       BASHOPTS
              A  colon-separated list of enabled shell options.  Each word in the list is a valid
              argument for the -s option to the shopt builtin command (see SHELL BUILTIN COMMANDS
              below).   The  options appearing in BASHOPTS are those reported as on by shopt.  If
              this variable is in the environment when bash starts up, each shell option  in  the
              list will be enabled before reading any startup files.  This variable is read-only.
       BASHPID
              Expands  to the process ID of the current bash process.  This differs from $$ under
              certain circumstances, such as subshells  that  do  not  require  bash  to  be  re-
              initialized.  Assignments to BASHPID have no effect.  If BASHPID is unset, it loses
              its special properties, even if it is subsequently reset.
       BASH_ALIASES
              An associative array variable whose members correspond  to  the  internal  list  of
              aliases as maintained by the alias builtin.  Elements added to this array appear in
              the alias list; however, unsetting array elements currently does not cause  aliases
              to  be removed from the alias list.  If BASH_ALIASES is unset, it loses its special
              properties, even if it is subsequently reset.
       BASH_ARGC
              An array variable whose values are the number of parameters in each  frame  of  the
              current  bash  execution  call  stack.   The  number  of  parameters to the current
              subroutine (shell function or script executed with . or source) is at  the  top  of
              the  stack.   When  a  subroutine  is  executed, the number of parameters passed is
              pushed onto BASH_ARGC.  The shell sets BASH_ARGC only when  in  extended  debugging
              mode  (see  the  description  of  the  extdebug option to the shopt builtin below).
              Setting extdebug after the shell has started to execute a  script,  or  referencing
              this variable when extdebug is not set, may result in inconsistent values.
       BASH_ARGV
              An  array  variable  containing all of the parameters in the current bash execution
              call stack.  The final parameter of the last subroutine call is at the top  of  the
              stack; the first parameter of the initial call is at the bottom.  When a subroutine
              is executed, the parameters supplied are pushed onto  BASH_ARGV.   The  shell  sets
              BASH_ARGV only when in extended debugging mode (see the description of the extdebug
              option to the shopt builtin below).  Setting extdebug after the shell  has  started
              to  execute  a  script,  or referencing this variable when extdebug is not set, may
              result in inconsistent values.
       BASH_ARGV0
              When referenced, this variable expands to the name of the  shell  or  shell  script
              (identical to $0; see the description of special parameter 0 above).  Assignment to
              BASH_ARGV0 causes the value assigned to also be assigned to $0.  If  BASH_ARGV0  is
              unset, it loses its special properties, even if it is subsequently reset.
       BASH_CMDS
              An  associative  array variable whose members correspond to the internal hash table
              of commands as maintained by the hash builtin.  Elements added to this array appear
              in  the  hash  table;  however,  unsetting  array elements currently does not cause
              command names to be removed from the hash table.  If BASH_CMDS is unset,  it  loses
              its special properties, even if it is subsequently reset.
       BASH_COMMAND
              The  command  currently being executed or about to be executed, unless the shell is
              executing a command as the result of a trap,  in  which  case  it  is  the  command
              executing  at the time of the trap.  If BASH_COMMAND is unset, it loses its special
              properties, even if it is subsequently reset.
       BASH_EXECUTION_STRING
              The command argument to the -c invocation option.
       BASH_LINENO
              An array variable whose members are the line numbers in  source  files  where  each
              corresponding  member  of  FUNCNAME  was  invoked.   ${BASH_LINENO[$i]} is the line
              number in the source file (${BASH_SOURCE[$i+1]}) where ${FUNCNAME[$i]}  was  called
              (or  ${BASH_LINENO[$i-1]} if referenced within another shell function).  Use LINENO
              to obtain the current line number.
       BASH_LOADABLES_PATH
              A colon-separated list of directories in which  the  shell  looks  for  dynamically
              loadable builtins specified by the enable command.
       BASH_REMATCH
              An  array  variable  whose members are assigned by the =~ binary operator to the [[
              conditional command.  The element with  index  0  is  the  portion  of  the  string
              matching the entire regular expression.  The element with index n is the portion of
              the string matching the nth parenthesized subexpression.
       BASH_SOURCE
              An array variable whose members are the source filenames  where  the  corresponding
              shell  function  names  in  the  FUNCNAME  array  variable  are defined.  The shell
              function ${FUNCNAME[$i]} is defined in the file ${BASH_SOURCE[$i]} and called  from
              ${BASH_SOURCE[$i+1]}.
       BASH_SUBSHELL
              Incremented  by  one  within  each  subshell or subshell environment when the shell
              begins executing in that environment.  The initial value is 0.  If BASH_SUBSHELL is
              unset, it loses its special properties, even if it is subsequently reset.
       BASH_VERSINFO
              A  readonly array variable whose members hold version information for this instance
              of bash.  The values assigned to the array members are as follows:
              BASH_VERSINFO[0]        The major version number (the release).
              BASH_VERSINFO[1]        The minor version number (the version).
              BASH_VERSINFO[2]        The patch level.
              BASH_VERSINFO[3]        The build version.
              BASH_VERSINFO[4]        The release status (e.g., beta1).
              BASH_VERSINFO[5]        The value of MACHTYPE.
       BASH_VERSION
              Expands to a string describing the version of this instance of bash.
       COMP_CWORD
              An index into ${COMP_WORDS} of the word containing  the  current  cursor  position.
              This  variable  is  available  only  in shell functions invoked by the programmable
              completion facilities (see Programmable Completion below).
       COMP_KEY
              The key (or final key of a key sequence) used  to  invoke  the  current  completion
              function.
       COMP_LINE
              The  current  command line.  This variable is available only in shell functions and
              external  commands  invoked  by  the  programmable   completion   facilities   (see
              Programmable Completion below).
       COMP_POINT
              The  index  of the current cursor position relative to the beginning of the current
              command.  If the current cursor position is at the end of the current command,  the
              value  of this variable is equal to ${#COMP_LINE}.  This variable is available only
              in shell functions and external commands invoked  by  the  programmable  completion
              facilities (see Programmable Completion below).
       COMP_TYPE
              Set  to  an  integer  value  corresponding to the type of completion attempted that
              caused a completion function to be called:  TAB,  for  normal  completion,  ?,  for
              listing  completions  after successive tabs, !, for listing alternatives on partial
              word completion, @, to list completions if the word is not unmodified,  or  %,  for
              menu  completion.   This variable is available only in shell functions and external
              commands invoked  by  the  programmable  completion  facilities  (see  Programmable
              Completion below).
       COMP_WORDBREAKS
              The  set  of  characters  that  the readline library treats as word separators when
              performing word completion.  If COMP_WORDBREAKS is  unset,  it  loses  its  special
              properties, even if it is subsequently reset.
       COMP_WORDS
              An  array  variable  (see  Arrays  below) consisting of the individual words in the
              current command line.  The line is split into words as  readline  would  split  it,
              using COMP_WORDBREAKS as described above.  This variable is available only in shell
              functions invoked by  the  programmable  completion  facilities  (see  Programmable
              Completion below).
       COPROC An  array  variable  (see  Arrays  below)  created to hold the file descriptors for
              output from and input to an unnamed coprocess (see Coprocesses above).
       DIRSTACK
              An array variable (see  Arrays  below)  containing  the  current  contents  of  the
              directory  stack.   Directories appear in the stack in the order they are displayed
              by the dirs builtin.  Assigning to members of this array variable may  be  used  to
              modify  directories  already  in the stack, but the pushd and popd builtins must be
              used to add and remove directories.  Assignment to this variable  will  not  change
              the current directory.  If DIRSTACK is unset, it loses its special properties, even
              if it is subsequently reset.
       EPOCHREALTIME
              Each time this parameter is referenced, it expands to the number of  seconds  since
              the  Unix  Epoch  (see  time(3))  as  a  floating  point  value  with  micro-second
              granularity.  Assignments to EPOCHREALTIME are ignored.  If EPOCHREALTIME is unset,
              it loses its special properties, even if it is subsequently reset.
       EPOCHSECONDS
              Each  time  this parameter is referenced, it expands to the number of seconds since
              the Unix Epoch  (see  time(3)).   Assignments  to  EPOCHSECONDS  are  ignored.   If
              EPOCHSECONDS  is unset, it loses its special properties, even if it is subsequently
              reset.
       EUID   Expands to the effective user ID of the current user, initialized at shell startup.
              This variable is readonly.
       FUNCNAME
              An  array  variable  containing  the  names of all shell functions currently in the
              execution call stack.  The element with index 0  is  the  name  of  any  currently-
              executing shell function.  The bottom-most element (the one with the highest index)
              is "main".   This  variable  exists  only  when  a  shell  function  is  executing.
              Assignments to FUNCNAME have no effect.  If FUNCNAME is unset, it loses its special
              properties, even if it is subsequently reset.

              This variable can be used  with  BASH_LINENO  and  BASH_SOURCE.   Each  element  of
              FUNCNAME  has corresponding elements in BASH_LINENO and BASH_SOURCE to describe the
              call  stack.   For   instance,   ${FUNCNAME[$i]}   was   called   from   the   file
              ${BASH_SOURCE[$i+1]}   at  line  number  ${BASH_LINENO[$i]}.   The  caller  builtin
              displays the current call stack using this information.
       GROUPS An array variable containing the list of groups of which  the  current  user  is  a
              member.   Assignments  to  GROUPS have no effect.  If GROUPS is unset, it loses its
              special properties, even if it is subsequently reset.
       HISTCMD
              The history number,  or  index  in  the  history  list,  of  the  current  command.
              Assignments  to  HISTCMD  are  ignored.   If HISTCMD is unset, it loses its special
              properties, even if it is subsequently reset.
       HOSTNAME
              Automatically set to the name of the current host.
       HOSTTYPE
              Automatically set to a string that uniquely describes the type of machine on  which
              bash is executing.  The default is system-dependent.
       LINENO Each  time  this  parameter  is  referenced, the shell substitutes a decimal number
              representing the current sequential line number (starting with 1) within  a  script
              or  function.   When  not  in  a  script  or function, the value substituted is not
              guaranteed to be meaningful.  If LINENO is unset, it loses its special  properties,
              even if it is subsequently reset.
       MACHTYPE
              Automatically set to a string that fully describes the system type on which bash is
              executing, in the standard GNU cpu-company-system format.  The default  is  system-
              dependent.
       MAPFILE
              An  array  variable (see Arrays below) created to hold the text read by the mapfile
              builtin when no variable name is supplied.
       OLDPWD The previous working directory as set by the cd command.
       OPTARG The value of the last option argument processed by the getopts builtin command (see
              SHELL BUILTIN COMMANDS below).
       OPTIND The  index of the next argument to be processed by the getopts builtin command (see
              SHELL BUILTIN COMMANDS below).
       OSTYPE Automatically set to a string that describes the operating system on which bash  is
              executing.  The default is system-dependent.
       PIPESTATUS
              An  array  variable (see Arrays below) containing a list of exit status values from
              the processes in the most-recently-executed foreground pipeline (which may  contain
              only a single command).
       PPID   The process ID of the shell's parent.  This variable is readonly.
       PWD    The current working directory as set by the cd command.
       RANDOM Each  time  this  parameter is referenced, it expands to a random integer between 0
              and 32767.  Assigning a value to RANDOM initializes (seeds) the sequence of  random
              numbers.   If  RANDOM  is  unset,  it  loses  its special properties, even if it is
              subsequently reset.
       READLINE_ARGUMENT
              Any numeric argument given to a readline command that was defined using  "bind  -x"
              (see SHELL BUILTIN COMMANDS below) when it was invoked.
       READLINE_LINE
              The contents of the readline line buffer, for use with "bind -x" (see SHELL BUILTIN
              COMMANDS below).
       READLINE_MARK
              The position of the mark (saved insertion point) in the readline line  buffer,  for
              use  with "bind -x" (see SHELL BUILTIN COMMANDS below).  The characters between the
              insertion point and the mark are often called the region.
       READLINE_POINT
              The position of the insertion point in the readline line buffer, for use with "bind
              -x" (see SHELL BUILTIN COMMANDS below).
       REPLY  Set  to  the  line  of input read by the read builtin command when no arguments are
              supplied.
       SECONDS
              Each time this parameter is referenced, it expands to the number of  seconds  since
              shell  invocation.   If  a  value  is  assigned to SECONDS, the value returned upon
              subsequent references is the number of seconds since the assignment plus the  value
              assigned.   The  number  of  seconds  at  shell invocation and the current time are
              always determined by querying the system clock.  If SECONDS is unset, it loses  its
              special properties, even if it is subsequently reset.
       SHELLOPTS
              A  colon-separated list of enabled shell options.  Each word in the list is a valid
              argument for the -o option to the set builtin command (see SHELL  BUILTIN  COMMANDS
              below).  The options appearing in SHELLOPTS are those reported as on by set -o.  If
              this variable is in the environment when bash starts up, each shell option  in  the
              list will be enabled before reading any startup files.  This variable is read-only.
       SHLVL  Incremented by one each time an instance of bash is started.
       SRANDOM
              This  variable expands to a 32-bit pseudo-random number each time it is referenced.
              The random number generator is not linear on systems that support  /dev/urandom  or
              arc4random,  so  each  returned number has no relationship to the numbers preceding
              it.  The random number generator cannot be seeded, so assignments to this  variable
              have  no  effect.  If SRANDOM is unset, it loses its special properties, even if it
              is subsequently reset.
       UID    Expands to the user ID of the current user, initialized  at  shell  startup.   This
              variable is readonly.

       The  following  variables  are  used  by the shell.  In some cases, bash assigns a default
       value to a variable; these cases are noted below.

       BASH_COMPAT
              The value is used to set the shell's compatibility level.  See SHELL  COMPATIBILITY
              MODE below for a description of the various compatibility levels and their effects.
              The  value  may  be  a  decimal  number  (e.g.,  4.2)  or  an  integer  (e.g.,  42)
              corresponding  to  the desired compatibility level.  If BASH_COMPAT is unset or set
              to the empty string, the compatibility level is set to the default for the  current
              version.   If  BASH_COMPAT  is  set  to  a  value  that  is  not  one  of the valid
              compatibility levels, the shell prints an error message and sets the  compatibility
              level  to  the default for the current version.  The valid values correspond to the
              compatibility levels described below under SHELL COMPATIBILITY MODE.  For  example,
              4.2  and  42  are valid values that correspond to the compat42 shopt option and set
              the compatibility level to 42.  The current version is also a valid value.
       BASH_ENV
              If this parameter is set when bash is  executing  a  shell  script,  its  value  is
              interpreted  as  a  filename  containing  commands  to  initialize the shell, as in
              ~/.bashrc.  The value of BASH_ENV is  subjected  to  parameter  expansion,  command
              substitution,  and  arithmetic  expansion  before  being interpreted as a filename.
              PATH is not used to search for the resultant filename.
       BASH_XTRACEFD
              If set to an integer corresponding to a valid file descriptor, bash will write  the
              trace  output  generated  when set -x is enabled to that file descriptor.  The file
              descriptor is  closed  when  BASH_XTRACEFD  is  unset  or  assigned  a  new  value.
              Unsetting BASH_XTRACEFD or assigning it the empty string causes the trace output to
              be sent to the standard error.  Note that setting BASH_XTRACEFD to 2 (the  standard
              error  file  descriptor)  and  then  unsetting it will result in the standard error
              being closed.
       CDPATH The search path for the cd command.  This is a colon-separated list of  directories
              in  which  the shell looks for destination directories specified by the cd command.
              A sample value is ".:~:/usr".
       CHILD_MAX
              Set the number of exited child status values for the shell to remember.  Bash  will
              not allow this value to be decreased below a POSIX-mandated minimum, and there is a
              maximum value (currently 8192) that this may not  exceed.   The  minimum  value  is
              system-dependent.
       COLUMNS
              Used  by  the select compound command to determine the terminal width when printing
              selection lists.  Automatically set if the checkwinsize option is enabled or in  an
              interactive shell upon receipt of a SIGWINCH.
       COMPREPLY
              An  array  variable  from  which bash reads the possible completions generated by a
              shell function invoked by the programmable completion  facility  (see  Programmable
              Completion below).  Each array element contains one possible completion.
       EMACS  If  bash  finds  this  variable in the environment when the shell starts with value
              "t", it assumes that the shell is running in an Emacs  shell  buffer  and  disables
              line editing.
       ENV    Expanded  and  executed  similarly  to  BASH_ENV  (see  INVOCATION  above)  when an
              interactive shell is invoked in posix mode.
       EXECIGNORE
              A colon-separated list of shell patterns (see Pattern Matching) defining  the  list
              of  filenames  to  be  ignored  by  command  search  using  PATH.  Files whose full
              pathnames match one of these patterns are not considered executable files  for  the
              purposes of completion and command execution via PATH lookup.  This does not affect
              the behavior of the [, test, and [[ commands.  Full pathnames in the  command  hash
              table  are  not  subject to EXECIGNORE.  Use this variable to ignore shared library
              files that have the executable bit set, but are not executable files.  The  pattern
              matching honors the setting of the extglob shell option.
       FCEDIT The default editor for the fc builtin command.
       FIGNORE
              A  colon-separated  list  of suffixes to ignore when performing filename completion
              (see READLINE below).  A filename whose  suffix  matches  one  of  the  entries  in
              FIGNORE  is  excluded from the list of matched filenames.  A sample value is ".o:~"
              (Quoting is needed when assigning a value to this variable, which contains tildes).
       FUNCNEST
              If set to a numeric value greater than 0, defines a maximum function nesting level.
              Function  invocations that exceed this nesting level will cause the current command
              to abort.
       GLOBIGNORE
              A colon-separated list of patterns defining the set of file names to be ignored  by
              pathname  expansion.   If  a file name matched by a pathname expansion pattern also
              matches one of the patterns in GLOBIGNORE, it is removed from the list of matches.
       HISTCONTROL
              A colon-separated list of values controlling how commands are saved on the  history
              list.   If  the list of values includes ignorespace, lines which begin with a space
              character are not saved in the history list.  A value of  ignoredups  causes  lines
              matching  the  previous  history  entry  to not be saved.  A value of ignoreboth is
              shorthand for ignorespace and ignoredups.  A value of erasedups causes all previous
              lines  matching  the  current  line to be removed from the history list before that
              line is saved.  Any value not in the above list  is  ignored.   If  HISTCONTROL  is
              unset,  or  does  not include a valid value, all lines read by the shell parser are
              saved on the history list, subject to the value  of  HISTIGNORE.   The  second  and
              subsequent  lines of a multi-line compound command are not tested, and are added to
              the history regardless of the value of HISTCONTROL.
       HISTFILE
              The name of the file in which command history is saved (see  HISTORY  below).   The
              default  value is ~/.bash_history.  If unset, the command history is not saved when
              a shell exits.
       HISTFILESIZE
              The maximum number of lines contained in the history file.  When this  variable  is
              assigned  a  value, the history file is truncated, if necessary, to contain no more
              than that number of lines by removing the oldest entries.  The history file is also
              truncated to this size after writing it when a shell exits.  If the value is 0, the
              history file is truncated to zero size.  Non-numeric values and numeric values less
              than  zero  inhibit  truncation.   The shell sets the default value to the value of
              HISTSIZE after reading any startup files.
       HISTIGNORE
              A colon-separated list of patterns used to decide which  command  lines  should  be
              saved  on  the history list.  Each pattern is anchored at the beginning of the line
              and must match the complete line (no implicit `*' is appended).   Each  pattern  is
              tested  against the line after the checks specified by HISTCONTROL are applied.  In
              addition to the normal shell pattern matching characters, `&' matches the  previous
              history  line.   `&'  may  be  escaped  using a backslash; the backslash is removed
              before attempting a match.   The  second  and  subsequent  lines  of  a  multi-line
              compound  command  are  not  tested, and are added to the history regardless of the
              value of HISTIGNORE.  The pattern matching honors the setting of the extglob  shell
              option.
       HISTSIZE
              The  number of commands to remember in the command history (see HISTORY below).  If
              the value is 0, commands are not saved in the history list.   Numeric  values  less
              than  zero  result  in  every  command being saved on the history list (there is no
              limit).  The shell sets the default value to 500 after reading any startup files.
       HISTTIMEFORMAT
              If this variable is set and not null, its value is used  as  a  format  string  for
              strftime(3) to print the time stamp associated with each history entry displayed by
              the history builtin.  If this variable is set,  time  stamps  are  written  to  the
              history file so they may be preserved across shell sessions.  This uses the history
              comment character to distinguish timestamps from other history lines.
       HOME   The home directory of the current user; the default argument  for  the  cd  builtin
              command.  The value of this variable is also used when performing tilde expansion.
       HOSTFILE
              Contains  the  name  of a file in the same format as /etc/hosts that should be read
              when the shell needs to  complete  a  hostname.   The  list  of  possible  hostname
              completions  may  be  changed  while  the  shell is running; the next time hostname
              completion is attempted after the value is changed, bash adds the contents  of  the
              new  file  to the existing list.  If HOSTFILE is set, but has no value, or does not
              name a readable file, bash attempts to  read  /etc/hosts  to  obtain  the  list  of
              possible  hostname  completions.   When  HOSTFILE  is  unset,  the hostname list is
              cleared.
       IFS    The Internal Field Separator that is used for word splitting after expansion and to
              split  lines  into  words  with  the  read  builtin  command.  The default value is
              ``<space><tab><newline>''.
       IGNOREEOF
              Controls the action of an interactive shell on receipt of an EOF character  as  the
              sole  input.   If  set, the value is the number of consecutive EOF characters which
              must be typed as the first characters on an input line before bash exits.   If  the
              variable  exists  but  does  not have a numeric value, or has no value, the default
              value is 10.  If it does not exist, EOF signifies the end of input to the shell.
       INPUTRC
              The filename for the readline startup file, overriding the  default  of  ~/.inputrc
              (see READLINE below).
       INSIDE_EMACS
              If  this  variable  appears  in the environment when the shell starts, bash assumes
              that it is running inside an Emacs shell  buffer  and  may  disable  line  editing,
              depending on the value of TERM.
       LANG   Used  to  determine  the locale category for any category not specifically selected
              with a variable starting with LC_.
       LC_ALL This variable overrides the value of LANG and any other LC_ variable  specifying  a
              locale category.
       LC_COLLATE
              This  variable  determines  the  collation  order  used when sorting the results of
              pathname expansion, and determines the behavior of range  expressions,  equivalence
              classes, and collating sequences within pathname expansion and pattern matching.
       LC_CTYPE
              This  variable  determines  the  interpretation  of  characters and the behavior of
              character classes within pathname expansion and pattern matching.
       LC_MESSAGES
              This variable  determines  the  locale  used  to  translate  double-quoted  strings
              preceded by a $.
       LC_NUMERIC
              This variable determines the locale category used for number formatting.
       LC_TIME
              This variable determines the locale category used for data and time formatting.
       LINES  Used  by  the  select  compound command to determine the column length for printing
              selection lists.  Automatically set if the checkwinsize option is enabled or in  an
              interactive shell upon receipt of a SIGWINCH.
       MAIL   If  this  parameter is set to a file or directory name and the MAILPATH variable is
              not set, bash informs the user of the arrival of mail  in  the  specified  file  or
              Maildir-format directory.
       MAILCHECK
              Specifies  how often (in seconds) bash checks for mail.  The default is 60 seconds.
              When it is time to check for mail, the shell does so before displaying the  primary
              prompt.   If this variable is unset, or set to a value that is not a number greater
              than or equal to zero, the shell disables mail checking.
       MAILPATH
              A colon-separated list of filenames to be checked for  mail.   The  message  to  be
              printed  when  mail arrives in a particular file may be specified by separating the
              filename from the message with a `?'.  When used in the text  of  the  message,  $_
              expands to the name of the current mailfile.  Example:
              MAILPATH='/var/mail/bfox?"You have mail":~/shell-mail?"$_ has mail!"'
              Bash  can  be  configured  to supply a default value for this variable (there is no
              value by default), but the location of the user mail files that it uses  is  system
              dependent (e.g., /var/mail/$USER).
       OPTERR If  set  to  the  value  1,  bash  displays error messages generated by the getopts
              builtin command (see SHELL BUILTIN COMMANDS below).  OPTERR  is  initialized  to  1
              each time the shell is invoked or a shell script is executed.
       PATH   The search path for commands.  It is a colon-separated list of directories in which
              the shell looks for commands (see COMMAND EXECUTION below).  A  zero-length  (null)
              directory  name  in  the  value  of  PATH  indicates the current directory.  A null
              directory name may appear as two adjacent colons, or  as  an  initial  or  trailing
              colon.   The  default path is system-dependent, and is set by the administrator who
              installs bash.  A common value is ``/usr/local/bin:/usr/local/sbin:/usr/bin:
              /usr/sbin:/bin:/sbin''.
       POSIXLY_CORRECT
              If  this  variable  is  in the environment when bash starts, the shell enters posix
              mode before reading the startup files, as if the --posix invocation option had been
              supplied.   If it is set while the shell is running, bash enables posix mode, as if
              the command set -o posix had been executed.  When the shell enters posix  mode,  it
              sets this variable if it was not already set.
       PROMPT_COMMAND
              If this variable is set, and is an array, the value of each set element is executed
              as a command prior to issuing each primary prompt.  If this is set but not an array
              variable, its value is used as a command to execute instead.
       PROMPT_DIRTRIM
              If  set  to a number greater than zero, the value is used as the number of trailing
              directory components to retain when expanding the \w and \W prompt  string  escapes
              (see PROMPTING below).  Characters removed are replaced with an ellipsis.
       PS0    The  value  of  this  parameter  is expanded (see PROMPTING below) and displayed by
              interactive shells after reading a command and before the command is executed.
       PS1    The value of this parameter is expanded (see  PROMPTING  below)  and  used  as  the
              primary prompt string.  The default value is ``\s-\v\$ ''.
       PS2    The  value  of  this  parameter  is  expanded as with PS1 and used as the secondary
              prompt string.  The default is ``> ''.
       PS3    The value of this parameter is used as the prompt for the select command (see SHELL
              GRAMMAR above).
       PS4    The value of this parameter is expanded as with PS1 and the value is printed before
              each command bash displays during an execution trace.  The first character  of  the
              expanded  value  of  PS4  is  replicated  multiple times, as necessary, to indicate
              multiple levels of indirection.  The default is ``+ ''.
       SHELL  This variable expands to the full pathname to the shell.  If it is not set when the
              shell  starts,  bash  assigns  to  it the full pathname of the current user's login
              shell.
       TIMEFORMAT
              The value of this parameter is used as a format string specifying  how  the  timing
              information for pipelines prefixed with the time reserved word should be displayed.
              The % character introduces an escape sequence that is expanded to a time  value  or
              other  information.   The  escape  sequences and their meanings are as follows; the
              braces denote optional portions.
              %%        A literal %.
              %[p][l]R  The elapsed time in seconds.
              %[p][l]U  The number of CPU seconds spent in user mode.
              %[p][l]S  The number of CPU seconds spent in system mode.
              %P        The CPU percentage, computed as (%U + %S) / %R.

              The optional p is a digit specifying the precision, the number of fractional digits
              after  a  decimal  point.   A  value of 0 causes no decimal point or fraction to be
              output.  At most three places after the decimal point may be specified; values of p
              greater than 3 are changed to 3.  If p is not specified, the value 3 is used.

              The optional l specifies a longer format, including minutes, of the form MMmSS.FFs.
              The value of p determines whether or not the fraction is included.

              If  this  variable  is  not   set,   bash   acts   as   if   it   had   the   value
              $'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'.    If   the   value   is  null,  no  timing
              information is displayed.  A trailing newline is added when the  format  string  is
              displayed.
       TMOUT  If  set  to  a value greater than zero, TMOUT is treated as the default timeout for
              the read builtin.  The select command terminates if input  does  not  arrive  after
              TMOUT  seconds  when input is coming from a terminal.  In an interactive shell, the
              value is interpreted as the number of seconds to wait for a  line  of  input  after
              issuing  the  primary  prompt.   Bash  terminates  after waiting for that number of
              seconds if a complete line of input does not arrive.
       TMPDIR If set, bash uses its value as the name  of  a  directory  in  which  bash  creates
              temporary files for the shell's use.
       auto_resume
              This  variable  controls how the shell interacts with the user and job control.  If
              this variable is set, single word simple commands without redirections are  treated
              as  candidates  for  resumption  of an existing stopped job.  There is no ambiguity
              allowed; if there is more than one job beginning with the  string  typed,  the  job
              most recently accessed is selected.  The name of a stopped job, in this context, is
              the command line used to start it.  If set to the value exact, the string  supplied
              must  match  the  name  of  a  stopped job exactly; if set to substring, the string
              supplied needs to match a substring of the name of a stopped  job.   The  substring
              value  provides  functionality analogous to the %?  job identifier (see JOB CONTROL
              below).  If set to any other value, the supplied string  must  be  a  prefix  of  a
              stopped  job's  name;  this  provides  functionality  analogous  to the %string job
              identifier.
       histchars
              The two or three characters which control history expansion and  tokenization  (see
              HISTORY  EXPANSION below).  The first character is the history expansion character,
              the character which signals the start of a history expansion,  normally  `!'.   The
              second  character  is  the quick substitution character, which is used as shorthand
              for re-running the previous command entered, substituting one string for another in
              the  command.   The  default is `^'.  The optional third character is the character
              which indicates that the remainder of the line is a comment when found as the first
              character  of  a  word, normally `#'.  The history comment character causes history
              substitution to be skipped for the remaining  words  on  the  line.   It  does  not
              necessarily cause the shell parser to treat the rest of the line as a comment.

   Arrays
       Bash  provides  one-dimensional indexed and associative array variables.  Any variable may
       be used as an indexed array; the declare builtin will explicitly declare an array.   There
       is  no  maximum limit on the size of an array, nor any requirement that members be indexed
       or assigned  contiguously.   Indexed  arrays  are  referenced  using  integers  (including
       arithmetic  expressions)  and  are  zero-based;  associative  arrays  are referenced using
       arbitrary strings.  Unless otherwise noted, indexed array  indices  must  be  non-negative
       integers.

       An  indexed array is created automatically if any variable is assigned to using the syntax
       name[subscript]=value.  The subscript is treated as an  arithmetic  expression  that  must
       evaluate  to  a  number.  To explicitly declare an indexed array, use declare -a name (see
       SHELL BUILTIN COMMANDS below).  declare -a name[subscript] is also accepted; the subscript
       is ignored.

       Associative arrays are created using declare -A name.

       Attributes may be specified for an array variable using the declare and readonly builtins.
       Each attribute applies to all members of an array.

       Arrays are assigned to using compound assignments of the form  name=(value1  ...  valuen),
       where  each value may be of the form [subscript]=string.  Indexed array assignments do not
       require anything but string.  Each value in the list  is  expanded  using  all  the  shell
       expansions  described  below  under  EXPANSION.   When assigning to indexed arrays, if the
       optional brackets and subscript are supplied, that index is  assigned  to;  otherwise  the
       index  of  the  element  assigned is the last index assigned to by the statement plus one.
       Indexing starts at zero.

       When assigning to an associative array, the words in a compound assignment may  be  either
       assignment  statements,  for  which  the subscript is required, or a list of words that is
       interpreted as a sequence of alternating keys and values: name=( key1 value1  key2  value2
       ...).   These  are  treated  identically  to name=( [key1]=value1 [key2]=value2 ...).  The
       first word in the list determines how the remaining words are interpreted; all assignments
       in  a  list  must  be  of  the same type.  When using key/value pairs, the keys may not be
       missing or empty; a final missing value is treated like the empty string.

       This syntax is also accepted by the declare builtin.  Individual  array  elements  may  be
       assigned to using the name[subscript]=value syntax introduced above.  When assigning to an
       indexed array, if name is subscripted by a negative number, that number is interpreted  as
       relative  to  one  greater  than the maximum index of name, so negative indices count back
       from the end of the array, and an index of -1 references the last element.

       The += operator will append to  an  array  variable  when  assigning  using  the  compound
       assignment syntax; see PARAMETERS above.

       Any  element  of  an  array  may  be  referenced using ${name[subscript]}.  The braces are
       required to avoid conflicts with pathname expansion.  If subscript is @  or  *,  the  word
       expands to all members of name.  These subscripts differ only when the word appears within
       double quotes.  If the word is double-quoted, ${name[*]} expands to a single word with the
       value  of  each array member separated by the first character of the IFS special variable,
       and ${name[@]} expands each element of name to a separate word.  When there are  no  array
       members,  ${name[@]}  expands  to nothing.  If the double-quoted expansion occurs within a
       word, the expansion of the first parameter is  joined  with  the  beginning  part  of  the
       original word, and the expansion of the last parameter is joined with the last part of the
       original word.  This is analogous to the expansion of the special parameters * and @  (see
       Special    Parameters    above).    ${#name[subscript]}   expands   to   the   length   of
       ${name[subscript]}.  If subscript is * or @, the expansion is the number  of  elements  in
       the array.  If the subscript used to reference an element of an indexed array evaluates to
       a number less than zero, it is interpreted as relative to one  greater  than  the  maximum
       index of the array, so negative indices count back from the end of the array, and an index
       of -1 references the last element.

       Referencing an array variable without a subscript is equivalent to referencing  the  array
       with  a subscript of 0.  Any reference to a variable using a valid subscript is legal, and
       bash will create an array if necessary.

       An array variable is considered set if a subscript has been assigned a  value.   The  null
       string is a valid value.

       It  is  possible  to  obtain  the  keys  (indices)  of  an  array  as  well as the values.
       ${!name[@]} and ${!name[*]} expand to the indices assigned in array  variable  name.   The
       treatment  when  in  double quotes is similar to the expansion of the special parameters @
       and * within double quotes.

       The unset builtin is used to destroy arrays.  unset  name[subscript]  destroys  the  array
       element  at index subscript, for both indexed and associative arrays.  Negative subscripts
       to indexed arrays are interpreted as described above.  Unsetting the last  element  of  an
       array  variable  does not unset the variable.  unset name, where name is an array, removes
       the entire array.  unset name[subscript], where subscript is * or @,  behaves  differently
       depending  on  whether name is an indexed or associative array.  If name is an associative
       array, this unsets the element with subscript * or @.  If name is an indexed array,  unset
       removes all of the elements but does not remove the array itself.

       When  using  a  variable  name  with a subscript as an argument to a command, such as with
       unset, without using the word expansion syntax described above, the argument is subject to
       pathname expansion.  If pathname expansion is not desired, the argument should be quoted.

       The  declare,  local,  and readonly builtins each accept a -a option to specify an indexed
       array and a -A option to specify an associative array.  If both options are  supplied,  -A
       takes  precedence.   The  read  builtin accepts a -a option to assign a list of words read
       from the standard input to an array.  The set and declare builtins display array values in
       a way that allows them to be reused as assignments.

EXPANSION

       Expansion  is performed on the command line after it has been split into words.  There are
       seven kinds of expansion  performed:  brace  expansion,  tilde  expansion,  parameter  and
       variable  expansion,  command  substitution,  arithmetic  expansion,  word  splitting, and
       pathname expansion.

       The order of expansions is: brace  expansion;  tilde  expansion,  parameter  and  variable
       expansion,  arithmetic  expansion,  and  command  substitution  (done  in  a left-to-right
       fashion); word splitting; and pathname expansion.

       On systems that can support it,  there  is  an  additional  expansion  available:  process
       substitution.   This  is  performed  at  the  same time as tilde, parameter, variable, and
       arithmetic expansion and command substitution.

       After these expansions are performed, quote characters present in the  original  word  are
       removed unless they have been quoted themselves (quote removal).

       Only  brace  expansion,  word splitting, and pathname expansion can increase the number of
       words of the expansion; other expansions expand a single word to a single word.  The  only
       exceptions to this are the expansions of "$@" and "${name[@]}", and, in most cases, $* and
       ${name[*]} as explained above (see PARAMETERS).

   Brace Expansion
       Brace expansion is a  mechanism  by  which  arbitrary  strings  may  be  generated.   This
       mechanism  is  similar  to pathname expansion, but the filenames generated need not exist.
       Patterns to be brace expanded take the form of an optional preamble, followed by either  a
       series  of  comma-separated  strings  or  a  sequence expression between a pair of braces,
       followed by an optional postscript.  The preamble is prefixed  to  each  string  contained
       within the braces, and the postscript is then appended to each resulting string, expanding
       left to right.

       Brace expansions may be nested.  The results of each expanded string are not sorted;  left
       to right order is preserved.  For example, a{d,c,b}e expands into `ade ace abe'.

       A  sequence expression takes the form {x..y[..incr]}, where x and y are either integers or
       single letters, and incr, an  optional  increment,  is  an  integer.   When  integers  are
       supplied,  the  expression  expands  to  each number between x and y, inclusive.  Supplied
       integers may be prefixed with 0 to force each term to have the same width.  When either  x
       or  y  begins  with a zero, the shell attempts to force all generated terms to contain the
       same number of digits, zero-padding where  necessary.   When  letters  are  supplied,  the
       expression  expands  to each character lexicographically between x and y, inclusive, using
       the default C locale.  Note that both x and y  must  be  of  the  same  type  (integer  or
       letter).   When the increment is supplied, it is used as the difference between each term.
       The default increment is 1 or -1 as appropriate.

       Brace expansion is performed before any other expansions, and any  characters  special  to
       other  expansions  are  preserved  in  the result.  It is strictly textual.  Bash does not
       apply any syntactic interpretation to the context of the expansion or the text between the
       braces.

       A  correctly-formed  brace expansion must contain unquoted opening and closing braces, and
       at least one unquoted comma or a valid sequence expression.  Any incorrectly formed  brace
       expansion is left unchanged.  A { or , may be quoted with a backslash to prevent its being
       considered part of a brace expression.  To avoid conflicts with parameter  expansion,  the
       string  ${  is  not  considered eligible for brace expansion, and inhibits brace expansion
       until the closing }.

       This construct is typically used as shorthand when the common prefix of the strings to  be
       generated is longer than in the above example:

              mkdir /usr/local/src/bash/{old,new,dist,bugs}
       or
              chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}

       Brace  expansion  introduces  a slight incompatibility with historical versions of sh.  sh
       does not treat opening or closing braces specially when they appear as part of a word, and
       preserves  them  in  the output.  Bash removes braces from words as a consequence of brace
       expansion.  For example, a word entered to sh as  file{1,2}  appears  identically  in  the
       output.   The  same  word  is  output  as  file1 file2 after expansion by bash.  If strict
       compatibility with sh is desired, start bash with the +B option or disable brace expansion
       with the +B option to the set command (see SHELL BUILTIN COMMANDS below).

   Tilde Expansion
       If  a  word begins with an unquoted tilde character (`~'), all of the characters preceding
       the first unquoted slash (or all characters, if there is no unquoted slash) are considered
       a  tilde-prefix.  If none of the characters in the tilde-prefix are quoted, the characters
       in the tilde-prefix following the tilde are treated as a possible  login  name.   If  this
       login name is the null string, the tilde is replaced with the value of the shell parameter
       HOME.  If HOME is unset, the home directory of the user executing the shell is substituted
       instead.   Otherwise, the tilde-prefix is replaced with the home directory associated with
       the specified login name.

       If the tilde-prefix is a `~+', the value of the shell variable  PWD  replaces  the  tilde-
       prefix.   If  the tilde-prefix is a `~-', the value of the shell variable OLDPWD, if it is
       set, is substituted.  If the characters following the tilde in the tilde-prefix consist of
       a  number  N, optionally prefixed by a `+' or a `-', the tilde-prefix is replaced with the
       corresponding element from the directory stack, as it  would  be  displayed  by  the  dirs
       builtin  invoked  with  the  tilde-prefix as an argument.  If the characters following the
       tilde in the tilde-prefix consist of a number  without  a  leading  `+'  or  `-',  `+'  is
       assumed.

       If the login name is invalid, or the tilde expansion fails, the word is unchanged.

       Each  variable assignment is checked for unquoted tilde-prefixes immediately following a :
       or the first =.  In these cases, tilde expansion is also performed.  Consequently, one may
       use  filenames  with  tildes  in  assignments to PATH, MAILPATH, and CDPATH, and the shell
       assigns the expanded value.

       Bash also performs  tilde  expansion  on  words  satisfying  the  conditions  of  variable
       assignments  (as described above under PARAMETERS) when they appear as arguments to simple
       commands.  Bash does not do this, except for the declaration commands listed  above,  when
       in posix mode.

   Parameter Expansion
       The  `$'  character  introduces  parameter  expansion, command substitution, or arithmetic
       expansion.  The parameter name or symbol to be expanded may be enclosed in  braces,  which
       are  optional but serve to protect the variable to be expanded from characters immediately
       following it which could be interpreted as part of the name.

       When braces are used, the matching ending  brace  is  the  first  `}'  not  escaped  by  a
       backslash  or  within  a  quoted  string, and not within an embedded arithmetic expansion,
       command substitution, or parameter expansion.

       ${parameter}
              The value of parameter is substituted.  The braces are required when parameter is a
              positional  parameter  with more than one digit, or when parameter is followed by a
              character which is not to be interpreted as part of its name.  The parameter  is  a
              shell parameter as described above PARAMETERS) or an array reference (Arrays).

       If  the  first  character of parameter is an exclamation point (!), and parameter is not a
       nameref, it introduces a level of indirection.  Bash uses the value  formed  by  expanding
       the  rest  of parameter as the new parameter; this is then expanded and that value is used
       in the rest of the expansion, rather than the expansion of the original  parameter.   This
       is  known  as  indirect  expansion.   The  value  is subject to tilde expansion, parameter
       expansion, command substitution, and arithmetic expansion.  If  parameter  is  a  nameref,
       this  expands  to  the name of the parameter referenced by parameter instead of performing
       the complete indirect expansion.  The exceptions to this are the expansions of ${!prefix*}
       and  ${!name[@]}  described below.  The exclamation point must immediately follow the left
       brace in order to introduce indirection.

       In each of the cases below, word is  subject  to  tilde  expansion,  parameter  expansion,
       command substitution, and arithmetic expansion.

       When not performing substring expansion, using the forms documented below (e.g., :-), bash
       tests for a parameter that is unset or null.  Omitting the colon results in  a  test  only
       for a parameter that is unset.

       ${parameter:-word}
              Use  Default  Values.   If  parameter  is  unset  or null, the expansion of word is
              substituted.  Otherwise, the value of parameter is substituted.
       ${parameter:=word}
              Assign Default Values.  If parameter is unset or null, the  expansion  of  word  is
              assigned  to  parameter.   The  value of parameter is then substituted.  Positional
              parameters and special parameters may not be assigned to in this way.
       ${parameter:?word}
              Display Error if Null or Unset.  If parameter is null or unset,  the  expansion  of
              word  (or  a  message  to  that  effect  if  word is not present) is written to the
              standard error and the shell, if it is  not  interactive,  exits.   Otherwise,  the
              value of parameter is substituted.
       ${parameter:+word}
              Use  Alternate  Value.   If  parameter  is  null  or unset, nothing is substituted,
              otherwise the expansion of word is substituted.
       ${parameter:offset}
       ${parameter:offset:length}
              Substring Expansion.  Expands to up to length characters of the value of  parameter
              starting  at the character specified by offset.  If parameter is @ or *, an indexed
              array subscripted by @ or *, or an associative array name, the  results  differ  as
              described  below.   If  length is omitted, expands to the substring of the value of
              parameter starting at the character specified by offset and extending to the end of
              the value.  length and offset are arithmetic expressions (see ARITHMETIC EVALUATION
              below).

              If offset evaluates to a number less than zero, the value is used as an  offset  in
              characters from the end of the value of parameter.  If length evaluates to a number
              less than zero, it is interpreted as an offset in characters from the  end  of  the
              value  of  parameter  rather  than a number of characters, and the expansion is the
              characters between offset and that result.  Note that a  negative  offset  must  be
              separated  from the colon by at least one space to avoid being confused with the :-
              expansion.

              If parameter is @ or *, the result is length  positional  parameters  beginning  at
              offset.   A  negative  offset  is  taken  relative to one greater than the greatest
              positional parameter,  so  an  offset  of  -1  evaluates  to  the  last  positional
              parameter.   It  is  an  expansion  error if length evaluates to a number less than
              zero.

              If parameter is an indexed array name subscripted by @ or  *,  the  result  is  the
              length members of the array beginning with ${parameter[offset]}.  A negative offset
              is taken relative to one greater than the maximum index of the specified array.  It
              is an expansion error if length evaluates to a number less than zero.

              Substring expansion applied to an associative array produces undefined results.

              Substring  indexing  is  zero-based  unless  the positional parameters are used, in
              which case the indexing starts at 1 by default.  If offset is 0, and the positional
              parameters are used, $0 is prefixed to the list.

       ${!prefix*}
       ${!prefix@}
              Names  matching  prefix.   Expands to the names of variables whose names begin with
              prefix, separated by the first character of the IFS special variable.   When  @  is
              used  and the expansion appears within double quotes, each variable name expands to
              a separate word.

       ${!name[@]}
       ${!name[*]}
              List of array keys.  If name is an array variable, expands to  the  list  of  array
              indices  (keys) assigned in name.  If name is not an array, expands to 0 if name is
              set and null otherwise.  When @ is used and the  expansion  appears  within  double
              quotes, each key expands to a separate word.

       ${#parameter}
              Parameter  length.   The  length  in  characters  of  the  value  of  parameter  is
              substituted.  If parameter is * or @,  the  value  substituted  is  the  number  of
              positional  parameters.   If  parameter is an array name subscripted by * or @, the
              value substituted is the number of elements in  the  array.   If  parameter  is  an
              indexed  array name subscripted by a negative number, that number is interpreted as
              relative to one greater than the maximum index of parameter,  so  negative  indices
              count  back  from  the  end  of  the  array, and an index of -1 references the last
              element.

       ${parameter#word}
       ${parameter##word}
              Remove matching prefix pattern.  The word is expanded to produce a pattern just  as
              in  pathname  expansion,  and matched against the expanded value of parameter using
              the rules described under Pattern Matching  below.   If  the  pattern  matches  the
              beginning  of  the  value  of  parameter,  then  the result of the expansion is the
              expanded value of parameter with the shortest matching pattern (the ``#'' case)  or
              the  longest  matching  pattern (the ``##'' case) deleted.  If parameter is @ or *,
              the pattern removal operation is applied to each positional parameter in turn,  and
              the expansion is the resultant list.  If parameter is an array variable subscripted
              with @ or *, the pattern removal operation is applied to each member of  the  array
              in turn, and the expansion is the resultant list.

       ${parameter%word}
       ${parameter%%word}
              Remove  matching suffix pattern.  The word is expanded to produce a pattern just as
              in pathname expansion, and matched against the expanded value  of  parameter  using
              the  rules  described  under  Pattern  Matching  below.   If  the pattern matches a
              trailing portion of the expanded  value  of  parameter,  then  the  result  of  the
              expansion  is  the  expanded  value of parameter with the shortest matching pattern
              (the ``%'' case) or the longest matching pattern (the  ``%%''  case)  deleted.   If
              parameter  is  @  or *, the pattern removal operation is applied to each positional
              parameter in turn, and the expansion is the resultant list.   If  parameter  is  an
              array variable subscripted with @ or *, the pattern removal operation is applied to
              each member of the array in turn, and the expansion is the resultant list.

       ${parameter/pattern/string}
       ${parameter//pattern/string}
       ${parameter/#pattern/string}
       ${parameter/%pattern/string}
              Pattern substitution.  The pattern is expanded to produce  a  pattern  just  as  in
              pathname expansion.  Parameter is expanded and the longest match of pattern against
              its value is replaced with string.  string undergoes tilde expansion, parameter and
              variable  expansion,  arithmetic  expansion,  command and process substitution, and
              quote removal.  The match is performed using  the  rules  described  under  Pattern
              Matching  below.   In  the  first form above, only the first match is replaced.  If
              there are two slashes separating parameter and pattern (the second form above), all
              matches  of  pattern  are  replaced  with string.  If pattern is preceded by # (the
              third form above), it must  match  at  the  beginning  of  the  expanded  value  of
              parameter.   If  pattern is preceded by % (the fourth form above), it must match at
              the end of the expanded value of parameter.  If the expansion of  string  is  null,
              matches  of pattern are deleted.  If string is null, matches of pattern are deleted
              and the / following pattern may be omitted.

              If the patsub_replacement  shell  option  is  enabled  using  shopt,  any  unquoted
              instances of & in string are replaced with the matching portion of pattern.

              Quoting  any  part  of  string  inhibits replacement in the expansion of the quoted
              portion, including replacement strings stored in shell variables.   Backslash  will
              escape  & in string; the backslash is removed in order to permit a literal & in the
              replacement string.  Backslash can also be used to escape a backslash;  \\  results
              in  a  literal  backslash  in the replacement.  Users should take care if string is
              double-quoted to avoid unwanted interactions  between  the  backslash  and  double-
              quoting,  since  backslash  has  special  meaning  within  double  quotes.  Pattern
              substitution performs the check  for  unquoted  &  after  expanding  string;  shell
              programmers  should  quote  any occurrences of & they want to be taken literally in
              the replacement and ensure any  instances  of  &  they  want  to  be  replaced  are
              unquoted.

              If  the  nocasematch shell option is enabled, the match is performed without regard
              to the case of alphabetic characters.  If parameter is @  or  *,  the  substitution
              operation is applied to each positional parameter in turn, and the expansion is the
              resultant list.  If parameter is an array variable subscripted with  @  or  *,  the
              substitution  operation  is  applied  to  each member of the array in turn, and the
              expansion is the resultant list.

       ${parameter^pattern}
       ${parameter^^pattern}
       ${parameter,pattern}
       ${parameter,,pattern}
              Case modification.  This expansion modifies the case of  alphabetic  characters  in
              parameter.   The  pattern  is  expanded  to  produce  a pattern just as in pathname
              expansion.  Each character in the expanded value of  parameter  is  tested  against
              pattern, and, if it matches the pattern, its case is converted.  The pattern should
              not attempt to match more than one character.  The ^  operator  converts  lowercase
              letters  matching  pattern to uppercase; the , operator converts matching uppercase
              letters to lowercase.  The ^^ and ,, expansions convert each matched  character  in
              the  expanded  value;  the  ^  and  ,  expansions  match and convert only the first
              character in the expanded value.  If pattern is omitted, it is treated  like  a  ?,
              which  matches  every  character.   If  parameter  is @ or *, the case modification
              operation is applied to each positional parameter in turn, and the expansion is the
              resultant  list.   If  parameter  is an array variable subscripted with @ or *, the
              case modification operation is applied to each member of the array in turn, and the
              expansion is the resultant list.

       ${parameter@operator}
              Parameter transformation.  The expansion is either a transformation of the value of
              parameter or  information  about  parameter  itself,  depending  on  the  value  of
              operator.  Each operator is a single letter:

              U      The  expansion  is  a  string  that is the value of parameter with lowercase
                     alphabetic characters converted to uppercase.
              u      The expansion is a string that is the value  of  parameter  with  the  first
                     character converted to uppercase, if it is alphabetic.
              L      The  expansion  is  a  string  that is the value of parameter with uppercase
                     alphabetic characters converted to lowercase.
              Q      The expansion is a string that is the value of parameter quoted in a  format
                     that can be reused as input.
              E      The  expansion  is  a  string  that is the value of parameter with backslash
                     escape sequences expanded as with the $'...' quoting mechanism.
              P      The expansion is a string that is the  result  of  expanding  the  value  of
                     parameter as if it were a prompt string (see PROMPTING below).
              A      The  expansion is a string in the form of an assignment statement or declare
                     command that, if evaluated, will recreate parameter with its attributes  and
                     value.
              K      Produces a possibly-quoted version of the value of parameter, except that it
                     prints the values of indexed and associative arrays as a sequence of  quoted
                     key-value pairs (see Arrays above).
              a      The expansion is a string consisting of flag values representing parameter's
                     attributes.
              k      Like the K transformation, but expands the keys and values  of  indexed  and
                     associative arrays to separate words after word splitting.

              If  parameter  is  @ or *, the operation is applied to each positional parameter in
              turn, and the expansion is the resultant list.  If parameter is an  array  variable
              subscripted  with  @  or *, the operation is applied to each member of the array in
              turn, and the expansion is the resultant list.

              The result of the expansion is subject to word splitting and pathname expansion  as
              described below.

   Command Substitution
       Command  substitution  allows  the output of a command to replace the command name.  There
       are two forms:

              $(command)
       or
              `command`

       Bash performs the expansion by executing command in a subshell environment  and  replacing
       the  command  substitution  with  the  standard  output  of the command, with any trailing
       newlines deleted.  Embedded newlines are not deleted, but they may be removed during  word
       splitting.   The  command  substitution  $(cat file) can be replaced by the equivalent but
       faster $(< file).

       When the old-style backquote form of substitution is used, backslash retains  its  literal
       meaning  except  when  followed  by  $,  `,  or  \.  The first backquote not preceded by a
       backslash terminates the command  substitution.   When  using  the  $(command)  form,  all
       characters between the parentheses make up the command; none are treated specially.

       Command  substitutions  may be nested.  To nest when using the backquoted form, escape the
       inner backquotes with backslashes.

       If the substitution appears within double quotes, word splitting  and  pathname  expansion
       are not performed on the results.

   Arithmetic Expansion
       Arithmetic   expansion   allows  the  evaluation  of  an  arithmetic  expression  and  the
       substitution of the result.  The format for arithmetic expansion is:

              $((expression))

       The old format $[expression] is deprecated and will be removed  in  upcoming  versions  of
       bash.

       The  expression  undergoes  the  same  expansions  as if it were within double quotes, but
       double quote characters in expression are not treated  specially  and  are  removed.   All
       tokens  in  the expression undergo parameter and variable expansion, command substitution,
       and quote removal.  The result is treated as the arithmetic expression  to  be  evaluated.
       Arithmetic expansions may be nested.

       The  evaluation  is  performed  according  to  the  rules  listed  below  under ARITHMETIC
       EVALUATION.  If expression is invalid, bash prints a message  indicating  failure  and  no
       substitution occurs.

   Process Substitution
       Process  substitution  allows  a  process's  input  or  output  to  be referred to using a
       filename.   It  takes  the  form  of  <(list)  or  >(list).   The  process  list  is   run
       asynchronously, and its input or output appears as a filename.  This filename is passed as
       an argument to the current command as the result of the expansion.  If the >(list) form is
       used,  writing  to the file will provide input for list.  If the <(list) form is used, the
       file passed as an argument  should  be  read  to  obtain  the  output  of  list.   Process
       substitution  is  supported  on  systems  that  support named pipes (FIFOs) or the /dev/fd
       method of naming open files.

       When available, process  substitution  is  performed  simultaneously  with  parameter  and
       variable expansion, command substitution, and arithmetic expansion.

   Word Splitting
       The  shell  scans the results of parameter expansion, command substitution, and arithmetic
       expansion that did not occur within double quotes for word splitting.

       The shell treats each character of IFS as a delimiter, and splits the results of the other
       expansions  into  words  using these characters as field terminators.  If IFS is unset, or
       its value is exactly <space><tab><newline>, the default, then sequences of <space>, <tab>,
       and  <newline>  at  the  beginning  and  end of the results of the previous expansions are
       ignored, and any sequence of IFS characters not at the beginning or end serves to  delimit
       words.   If  IFS  has  a  value  other  than the default, then sequences of the whitespace
       characters space, tab, and newline are ignored at the beginning and end of  the  word,  as
       long  as  the  whitespace  character is in the value of IFS (an IFS whitespace character).
       Any character in IFS that is not IFS whitespace, along with any  adjacent  IFS  whitespace
       characters,  delimits a field.  A sequence of IFS whitespace characters is also treated as
       a delimiter.  If the value of IFS is null, no word splitting occurs.

       Explicit null arguments ("" or '') are retained and passed to commands as  empty  strings.
       Unquoted  implicit null arguments, resulting from the expansion of parameters that have no
       values, are removed.  If a parameter with no value is expanded  within  double  quotes,  a
       null  argument results and is retained and passed to a command as an empty string.  When a
       quoted null argument appears as part of a word  whose  expansion  is  non-null,  the  null
       argument  is  removed.   That  is,  the word -d'' becomes -d after word splitting and null
       argument removal.

       Note that if no expansion occurs, no splitting is performed.

   Pathname Expansion
       After word splitting, unless the -f option has been set, bash  scans  each  word  for  the
       characters  *,  ?, and [.  If one of these characters appears, and is not quoted, then the
       word is regarded as a  pattern,  and  replaced  with  an  alphabetically  sorted  list  of
       filenames matching the pattern (see Pattern Matching below).  If no matching filenames are
       found, and the shell option nullglob is not enabled, the word is left unchanged.   If  the
       nullglob  option  is  set, and no matches are found, the word is removed.  If the failglob
       shell option is set, and no matches are found, an error message is printed and the command
       is  not  executed.   If  the  shell  option  nocaseglob is enabled, the match is performed
       without regard to  the  case  of  alphabetic  characters.   Note  that  when  using  range
       expressions  like  [a-z] (see below), letters of the other case may be included, depending
       on the setting of LC_COLLATE.   When  a  pattern  is  used  for  pathname  expansion,  the
       character  ``.''   at the start of a name or immediately following a slash must be matched
       explicitly, unless the shell option dotglob is set.  In order to match the filenames ``.''
       and  ``..'',  the  pattern must begin with ``.'' (for example, ``.?''), even if dotglob is
       set.  If the globskipdots shell option is enabled, the filenames ``.''   and  ``..''   are
       never  matched, even if the pattern begins with a ``.''.  When not matching pathnames, the
       ``.''  character is not treated specially.  When matching a pathname, the slash  character
       must  always  be  matched  explicitly  by  a  slash  in the pattern, but in other matching
       contexts it can be matched by a special pattern character as described below under Pattern
       Matching.   See  the  description  of  shopt  below  under  SHELL  BUILTIN  COMMANDS for a
       description of  the  nocaseglob,  nullglob,  globskipdots,  failglob,  and  dotglob  shell
       options.

       The  GLOBIGNORE  shell  variable  may be used to restrict the set of file names matching a
       pattern.  If GLOBIGNORE is set, each matching file name  that  also  matches  one  of  the
       patterns  in  GLOBIGNORE is removed from the list of matches.  If the nocaseglob option is
       set, the matching against the patterns in GLOBIGNORE is performed without regard to  case.
       The  filenames  ``.''  and ``..''  are always ignored when GLOBIGNORE is set and not null.
       However, setting GLOBIGNORE to a non-null value has the effect  of  enabling  the  dotglob
       shell  option,  so all other filenames beginning with a ``.''  will match.  To get the old
       behavior of ignoring filenames beginning with a ``.'', make ``.*''  one of the patterns in
       GLOBIGNORE.   The  dotglob  option  is  disabled  when  GLOBIGNORE  is unset.  The pattern
       matching honors the setting of the extglob shell option.

       Pattern Matching

       Any character that appears in  a  pattern,  other  than  the  special  pattern  characters
       described  below,  matches  itself.   The  NUL  character  may  not occur in a pattern.  A
       backslash escapes the following  character;  the  escaping  backslash  is  discarded  when
       matching.   The  special  pattern  characters  must  be  quoted  if they are to be matched
       literally.

       The special pattern characters have the following meanings:

              *      Matches any string, including the null  string.   When  the  globstar  shell
                     option  is  enabled,  and  *  is  used  in a pathname expansion context, two
                     adjacent *s used as a single pattern will match all files and zero  or  more
                     directories  and  subdirectories.   If followed by a /, two adjacent *s will
                     match only directories and subdirectories.
              ?      Matches any single character.
              [...]  Matches any one of the enclosed characters.  A pair of characters  separated
                     by  a  hyphen  denotes  a range expression; any character that falls between
                     those two  characters,  inclusive,  using  the  current  locale's  collating
                     sequence  and  character  set, is matched.  If the first character following
                     the [ is a !  or a ^ then  any  character  not  enclosed  is  matched.   The
                     sorting  order  of  characters  in  range  expressions,  and  the characters
                     included in the range, are determined by the current locale and  the  values
                     of  the  LC_COLLATE  or  LC_ALL  shell  variables,  if  set.   To obtain the
                     traditional interpretation of range expressions, where [a-d]  is  equivalent
                     to  [abcd],  set  value  of  the  LC_ALL  shell variable to C, or enable the
                     globasciiranges shell option.  A - may be matched by  including  it  as  the
                     first  or  last character in the set.  A ] may be matched by including it as
                     the first character in the set.

                     Within [ and  ],  character  classes  can  be  specified  using  the  syntax
                     [:class:],  where class is one of the following classes defined in the POSIX
                     standard:
                     alnum alpha ascii blank cntrl digit graph lower print punct space upper word
                     xdigit
                     A  character  class matches any character belonging to that class.  The word
                     character class matches letters, digits, and the character _.

                     Within [ and ], an equivalence class  can  be  specified  using  the  syntax
                     [=c=],  which  matches  all  characters  with  the same collation weight (as
                     defined by the current locale) as the character c.

                     Within [ and ], the syntax [.symbol.] matches the collating symbol symbol.

       If the extglob shell option is enabled using  the  shopt  builtin,  the  shell  recognizes
       several extended pattern matching operators.  In the following description, a pattern-list
       is a list of one or more patterns separated by a |.   Composite  patterns  may  be  formed
       using one or more of the following sub-patterns:

              ?(pattern-list)
                     Matches zero or one occurrence of the given patterns
              *(pattern-list)
                     Matches zero or more occurrences of the given patterns
              +(pattern-list)
                     Matches one or more occurrences of the given patterns
              @(pattern-list)
                     Matches one of the given patterns
              !(pattern-list)
                     Matches anything except one of the given patterns

       Theextglob  option  changes the behavior of the parser, since the parentheses are normally
       treated as operators with syntactic meaning.  To ensure that  extended  matching  patterns
       are  parsed  correctly,  make  sure  that  extglob  is  enabled  before parsing constructs
       containing the patterns, including shell functions and command substitutions.

       When matching filenames, the dotglob shell option determines the set of filenames that are
       tested:  when  dotglob  is enabled, the set of filenames includes all files beginning with
       ``.'', but ``.'' and ``..'' must be matched by a pattern or sub-pattern that begins with a
       dot;  when  it  is  disabled,  the set does not include any filenames beginning with ``.''
       unless the pattern or sub-pattern begins with a ``.''.  As above, ``.'' only has a special
       meaning when matching filenames.

       Complicated  extended  pattern  matching against long strings is slow, especially when the
       patterns contain alternations and the strings contain multiple  matches.   Using  separate
       matches  against  shorter  strings,  or  using  arrays of strings instead of a single long
       string, may be faster.

   Quote Removal
       After the preceding expansions, all unquoted occurrences of the characters  \,  ',  and  "
       that did not result from one of the above expansions are removed.

REDIRECTION

       Before  a  command  is  executed,  its  input and output may be redirected using a special
       notation interpreted by the shell.   Redirection  allows  commands'  file  handles  to  be
       duplicated, opened, closed, made to refer to different files, and can change the files the
       command reads from and writes to.  Redirection may also be used to modify file handles  in
       the  current shell execution environment.  The following redirection operators may precede
       or appear anywhere within a simple command or may  follow  a  command.   Redirections  are
       processed in the order they appear, from left to right.

       Each  redirection that may be preceded by a file descriptor number may instead be preceded
       by a word of the form {varname}.  In this case, for each redirection operator  except  >&-
       and  <&-, the shell will allocate a file descriptor greater than or equal to 10 and assign
       it to varname.  If >&- or <&- is preceded by {varname}, the value of varname  defines  the
       file  descriptor  to close.  If {varname} is supplied, the redirection persists beyond the
       scope of the command, allowing the  shell  programmer  to  manage  the  file  descriptor's
       lifetime manually.  The varredir_close shell option manages this behavior.

       In  the  following  descriptions,  if the file descriptor number is omitted, and the first
       character of the redirection operator is <, the redirection refers to the  standard  input
       (file  descriptor  0).   If  the  first  character  of  the redirection operator is >, the
       redirection refers to the standard output (file descriptor 1).

       The word  following  the  redirection  operator  in  the  following  descriptions,  unless
       otherwise  noted, is subjected to brace expansion, tilde expansion, parameter and variable
       expansion, command substitution, arithmetic expansion, quote removal, pathname  expansion,
       and word splitting.  If it expands to more than one word, bash reports an error.

       Note that the order of redirections is significant.  For example, the command

              ls > dirlist 2>&1

       directs both standard output and standard error to the file dirlist, while the command

              ls 2>&1 > dirlist

       directs  only  the  standard  output  to  file  dirlist,  because  the  standard error was
       duplicated from the standard output before the standard output was redirected to dirlist.

       Bash handles several filenames specially when they are used in redirections, as  described
       in  the  following table.  If the operating system on which bash is running provides these
       special files, bash will use them; otherwise it will  emulate  them  internally  with  the
       behavior described below.

              /dev/fd/fd
                     If fd is a valid integer, file descriptor fd is duplicated.
              /dev/stdin
                     File descriptor 0 is duplicated.
              /dev/stdout
                     File descriptor 1 is duplicated.
              /dev/stderr
                     File descriptor 2 is duplicated.
              /dev/tcp/host/port
                     If host is a valid hostname or Internet address, and port is an integer port
                     number or service name, bash attempts to open the corresponding TCP socket.
              /dev/udp/host/port
                     If host is a valid hostname or Internet address, and port is an integer port
                     number or service name, bash attempts to open the corresponding UDP socket.

       A failure to open or create a file causes the redirection to fail.

       Redirections  using  file descriptors greater than 9 should be used with care, as they may
       conflict with file descriptors the shell uses internally.

       Note that the exec builtin command can make redirections take effect in the current shell.

   Redirecting Input
       Redirection of input causes the file whose name results from the expansion of word  to  be
       opened for reading on file descriptor n, or the standard input (file descriptor 0) if n is
       not specified.

       The general format for redirecting input is:

              [n]<word

   Redirecting Output
       Redirection of output causes the file whose name results from the expansion of word to  be
       opened  for  writing on file descriptor n, or the standard output (file descriptor 1) if n
       is not specified.  If the file does not exist it is  created;  if  it  does  exist  it  is
       truncated to zero size.

       The general format for redirecting output is:

              [n]>word

       If  the  redirection  operator  is >, and the noclobber option to the set builtin has been
       enabled, the redirection will fail if the file whose name results from  the  expansion  of
       word  exists and is a regular file.  If the redirection operator is >|, or the redirection
       operator is > and the noclobber option to the set builtin  command  is  not  enabled,  the
       redirection is attempted even if the file named by word exists.

   Appending Redirected Output
       Redirection  of  output  in  this  fashion  causes  the  file  whose name results from the
       expansion of word to be opened for appending on file descriptor n, or the standard  output
       (file descriptor 1) if n is not specified.  If the file does not exist it is created.

       The general format for appending output is:

              [n]>>word

   Redirecting Standard Output and Standard Error
       This  construct allows both the standard output (file descriptor 1) and the standard error
       output (file descriptor 2) to be redirected to the file whose name  is  the  expansion  of
       word.

       There are two formats for redirecting standard output and standard error:

              &>word
       and
              >&word

       Of the two forms, the first is preferred.  This is semantically equivalent to

              >word 2>&1

       When  using  the  second  form,  word  may not expand to a number or -.  If it does, other
       redirection operators apply (see Duplicating File  Descriptors  below)  for  compatibility
       reasons.

   Appending Standard Output and Standard Error
       This  construct allows both the standard output (file descriptor 1) and the standard error
       output (file descriptor 2) to be appended to the file whose name is the expansion of word.

       The format for appending standard output and standard error is:

              &>>word

       This is semantically equivalent to

              >>word 2>&1

       (see Duplicating File Descriptors below).

   Here Documents
       This type of redirection instructs the shell to read input from the current source until a
       line  containing  only delimiter (with no trailing blanks) is seen.  All of the lines read
       up to that point are then used as the standard  input  (or  file  descriptor  n  if  n  is
       specified) for a command.

       The format of here-documents is:

              [n]<<[-]word
                      here-document
              delimiter

       No  parameter  and  variable  expansion,  command  substitution,  arithmetic expansion, or
       pathname expansion is performed on word.  If any part of word is quoted, the delimiter  is
       the  result of quote removal on word, and the lines in the here-document are not expanded.
       If word is unquoted, all lines of the here-document are subjected to parameter  expansion,
       command  substitution,  and  arithmetic  expansion,  the  character sequence \<newline> is
       ignored, and \ must be used to quote the characters \, $, and `.

       If the redirection operator is <<-, then all leading  tab  characters  are  stripped  from
       input  lines  and  the line containing delimiter.  This allows here-documents within shell
       scripts to be indented in a natural fashion.

   Here Strings
       A variant of here documents, the format is:

              [n]<<<word

       The  word  undergoes  tilde  expansion,  parameter   and   variable   expansion,   command
       substitution,  arithmetic  expansion,  and  quote  removal.   Pathname  expansion and word
       splitting are not performed.  The result is supplied as a single string,  with  a  newline
       appended, to the command on its standard input (or file descriptor n if n is specified).

   Duplicating File Descriptors
       The redirection operator

              [n]<&word

       is  used  to duplicate input file descriptors.  If word expands to one or more digits, the
       file descriptor denoted by n is made to be a copy of that file descriptor.  If the  digits
       in  word  do not specify a file descriptor open for input, a redirection error occurs.  If
       word evaluates to -, file descriptor n is closed.  If n is  not  specified,  the  standard
       input (file descriptor 0) is used.

       The operator

              [n]>&word

       is  used  similarly  to  duplicate  output  file  descriptors.  If n is not specified, the
       standard output (file descriptor 1) is used.  If the digits in word do not specify a  file
       descriptor  open  for  output,  a  redirection error occurs.  If word evaluates to -, file
       descriptor n is closed.  As a special case, if n is omitted, and word does not  expand  to
       one  or  more  digits  or  -,  the  standard  output  and standard error are redirected as
       described previously.

   Moving File Descriptors
       The redirection operator

              [n]<&digit-

       moves the file descriptor digit  to  file  descriptor  n,  or  the  standard  input  (file
       descriptor 0) if n is not specified.  digit is closed after being duplicated to n.

       Similarly, the redirection operator

              [n]>&digit-

       moves  the  file  descriptor  digit  to  file  descriptor  n, or the standard output (file
       descriptor 1) if n is not specified.

   Opening File Descriptors for Reading and Writing
       The redirection operator

              [n]<>word

       causes the file whose name is the expansion of word to be  opened  for  both  reading  and
       writing  on file descriptor n, or on file descriptor 0 if n is not specified.  If the file
       does not exist, it is created.

ALIASES

       Aliases allow a string to be substituted for a word when it is used as the first word of a
       simple  command.  The shell maintains a list of aliases that may be set and unset with the
       alias and unalias builtin commands (see SHELL BUILTIN COMMANDS below).  The first word  of
       each  simple command, if unquoted, is checked to see if it has an alias.  If so, that word
       is replaced by the text of the alias.  The characters /, $, `, and = and any of the  shell
       metacharacters  or  quoting  characters listed above may not appear in an alias name.  The
       replacement text may contain any valid shell input, including shell  metacharacters.   The
       first  word of the replacement text is tested for aliases, but a word that is identical to
       an alias being expanded is not expanded a second time.  This means that one may  alias  ls
       to  ls -F, for instance, and bash does not try to recursively expand the replacement text.
       If the last character of the alias value is a blank, then the next command word  following
       the alias is also checked for alias expansion.

       Aliases  are  created  and  listed  with  the  alias command, and removed with the unalias
       command.

       There is no mechanism for using arguments in  the  replacement  text.   If  arguments  are
       needed, use a shell function (see FUNCTIONS below).

       Aliases  are  not  expanded  when  the shell is not interactive, unless the expand_aliases
       shell option is set using shopt (see the description of shopt under SHELL BUILTIN COMMANDS
       below).

       The  rules  concerning  the  definition  and  use of aliases are somewhat confusing.  Bash
       always reads at least one complete line of input, and all lines that make  up  a  compound
       command,  before  executing  any  of  the  commands  on that line or the compound command.
       Aliases are expanded when a command is read, not when it is executed.  Therefore, an alias
       definition  appearing  on  the same line as another command does not take effect until the
       next line of input is read.  The commands following the alias definition on that line  are
       not  affected  by  the  new  alias.   This  behavior  is  also an issue when functions are
       executed.  Aliases are expanded when a function definition is read, not when the  function
       is executed, because a function definition is itself a command.  As a consequence, aliases
       defined in a function are not available until after that  function  is  executed.   To  be
       safe,  always  put  alias definitions on a separate line, and do not use alias in compound
       commands.

       For almost every purpose, aliases are superseded by shell functions.

FUNCTIONS

       A shell function, defined as described above under  SHELL  GRAMMAR,  stores  a  series  of
       commands  for  later  execution.   When  the  name of a shell function is used as a simple
       command name, the list of  commands  associated  with  that  function  name  is  executed.
       Functions  are  executed in the context of the current shell; no new process is created to
       interpret them (contrast this with the execution of a shell script).  When a  function  is
       executed,  the  arguments  to  the  function  become  the positional parameters during its
       execution.  The special parameter # is updated to reflect the change.  Special parameter 0
       is  unchanged.   The  first  element  of  the  FUNCNAME variable is set to the name of the
       function while the function is executing.

       All other aspects of the shell execution environment are identical between a function  and
       its  caller  with these exceptions: the DEBUG and RETURN traps (see the description of the
       trap builtin under SHELL BUILTIN COMMANDS below) are not inherited unless the function has
       been  given  the trace attribute (see the description of the declare builtin below) or the
       -o functrace shell option has been enabled  with  the  set  builtin  (in  which  case  all
       functions  inherit  the  DEBUG and RETURN traps), and the ERR trap is not inherited unless
       the -o errtrace shell option has been enabled.

       Variables local to the function may be declared with  the  local  builtin  command  (local
       variables).   Ordinarily,  variables  and their values are shared between the function and
       its caller.  If a variable is declared local, the variable's visible scope  is  restricted
       to that function and its children (including the functions it calls).

       In  the  following  description,  the  current  scope  is a currently- executing function.
       Previous scopes consist of that function's caller and so on, back to the  "global"  scope,
       where  the  shell  is not executing any shell function.  Consequently, a local variable at
       the current scope is a variable declared using  the  local  or  declare  builtins  in  the
       function that is currently executing.

       Local  variables  "shadow"  variables with the same name declared at previous scopes.  For
       instance, a local variable declared in a function hides a  global  variable  of  the  same
       name:  references and assignments refer to the local variable, leaving the global variable
       unmodified.  When the function returns, the global variable is once again visible.

       The shell uses dynamic scoping to control a variable's visibility within functions.   With
       dynamic  scoping,  visible  variables  and  their  values  are a result of the sequence of
       function calls that caused execution to reach  the  current  function.   The  value  of  a
       variable that a function sees depends on its value within its caller, if any, whether that
       caller is the "global" scope or another shell function.  This is also  the  value  that  a
       local  variable  declaration  "shadows",  and the value that is restored when the function
       returns.

       For example, if a variable var is declared as local in function  func1,  and  func1  calls
       another function func2, references to var made from within func2 will resolve to the local
       variable var from func1, shadowing any global variable named var.

       The unset builtin also acts using the same dynamic scope: if a variable is  local  to  the
       current  scope,  unset will unset it; otherwise the unset will refer to the variable found
       in any calling scope as described above.  If a variable at  the  current  local  scope  is
       unset, it will remain so (appearing as unset) until it is reset in that scope or until the
       function returns.  Once the function returns, any instance of the variable at  a  previous
       scope  will  become  visible.   If  the  unset acts on a variable at a previous scope, any
       instance of a variable with that name that had been  shadowed  will  become  visible  (see
       below how the localvar_unset shell option changes this behavior).

       The  FUNCNEST  variable,  if  set  to  a  numeric  value greater than 0, defines a maximum
       function nesting level.  Function invocations that  exceed  the  limit  cause  the  entire
       command to abort.

       If  the  builtin  command  return  is  executed  in a function, the function completes and
       execution resumes with the next command after the function call.  Any  command  associated
       with the RETURN trap is executed before execution resumes.  When a function completes, the
       values of the positional parameters and the special parameter # are restored to the values
       they had prior to the function's execution.

       Function  names and definitions may be listed with the -f option to the declare or typeset
       builtin commands.  The -F option to declare or typeset will list the function  names  only
       (and optionally the source file and line number, if the extdebug shell option is enabled).
       Functions may be exported so that child shell processes (those created  when  executing  a
       separate  shell  invocation)  automatically  have  them  defined with the -f option to the
       export builtin.  A function definition may be deleted using the -f  option  to  the  unset
       builtin.

       Functions  may  be recursive.  The FUNCNEST variable may be used to limit the depth of the
       function call stack and restrict the number of function invocations.  By default, no limit
       is imposed on the number of recursive calls.

ARITHMETIC EVALUATION

       The  shell allows arithmetic expressions to be evaluated, under certain circumstances (see
       the let and declare builtin commands, the (( compound command, and Arithmetic  Expansion).
       Evaluation  is done in fixed-width integers with no check for overflow, though division by
       0 is trapped and flagged as an error.  The operators and their precedence,  associativity,
       and  values are the same as in the C language.  The following list of operators is grouped
       into levels of equal-precedence operators.  The levels are listed in order  of  decreasing
       precedence.

       id++ id--
              variable post-increment and post-decrement
       - +    unary minus and plus
       ++id --id
              variable pre-increment and pre-decrement
       ! ~    logical and bitwise negation
       **     exponentiation
       * / %  multiplication, division, remainder
       + -    addition, subtraction
       << >>  left and right bitwise shifts
       <= >= < >
              comparison
       == !=  equality and inequality
       &      bitwise AND
       ^      bitwise exclusive OR
       |      bitwise OR
       &&     logical AND
       ||     logical OR
       expr?expr:expr
              conditional operator
       = *= /= %= += -= <<= >>= &= ^= |=
              assignment
       expr1 , expr2
              comma

       Shell  variables  are  allowed  as  operands;  parameter expansion is performed before the
       expression is evaluated.  Within an expression, shell variables may also be referenced  by
       name without using the parameter expansion syntax.  A shell variable that is null or unset
       evaluates to 0 when referenced by name without using the parameter expansion syntax.   The
       value  of  a  variable  is evaluated as an arithmetic expression when it is referenced, or
       when a variable which has been given the integer attribute using declare -i is assigned  a
       value.  A null value evaluates to 0.  A shell variable need not have its integer attribute
       turned on to be used in an expression.

       Integer constants  follow  the  C  language  definition,  without  suffixes  or  character
       constants.   Constants with a leading 0 are interpreted as octal numbers.  A leading 0x or
       0X denotes hexadecimal.  Otherwise, numbers take the form  [base#]n,  where  the  optional
       base  is  a  decimal  number between 2 and 64 representing the arithmetic base, and n is a
       number in that base.  If base# is omitted, then base 10 is used.  When specifying n, if  a
       non-digit is required, the digits greater than 9 are represented by the lowercase letters,
       the uppercase letters, @, and _, in that order.  If base is less  than  or  equal  to  36,
       lowercase  and  uppercase letters may be used interchangeably to represent numbers between
       10 and 35.

       Operators are evaluated in  order  of  precedence.   Sub-expressions  in  parentheses  are
       evaluated first and may override the precedence rules above.

CONDITIONAL EXPRESSIONS

       Conditional  expressions  are  used  by the [[ compound command and the test and [ builtin
       commands to test file attributes and perform string and arithmetic comparisons.  The  test
       and  [  commands  determine  their  behavior  based  on  the  number of arguments; see the
       descriptions of those commands for any other command-specific actions.

       Expressions are formed from the following unary or binary primaries.  Bash handles several
       filenames  specially  when they are used in expressions.  If the operating system on which
       bash is running provides these special files,  bash  will  use  them;  otherwise  it  will
       emulate  them  internally with this behavior: If any file argument to one of the primaries
       is of the form /dev/fd/n, then file descriptor n is checked.  If the file argument to  one
       of  the primaries is one of /dev/stdin, /dev/stdout, or /dev/stderr, file descriptor 0, 1,
       or 2, respectively, is checked.

       Unless otherwise specified, primaries that operate on  files  follow  symbolic  links  and
       operate on the target of the link, rather than the link itself.

       When  used with [[, the < and > operators sort lexicographically using the current locale.
       The test command sorts using ASCII ordering.

       -a file
              True if file exists.
       -b file
              True if file exists and is a block special file.
       -c file
              True if file exists and is a character special file.
       -d file
              True if file exists and is a directory.
       -e file
              True if file exists.
       -f file
              True if file exists and is a regular file.
       -g file
              True if file exists and is set-group-id.
       -h file
              True if file exists and is a symbolic link.
       -k file
              True if file exists and its ``sticky'' bit is set.
       -p file
              True if file exists and is a named pipe (FIFO).
       -r file
              True if file exists and is readable.
       -s file
              True if file exists and has a size greater than zero.
       -t fd  True if file descriptor fd is open and refers to a terminal.
       -u file
              True if file exists and its set-user-id bit is set.
       -w file
              True if file exists and is writable.
       -x file
              True if file exists and is executable.
       -G file
              True if file exists and is owned by the effective group id.
       -L file
              True if file exists and is a symbolic link.
       -N file
              True if file exists and has been modified since it was last read.
       -O file
              True if file exists and is owned by the effective user id.
       -S file
              True if file exists and is a socket.
       file1 -ef file2
              True if file1 and file2 refer to the same device and inode numbers.
       file1 -nt file2
              True if file1 is newer (according to modification date) than  file2,  or  if  file1
              exists and file2 does not.
       file1 -ot file2
              True if file1 is older than file2, or if file2 exists and file1 does not.
       -o optname
              True  if  the  shell  option optname is enabled.  See the list of options under the
              description of the -o option to the set builtin below.
       -v varname
              True if the shell variable varname is set (has been assigned a value).
       -R varname
              True if the shell variable varname is set and is a name reference.
       -z string
              True if the length of string is zero.
       string
       -n string
              True if the length of string is non-zero.

       string1 == string2
       string1 = string2
              True if the strings are equal.  = should be used with the test  command  for  POSIX
              conformance.   When  used  with  the  [[ command, this performs pattern matching as
              described above (Compound Commands).

       string1 != string2
              True if the strings are not equal.

       string1 < string2
              True if string1 sorts before string2 lexicographically.

       string1 > string2
              True if string1 sorts after string2 lexicographically.

       arg1 OP arg2
              OP is one of -eq, -ne, -lt, -le, -gt, or -ge.  These  arithmetic  binary  operators
              return  true  if  arg1 is equal to, not equal to, less than, less than or equal to,
              greater than, or greater than or equal to arg2, respectively.  Arg1 and arg2 may be
              positive  or  negative  integers.  When used with the [[ command, Arg1 and Arg2 are
              evaluated as arithmetic expressions (see ARITHMETIC EVALUATION above).

SIMPLE COMMAND EXPANSION

       When  a  simple  command  is  executed,  the  shell  performs  the  following  expansions,
       assignments, and redirections, from left to right, in the following order.

       1.     The  words  that the parser has marked as variable assignments (those preceding the
              command name) and redirections are saved for later processing.

       2.     The words that are not variable assignments or redirections are expanded.   If  any
              words remain after expansion, the first word is taken to be the name of the command
              and the remaining words are the arguments.

       3.     Redirections are performed as described above under REDIRECTION.

       4.     The text after the  =  in  each  variable  assignment  undergoes  tilde  expansion,
              parameter  expansion, command substitution, arithmetic expansion, and quote removal
              before being assigned to the variable.

       If no command name results, the variable assignments affect the current shell environment.
       In  the  case  of  such  a  command  (one  that consists only of assignment statements and
       redirections), assignment statements are performed before  redirections.   Otherwise,  the
       variables  are  added  to  the  environment  of the executed command and do not affect the
       current shell environment.  If any of the assignments attempts to  assign  a  value  to  a
       readonly variable, an error occurs, and the command exits with a non-zero status.

       If  no  command  name  results,  redirections are performed, but do not affect the current
       shell environment.  A redirection error causes the command to exit with a non-zero status.

       If there is a command name left after expansion, execution proceeds  as  described  below.
       Otherwise,  the command exits.  If one of the expansions contained a command substitution,
       the exit status of the command is  the  exit  status  of  the  last  command  substitution
       performed.   If  there  were  no command substitutions, the command exits with a status of
       zero.

COMMAND EXECUTION

       After a command has been split into words, if it  results  in  a  simple  command  and  an
       optional list of arguments, the following actions are taken.

       If the command name contains no slashes, the shell attempts to locate it.  If there exists
       a shell function by that name, that function is invoked as described above  in  FUNCTIONS.
       If  the  name  does  not  match a function, the shell searches for it in the list of shell
       builtins.  If a match is found, that builtin is invoked.

       If the name is neither a shell function nor a  builtin,  and  contains  no  slashes,  bash
       searches  each  element  of the PATH for a directory containing an executable file by that
       name.  Bash uses a hash table to remember the full pathnames of executable files (see hash
       under  SHELL  BUILTIN  COMMANDS  below).   A  full  search  of  the directories in PATH is
       performed only if the command  is  not  found  in  the  hash  table.   If  the  search  is
       unsuccessful,    the    shell    searches    for    a   defined   shell   function   named
       command_not_found_handle.  If that function exists, it is invoked in a separate  execution
       environment  with  the  original  command  and  the  original  command's  arguments as its
       arguments, and the function's exit status becomes the exit status of  that  subshell.   If
       that function is not defined, the shell prints an error message and returns an exit status
       of 127.

       If the search is successful, or if the command name contains  one  or  more  slashes,  the
       shell  executes  the named program in a separate execution environment.  Argument 0 is set
       to the name given, and the remaining arguments to the command are  set  to  the  arguments
       given, if any.

       If  this execution fails because the file is not in executable format, and the file is not
       a directory, it is assumed to be a shell script, a file containing shell commands, and the
       shell creates a new instance of itself to execute it.  This subshell reinitializes itself,
       so that the effect is as if a new shell had been invoked to handle the  script,  with  the
       exception  that  the  locations of commands remembered by the parent (see hash below under
       SHELL BUILTIN COMMANDS) are retained by the child.

       If the program is a file beginning with #!, the remainder of the first line  specifies  an
       interpreter  for  the  program.  The shell executes the specified interpreter on operating
       systems that do not handle this  executable  format  themselves.   The  arguments  to  the
       interpreter  consist  of  a single optional argument following the interpreter name on the
       first line of the program, followed by the name of the program, followed  by  the  command
       arguments, if any.

COMMAND EXECUTION ENVIRONMENT

       The shell has an execution environment, which consists of the following:

       •      open  files  inherited  by  the  shell  at  invocation, as modified by redirections
              supplied to the exec builtin

       •      the current working directory as set by cd, pushd, or popd,  or  inherited  by  the
              shell at invocation

       •      the file creation mode mask as set by umask or inherited from the shell's parent

       •      current traps set by trap

       •      shell  parameters that are set by variable assignment or with set or inherited from
              the shell's parent in the environment

       •      shell functions defined during execution or inherited from the  shell's  parent  in
              the environment

       •      options enabled at invocation (either by default or with command-line arguments) or
              by set

       •      options enabled by shopt

       •      shell aliases defined with alias

       •      various process IDs, including those of background jobs, the value of $$,  and  the
              value of PPID

       When  a  simple  command  other  than a builtin or shell function is to be executed, it is
       invoked in a separate execution  environment  that  consists  of  the  following.   Unless
       otherwise noted, the values are inherited from the shell.

       •      the  shell's  open  files,  plus  any  modifications  and  additions  specified  by
              redirections to the command

       •      the current working directory

       •      the file creation mode mask

       •      shell variables and functions marked for export, along with variables exported  for
              the command, passed in the environment

       •      traps  caught  by  the  shell  are  reset  to the values inherited from the shell's
              parent, and traps ignored by the shell are ignored

       A command invoked in  this  separate  environment  cannot  affect  the  shell's  execution
       environment.

       A subshell is a copy of the shell process.

       Command  substitution,  commands  grouped  with parentheses, and asynchronous commands are
       invoked in a subshell environment that is a duplicate of  the  shell  environment,  except
       that  traps  caught by the shell are reset to the values that the shell inherited from its
       parent at invocation.  Builtin commands that are invoked as part of a  pipeline  are  also
       executed  in  a  subshell  environment.   Changes  made to the subshell environment cannot
       affect the shell's execution environment.

       Subshells spawned to execute command substitutions inherit the value of the -e option from
       the parent shell.  When not in posix mode, bash clears the -e option in such subshells.

       If  a command is followed by a & and job control is not active, the default standard input
       for the command is the empty file /dev/null.  Otherwise, the invoked command inherits  the
       file descriptors of the calling shell as modified by redirections.

ENVIRONMENT

       When a program is invoked it is given an array of strings called the environment.  This is
       a list of name-value pairs, of the form name=value.

       The shell provides several ways to manipulate the environment.  On invocation,  the  shell
       scans  its  own  environment  and  creates  a parameter for each name found, automatically
       marking it for export to child processes.  Executed commands inherit the environment.  The
       export  and  declare -x commands allow parameters and functions to be added to and deleted
       from the environment.  If the value of a parameter in the environment is modified, the new
       value  becomes  part  of the environment, replacing the old.  The environment inherited by
       any executed command consists of the shell's initial  environment,  whose  values  may  be
       modified in the shell, less any pairs removed by the unset command, plus any additions via
       the export and declare -x commands.

       The environment for any simple  command  or  function  may  be  augmented  temporarily  by
       prefixing  it  with  parameter  assignments,  as  described  above  in  PARAMETERS.  These
       assignment statements affect only the environment seen by that command.

       If the -k option  is  set  (see  the  set  builtin  command  below),  then  all  parameter
       assignments  are  placed in the environment for a command, not just those that precede the
       command name.

       When bash invokes an external command, the variable _ is set to the full filename  of  the
       command and passed to that command in its environment.

EXIT STATUS

       The exit status of an executed command is the value returned by the waitpid system call or
       equivalent function.  Exit statuses fall between 0 and 255, though,  as  explained  below,
       the  shell  may  use  values  above  125 specially.  Exit statuses from shell builtins and
       compound commands are also limited to this range.  Under certain circumstances, the  shell
       will use special values to indicate specific failure modes.

       For the shell's purposes, a command which exits with a zero exit status has succeeded.  An
       exit status of zero indicates success.  A non-zero exit status indicates failure.  When  a
       command terminates on a fatal signal N, bash uses the value of 128+N as the exit status.

       If  a  command  is  not found, the child process created to execute it returns a status of
       127.  If a command is found but is not executable, the return status is 126.

       If a command fails because of an error during expansion or redirection, the exit status is
       greater than zero.

       Shell  builtin commands return a status of 0 (true) if successful, and non-zero (false) if
       an error occurs while they execute.  All builtins return an exit status of 2  to  indicate
       incorrect usage, generally invalid options or missing arguments.

       The exit status of the last command is available in the special parameter $?.

       Bash  itself  returns  the exit status of the last command executed, unless a syntax error
       occurs, in which case it exits with a non-zero value.  See also the exit  builtin  command
       below.

SIGNALS

       When  bash is interactive, in the absence of any traps, it ignores SIGTERM (so that kill 0
       does not kill an interactive shell), and SIGINT is caught and handled (so  that  the  wait
       builtin  is  interruptible).   In  all  cases, bash ignores SIGQUIT.  If job control is in
       effect, bash ignores SIGTTIN, SIGTTOU, and SIGTSTP.

       Non-builtin commands run by bash have signal handlers set to the values inherited  by  the
       shell  from  its  parent.  When job control is not in effect, asynchronous commands ignore
       SIGINT and SIGQUIT in addition to these inherited handlers.  Commands run as a  result  of
       command  substitution  ignore the keyboard-generated job control signals SIGTTIN, SIGTTOU,
       and SIGTSTP.

       The shell exits by default upon receipt of a SIGHUP.  Before exiting, an interactive shell
       resends  the  SIGHUP  to  all  jobs, running or stopped.  Stopped jobs are sent SIGCONT to
       ensure that they receive the SIGHUP.  To prevent the shell from sending the  signal  to  a
       particular  job,  it  should  be  removed from the jobs table with the disown builtin (see
       SHELL BUILTIN COMMANDS below) or marked to not receive SIGHUP using disown -h.

       If the huponexit shell option has been set with shopt, bash sends a  SIGHUP  to  all  jobs
       when an interactive login shell exits.

       If  bash  is  waiting for a command to complete and receives a signal for which a trap has
       been set, the trap will not be executed until the command completes.  When bash is waiting
       for  an  asynchronous  command via the wait builtin, the reception of a signal for which a
       trap has been set will cause the wait builtin to return immediately with  an  exit  status
       greater than 128, immediately after which the trap is executed.

       When job control is not enabled, and bash is waiting for a foreground command to complete,
       the shell receives keyboard-generated signals such as SIGINT  (usually  generated  by  ^C)
       that  users  commonly  intend to send to that command.  This happens because the shell and
       the command are in the same process group as the terminal, and  ^C  sends  SIGINT  to  all
       processes in that process group.

       When  bash  is running without job control enabled and receives SIGINT while waiting for a
       foreground command, it waits until that foreground command  terminates  and  then  decides
       what to do about the SIGINT:

       1.     If  the command terminates due to the SIGINT, bash concludes that the user meant to
              end the entire script, and acts on the SIGINT (e.g., by running a  SIGINT  trap  or
              exiting itself);

       2.     If  the  command  does  not terminate due to SIGINT, the program handled the SIGINT
              itself and did not treat it as a fatal signal.  In that case, bash does  not  treat
              SIGINT as a fatal signal, either, instead assuming that the SIGINT was used as part
              of the program's normal operation (e.g., emacs uses it to abort  editing  commands)
              or  deliberately  discarded.   However, bash will run any trap set on SIGINT, as it
              does with any other trapped  signal  it  receives  while  it  is  waiting  for  the
              foreground command to complete, for compatibility.

JOB CONTROL

       Job control refers to the ability to selectively stop (suspend) the execution of processes
       and continue (resume) their execution at a later point.  A  user  typically  employs  this
       facility  via  an  interactive interface supplied jointly by the operating system kernel's
       terminal driver and bash.

       The shell associates a job with each pipeline.  It keeps a table  of  currently  executing
       jobs,  which  may  be listed with the jobs command.  When bash starts a job asynchronously
       (in the background), it prints a line that looks like:

              [1] 25647

       indicating that this job is job number 1 and that the process ID of the  last  process  in
       the pipeline associated with this job is 25647.  All of the processes in a single pipeline
       are members of the same job.  Bash uses the job abstraction as the basis for job control.

       To facilitate the implementation of the user  interface  to  job  control,  the  operating
       system  maintains  the  notion  of  a  current terminal process group ID.  Members of this
       process group (processes whose process group ID is equal to the current  terminal  process
       group  ID) receive keyboard-generated signals such as SIGINT.  These processes are said to
       be in the foreground.  Background processes are those whose process group ID differs  from
       the  terminal's; such processes are immune to keyboard-generated signals.  Only foreground
       processes are allowed to read from or, if the user so specifies with stty tostop, write to
       the  terminal.  Background processes which attempt to read from (write to when stty tostop
       is in effect) the terminal are sent a SIGTTIN (SIGTTOU) signal by  the  kernel's  terminal
       driver, which, unless caught, suspends the process.

       If  the  operating  system  on  which  bash is running supports job control, bash contains
       facilities to use it.  Typing the suspend character  (typically  ^Z,  Control-Z)  while  a
       process  is running causes that process to be stopped and returns control to bash.  Typing
       the delayed suspend character (typically ^Y, Control-Y) causes the process to  be  stopped
       when it attempts to read input from the terminal, and control to be returned to bash.  The
       user may then manipulate the state of this job, using the bg command to continue it in the
       background,  the  fg command to continue it in the foreground, or the kill command to kill
       it.  A ^Z takes effect immediately, and has the additional side effect of causing  pending
       output and typeahead to be discarded.

       There  are  a number of ways to refer to a job in the shell.  The character % introduces a
       job specification (jobspec).  Job number n may be referred to as %n.  A job  may  also  be
       referred to using a prefix of the name used to start it, or using a substring that appears
       in its command line.  For example, %ce refers to a stopped job whose command  name  begins
       with  ce.   If  a prefix matches more than one job, bash reports an error.  Using %?ce, on
       the other hand, refers to any job containing the string ce in its command  line.   If  the
       substring  matches  more than one job, bash reports an error.  The symbols %% and %+ refer
       to the shell's notion of the current job, which is the last job stopped while  it  was  in
       the foreground or started in the background.  The previous job may be referenced using %-.
       If there is only a single job, %+ and %- can both be used to refer to that job.  In output
       pertaining  to  jobs  (e.g.,  the  output  of the jobs command), the current job is always
       flagged with a +, and the previous job with a -.  A single %  (with  no  accompanying  job
       specification) also refers to the current job.

       Simply  naming a job can be used to bring it into the foreground: %1 is a synonym for ``fg
       %1'', bringing job 1 from the background into the foreground.  Similarly, ``%1 &'' resumes
       job 1 in the background, equivalent to ``bg %1''.

       The  shell learns immediately whenever a job changes state.  Normally, bash waits until it
       is about to print a prompt before reporting changes  in  a  job's  status  so  as  to  not
       interrupt  any other output.  If the -b option to the set builtin command is enabled, bash
       reports such changes immediately.  Any trap on SIGCHLD is executed  for  each  child  that
       exits.

       If  an  attempt  to  exit  bash is made while jobs are stopped (or, if the checkjobs shell
       option has been enabled using the shopt builtin, running),  the  shell  prints  a  warning
       message,  and, if the checkjobs option is enabled, lists the jobs and their statuses.  The
       jobs command may then be used to inspect their status.  If a second  attempt  to  exit  is
       made  without  an  intervening  command, the shell does not print another warning, and any
       stopped jobs are terminated.

       When the shell is waiting for a job or process using the wait builtin, and job control  is
       enabled,  wait  will  return when the job changes state. The -f option causes wait to wait
       until the job or process terminates before returning.

PROMPTING

       When executing interactively, bash displays the primary prompt PS1 when  it  is  ready  to
       read  a  command,  and  the  secondary  prompt  PS2 when it needs more input to complete a
       command.  Bash displays PS0 after it reads  a  command  but  before  executing  it.   Bash
       displays PS4 as described above before tracing each command when the -x option is enabled.
       Bash allows these prompt strings to be customized by  inserting  a  number  of  backslash-
       escaped special characters that are decoded as follows:
              \a     an ASCII bell character (07)
              \d     the date in "Weekday Month Date" format (e.g., "Tue May 26")
              \D{format}
                     the  format  is  passed  to  strftime(3) and the result is inserted into the
                     prompt  string;  an  empty  format  results  in   a   locale-specific   time
                     representation.  The braces are required
              \e     an ASCII escape character (033)
              \h     the hostname up to the first `.'
              \H     the hostname
              \j     the number of jobs currently managed by the shell
              \l     the basename of the shell's terminal device name
              \n     newline
              \r     carriage return
              \s     the  name  of the shell, the basename of $0 (the portion following the final
                     slash)
              \t     the current time in 24-hour HH:MM:SS format
              \T     the current time in 12-hour HH:MM:SS format
              \@     the current time in 12-hour am/pm format
              \A     the current time in 24-hour HH:MM format
              \u     the username of the current user
              \v     the version of bash (e.g., 2.00)
              \V     the release of bash, version + patch level (e.g., 2.00.0)
              \w     the value of the PWD shell variable ($PWD), with $HOME  abbreviated  with  a
                     tilde (uses the value of the PROMPT_DIRTRIM variable)
              \W     the basename of $PWD, with $HOME abbreviated with a tilde
              \!     the history number of this command
              \#     the command number of this command
              \$     if the effective UID is 0, a #, otherwise a $
              \nnn   the character corresponding to the octal number nnn
              \\     a backslash
              \[     begin  a sequence of non-printing characters, which could be used to embed a
                     terminal control sequence into the prompt
              \]     end a sequence of non-printing characters

       The command number and the history number are usually different: the history number  of  a
       command  is its position in the history list, which may include commands restored from the
       history file (see HISTORY below), while the command number is the position in the sequence
       of commands executed during the current shell session.  After the string is decoded, it is
       expanded via parameter expansion, command substitution, arithmetic  expansion,  and  quote
       removal,  subject  to the value of the promptvars shell option (see the description of the
       shopt command under SHELL BUILTIN COMMANDS below).  This can have unwanted side effects if
       escaped  portions  of  the string appear within command substitution or contain characters
       special to word expansion.

READLINE

       This is the library that handles reading input when using an interactive shell, unless the
       --noediting option is given at shell invocation.  Line editing is also used when using the
       -e option to the read builtin.  By default, the line editing commands are similar to those
       of  Emacs.   A  vi-style  line  editing  interface is also available.  Line editing can be
       enabled at any time using the -o emacs or -o vi options to  the  set  builtin  (see  SHELL
       BUILTIN  COMMANDS below).  To turn off line editing after the shell is running, use the +o
       emacs or +o vi options to the set builtin.

   Readline Notation
       In this section, the Emacs-style notation is used to denote keystrokes.  Control keys  are
       denoted  by  C-key, e.g., C-n means Control-N.  Similarly, meta keys are denoted by M-key,
       so M-x means Meta-X.  (On keyboards without a meta key, M-x means ESC x, i.e.,  press  the
       Escape  key  then the x key.  This makes ESC the meta prefix.  The combination M-C-x means
       ESC-Control-x, or press the Escape key then hold the Control  key  while  pressing  the  x
       key.)

       Readline  commands  may  be given numeric arguments, which normally act as a repeat count.
       Sometimes, however, it is the sign  of  the  argument  that  is  significant.   Passing  a
       negative argument to a command that acts in the forward direction (e.g., kill-line) causes
       that command to act in a backward  direction.   Commands  whose  behavior  with  arguments
       deviates from this are noted below.

       When a command is described as killing text, the text deleted is saved for possible future
       retrieval (yanking).  The killed text is saved in a kill ring.   Consecutive  kills  cause
       the text to be accumulated into one unit, which can be yanked all at once.  Commands which
       do not kill text separate the chunks of text on the kill ring.

   Readline Initialization
       Readline is customized by putting commands in an initialization file (the  inputrc  file).
       The  name  of this file is taken from the value of the INPUTRC variable.  If that variable
       is unset, the default is ~/.inputrc.  If that file  does not exist or cannot be read,  the
       ultimate  default  is /etc/inputrc.  When a program which uses the readline library starts
       up, the initialization file is read, and the key bindings and variables  are  set.   There
       are  only a few basic constructs allowed in the readline initialization file.  Blank lines
       are ignored.  Lines beginning with a # are comments.  Lines beginning with  a  $  indicate
       conditional constructs.  Other lines denote key bindings and variable settings.

       The  default  key-bindings  may  be changed with an inputrc file.  Other programs that use
       this library may add their own commands and bindings.

       For example, placing

              M-Control-u: universal-argument
       or
              C-Meta-u: universal-argument
       into the inputrc would make M-C-u execute the readline command universal-argument.

       The following symbolic character names are recognized: RUBOUT,  DEL,  ESC,  LFD,  NEWLINE,
       RET, RETURN, SPC, SPACE, and TAB.

       In  addition  to  command  names,  readline  allows  keys  to be bound to a string that is
       inserted when the key is pressed (a macro).

   Readline Key Bindings
       The syntax for controlling key bindings in the  inputrc  file  is  simple.   All  that  is
       required  is the name of the command or the text of a macro and a key sequence to which it
       should be bound.  The name may be specified in one of two ways: as a  symbolic  key  name,
       possibly with Meta- or Control- prefixes, or as a key sequence.

       When  using  the form keyname:function-name or macro, keyname is the name of a key spelled
       out in English.  For example:

              Control-u: universal-argument
              Meta-Rubout: backward-kill-word
              Control-o: "> output"

       In the above example, C-u is bound to the function universal-argument, M-DEL is  bound  to
       the  function backward-kill-word, and C-o is bound to run the macro expressed on the right
       hand side (that is, to insert the text ``> output'' into the line).

       In the second form, "keyseq":function-name or macro, keyseq differs from keyname above  in
       that  strings  denoting  an  entire  key sequence may be specified by placing the sequence
       within double quotes.  Some GNU Emacs style key escapes can be used, as in  the  following
       example, but the symbolic character names are not recognized.

              "\C-u": universal-argument
              "\C-x\C-r": re-read-init-file
              "\e[11~": "Function Key 1"

       In  this example, C-u is again bound to the function universal-argument.  C-x C-r is bound
       to the function re-read-init-file, and ESC [ 1 1 ~ is bound to insert the text  ``Function
       Key 1''.

       The full set of GNU Emacs style escape sequences is
              \C-    control prefix
              \M-    meta prefix
              \e     an escape character
              \\     backslash
              \"     literal "
              \'     literal '

       In  addition to the GNU Emacs style escape sequences, a second set of backslash escapes is
       available:
              \a     alert (bell)
              \b     backspace
              \d     delete
              \f     form feed
              \n     newline
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \nnn   the eight-bit character whose value is the octal value  nnn  (one  to  three
                     digits)
              \xHH   the  eight-bit character whose value is the hexadecimal value HH (one or two
                     hex digits)

       When entering the text of a macro, single or double quotes must  be  used  to  indicate  a
       macro definition.  Unquoted text is assumed to be a function name.  In the macro body, the
       backslash escapes described above are expanded.  Backslash will quote any other  character
       in the macro text, including " and '.

       Bash  allows  the  current readline key bindings to be displayed or modified with the bind
       builtin command.  The editing mode may be switched during interactive use by using the  -o
       option to the set builtin command (see SHELL BUILTIN COMMANDS below).

   Readline Variables
       Readline has variables that can be used to further customize its behavior.  A variable may
       be set in the inputrc file with a statement of the form

              set variable-name value
       or using the bind builtin command (see SHELL BUILTIN COMMANDS below).

       Except where noted, readline variables can take the values On or Off  (without  regard  to
       case).   Unrecognized variable names are ignored.  When a variable value is read, empty or
       null values, "on" (case-insensitive), and "1" are equivalent to On.  All other values  are
       equivalent to Off.  The variables and their default values are:

       active-region-start-color
              A  string  variable that controls the text color and background when displaying the
              text in the active region (see  the  description  of  enable-active-region  below).
              This string must not take up any physical character positions on the display, so it
              should consist only of terminal escape sequences.  It is  output  to  the  terminal
              before  displaying  the  text  in the active region.  This variable is reset to the
              default value whenever the terminal type changes.  The default value is the  string
              that  puts  the terminal in standout mode, as obtained from the terminal's terminfo
              description.  A sample value might be "\e[01;33m".
       active-region-end-color
              A string variable  that  "undoes"  the  effects  of  active-region-start-color  and
              restores  "normal"  terminal display appearance after displaying text in the active
              region.  This string must not take up  any  physical  character  positions  on  the
              display,  so  it should consist only of terminal escape sequences.  It is output to
              the terminal after displaying the text in the  active  region.   This  variable  is
              reset  to  the default value whenever the terminal type changes.  The default value
              is the string that restores the terminal from standout mode, as obtained  from  the
              terminal's terminfo description.  A sample value might be "\e[0m".
       bell-style (audible)
              Controls  what  happens  when  readline wants to ring the terminal bell.  If set to
              none, readline never rings the bell.  If set to visible, readline  uses  a  visible
              bell  if  one  is  available.   If  set  to  audible, readline attempts to ring the
              terminal's bell.
       bind-tty-special-chars (On)
              If set to On, readline attempts to bind the control characters treated specially by
              the kernel's terminal driver to their readline equivalents.
       blink-matching-paren (Off)
              If  set  to  On,  readline  attempts  to  briefly  move  the  cursor  to an opening
              parenthesis when a closing parenthesis is inserted.
       colored-completion-prefix (Off)
              If set to On, when listing completions, readline displays the common prefix of  the
              set  of  possible  completions  using a different color.  The color definitions are
              taken from the value of the LS_COLORS environment variable.  If there  is  a  color
              definition  in  $LS_COLORS  for  the  custom  suffix  "readline-colored-completion-
              prefix", readline uses this color for the common prefix instead of its default.
       colored-stats (Off)
              If set to On, readline displays possible  completions  using  different  colors  to
              indicate  their  file  type.  The color definitions are taken from the value of the
              LS_COLORS environment variable.
       comment-begin (``#'')
              The string that is inserted when the readline insert-comment command  is  executed.
              This command is bound to M-# in emacs mode and to # in vi command mode.
       completion-display-width (-1)
              The  number  of  screen  columns  used  to display possible matches when performing
              completion.  The value is ignored if it is less than 0 or greater than the terminal
              screen  width.   A value of 0 will cause matches to be displayed one per line.  The
              default value is -1.
       completion-ignore-case (Off)
              If  set  to  On,  readline  performs  filename  matching  and   completion   in   a
              case-insensitive fashion.
       completion-map-case (Off)
              If  set  to  On, and completion-ignore-case is enabled, readline treats hyphens (-)
              and  underscores  (_)  as  equivalent  when  performing  case-insensitive  filename
              matching and completion.
       completion-prefix-display-length (0)
              The  length  in  characters  of the common prefix of a list of possible completions
              that is displayed without modification.  When set to a  value  greater  than  zero,
              common  prefixes  longer  than  this  value  are  replaced  with  an  ellipsis when
              displaying possible completions.
       completion-query-items (100)
              This determines when the user is queried  about  viewing  the  number  of  possible
              completions  generated  by  the possible-completions command.  It may be set to any
              integer value greater than or equal to zero.  If the number of possible completions
              is  greater  than or equal to the value of this variable, readline will ask whether
              or not the user wishes to view them;  otherwise  they  are  simply  listed  on  the
              terminal.   A  zero  value  means  readline  should  never ask; negative values are
              treated as zero.
       convert-meta (On)
              If set to On, readline will convert characters with the eighth bit set to an  ASCII
              key  sequence  by  stripping  the  eighth bit and prefixing an escape character (in
              effect, using escape as the meta prefix).  The default is On, but readline will set
              it  to Off if the locale contains eight-bit characters.  This variable is dependent
              on the LC_CTYPE locale category, and may change if the locale is changed.
       disable-completion (Off)
              If set to On, readline will inhibit word completion.  Completion characters will be
              inserted into the line as if they had been mapped to self-insert.
       echo-control-characters (On)
              When set to On, on operating systems that indicate they support it, readline echoes
              a character corresponding to a signal generated from the keyboard.
       editing-mode (emacs)
              Controls whether readline begins with a set of key bindings similar to Emacs or vi.
              editing-mode can be set to either emacs or vi.
       emacs-mode-string (@)
              If   the   show-mode-in-prompt  variable  is  enabled,  this  string  is  displayed
              immediately before the last line of the primary prompt when emacs editing  mode  is
              active.  The value is expanded like a key binding, so the standard set of meta- and
              control prefixes and backslash escape sequences is available.  Use the  \1  and  \2
              escapes to begin and end sequences of non-printing characters, which can be used to
              embed a terminal control sequence into the mode string.
       enable-active-region (On)
              The point is the current cursor  position,  and  mark  refers  to  a  saved  cursor
              position.   The text between the point and mark is referred to as the region.  When
              this variable is set to On, readline  allows  certain  commands  to  designate  the
              region  as  active.  When the region is active, readline highlights the text in the
              region using the value of the  active-region-start-color,  which  defaults  to  the
              string that enables the terminal's standout mode.  The active region shows the text
              inserted by bracketed-paste and any matching text found  by  incremental  and  non-
              incremental history searches.
       enable-bracketed-paste (On)
              When  set  to  On,  readline  configures the terminal to insert each paste into the
              editing buffer as a single string of characters, instead of treating each character
              as  if  it  had been read from the keyboard.  This prevents readline from executing
              any editing commands bound to key sequences appearing in the pasted text.
       enable-keypad (Off)
              When set to On, readline will try to enable  the  application  keypad  when  it  is
              called.  Some systems need this to enable the arrow keys.
       enable-meta-key (On)
              When  set  to  On,  readline  will try to enable any meta modifier key the terminal
              claims to support when it is called.  On many terminals, the meta key  is  used  to
              send eight-bit characters.
       expand-tilde (Off)
              If set to On, tilde expansion is performed when readline attempts word completion.
       history-preserve-point (Off)
              If set to On, the history code attempts to place point at the same location on each
              history line retrieved with previous-history or next-history.
       history-size (unset)
              Set the maximum number of history entries saved in the history  list.   If  set  to
              zero,  any  existing  history entries are deleted and no new entries are saved.  If
              set to a value less than zero, the number of history entries is  not  limited.   By
              default,  the  number  of history entries is set to the value of the HISTSIZE shell
              variable.  If an attempt is made to set history-size to a  non-numeric  value,  the
              maximum number of history entries will be set to 500.
       horizontal-scroll-mode (Off)
              When  set  to On, makes readline use a single line for display, scrolling the input
              horizontally on a single screen line when it becomes longer than the  screen  width
              rather  than  wrapping  to  a  new line.  This setting is automatically enabled for
              terminals of height 1.
       input-meta (Off)
              If set to On, readline will enable eight-bit input (that is, it will not strip  the
              eighth bit from the characters it reads), regardless of what the terminal claims it
              can support.  The name meta-flag is a synonym for this variable.   The  default  is
              Off,  but  readline  will set it to On if the locale contains eight-bit characters.
              This variable is dependent on the LC_CTYPE locale category, and may change  if  the
              locale is changed.
       isearch-terminators (``C-[C-J'')
              The  string  of  characters  that  should  terminate  an incremental search without
              subsequently executing the character as a command.  If this variable has  not  been
              given a value, the characters ESC and C-J will terminate an incremental search.
       keymap (emacs)
              Set  the  current  readline  keymap.   The  set  of  valid  keymap  names is emacs,
              emacs-standard, emacs-meta, emacs-ctlx,  vi,  vi-command,  and  vi-insert.   vi  is
              equivalent to vi-command; emacs is equivalent to emacs-standard.  The default value
              is emacs; the value of editing-mode also affects the default keymap.
       keyseq-timeout (500)
              Specifies the duration readline will wait for a character when reading an ambiguous
              key  sequence  (one  that  can form a complete key sequence using the input read so
              far, or can take additional input to complete a longer key sequence).  If no  input
              is  received  within  the  timeout,  readline will use the shorter but complete key
              sequence.  The value is specified in milliseconds, so a value of  1000  means  that
              readline  will  wait one second for additional input.  If this variable is set to a
              value less than or equal to zero, or to a non-numeric  value,  readline  will  wait
              until another key is pressed to decide which key sequence to complete.
       mark-directories (On)
              If set to On, completed directory names have a slash appended.
       mark-modified-lines (Off)
              If  set to On, history lines that have been modified are displayed with a preceding
              asterisk (*).
       mark-symlinked-directories (Off)
              If set to On, completed names which are symbolic links to directories have a  slash
              appended (subject to the value of mark-directories).
       match-hidden-files (On)
              This  variable,  when  set  to On, causes readline to match files whose names begin
              with a `.' (hidden files) when performing filename completion.  If set to Off,  the
              leading `.' must be supplied by the user in the filename to be completed.
       menu-complete-display-prefix (Off)
              If  set  to  On, menu completion displays the common prefix of the list of possible
              completions (which may be empty) before cycling through the list.
       output-meta (Off)
              If set to On, readline will display characters with the  eighth  bit  set  directly
              rather  than  as a meta-prefixed escape sequence.  The default is Off, but readline
              will set it to On if the locale contains eight-bit characters.   This  variable  is
              dependent on the LC_CTYPE locale category, and may change if the locale is changed.
       page-completions (On)
              If  set  to On, readline uses an internal more-like pager to display a screenful of
              possible completions at a time.
       print-completions-horizontally (Off)
              If set to On, readline will display completions with matches sorted horizontally in
              alphabetical order, rather than down the screen.
       revert-all-at-newline (Off)
              If set to On, readline will undo all changes to history lines before returning when
              accept-line is executed.  By default, history lines  may  be  modified  and  retain
              individual undo lists across calls to readline.
       show-all-if-ambiguous (Off)
              This  alters the default behavior of the completion functions.  If set to On, words
              which have more than one  possible  completion  cause  the  matches  to  be  listed
              immediately instead of ringing the bell.
       show-all-if-unmodified (Off)
              This  alters  the default behavior of the completion functions in a fashion similar
              to show-all-if-ambiguous.  If set to On, words which have more  than  one  possible
              completion  without any possible partial completion (the possible completions don't
              share a common prefix) cause the  matches  to  be  listed  immediately  instead  of
              ringing the bell.
       show-mode-in-prompt (Off)
              If  set  to  On, add a string to the beginning of the prompt indicating the editing
              mode: emacs, vi command, or vi  insertion.   The  mode  strings  are  user-settable
              (e.g., emacs-mode-string).
       skip-completed-text (Off)
              If  set  to On, this alters the default completion behavior when inserting a single
              match into the line.  It's only active when performing completion in the middle  of
              a  word.   If enabled, readline does not insert characters from the completion that
              match characters after point in the word being completed, so portions of  the  word
              following the cursor are not duplicated.
       vi-cmd-mode-string ((cmd))
              If   the   show-mode-in-prompt  variable  is  enabled,  this  string  is  displayed
              immediately before the last line of the primary prompt  when  vi  editing  mode  is
              active  and  in  command  mode.   The  value is expanded like a key binding, so the
              standard set of meta- and  control  prefixes  and  backslash  escape  sequences  is
              available.   Use  the  \1 and \2 escapes to begin and end sequences of non-printing
              characters, which can be used to embed a terminal control sequence  into  the  mode
              string.
       vi-ins-mode-string ((ins))
              If   the   show-mode-in-prompt  variable  is  enabled,  this  string  is  displayed
              immediately before the last line of the primary prompt  when  vi  editing  mode  is
              active  and  in  insertion  mode.  The value is expanded like a key binding, so the
              standard set of meta- and  control  prefixes  and  backslash  escape  sequences  is
              available.   Use  the  \1 and \2 escapes to begin and end sequences of non-printing
              characters, which can be used to embed a terminal control sequence  into  the  mode
              string.
       visible-stats (Off)
              If set to On, a character denoting a file's type as reported by stat(2) is appended
              to the filename when listing possible completions.

   Readline Conditional Constructs
       Readline implements a facility similar in spirit to the conditional  compilation  features
       of  the  C preprocessor which allows key bindings and variable settings to be performed as
       the result of tests.  There are four parser directives used.

       $if    The $if construct allows bindings to  be  made  based  on  the  editing  mode,  the
              terminal  being  used,  or  the  application using readline.  The text of the test,
              after any comparison operator,
               extends to the end of the line; unless otherwise noted, no characters are required
              to isolate it.

              mode   The  mode=  form of the $if directive is used to test whether readline is in
                     emacs or vi mode.  This may be used  in  conjunction  with  the  set  keymap
                     command,  for instance, to set bindings in the emacs-standard and emacs-ctlx
                     keymaps only if readline is starting out in emacs mode.

              term   The term= form may  be  used  to  include  terminal-specific  key  bindings,
                     perhaps  to  bind  the key sequences output by the terminal's function keys.
                     The word on the right side of the = is tested against both the full name  of
                     the  terminal and the portion of the terminal name before the first -.  This
                     allows sun to match both sun and sun-cmd, for instance.

              version
                     The version test  may  be  used  to  perform  comparisons  against  specific
                     readline  versions.   The  version  expands to the current readline version.
                     The set of comparison operators includes =, (and ==), !=, <=, >=, <, and  >.
                     The  version number supplied on the right side of the operator consists of a
                     major version number, an optional  decimal  point,  and  an  optional  minor
                     version (e.g., 7.1). If the minor version is omitted, it is assumed to be 0.
                     The operator may be separated from the string version and from  the  version
                     number argument by whitespace.

              application
                     The  application construct is used to include application-specific settings.
                     Each program using the readline library sets the application  name,  and  an
                     initialization  file can test for a particular value.  This could be used to
                     bind key  sequences  to  functions  useful  for  a  specific  program.   For
                     instance,  the following command adds a key sequence that quotes the current
                     or previous word in bash:

                     $if Bash
                     # Quote the current or previous word
                     "\C-xq": "\eb\"\ef\""
                     $endif

              variable
                     The variable construct provides simple equality tests for readline variables
                     and  values.   The  permitted  comparison  operators are =, ==, and !=.  The
                     variable name must be separated from the comparison operator by  whitespace;
                     the  operator  may  be  separated  from  the value on the right hand side by
                     whitespace.  Both string  and  boolean  variables  may  be  tested.  Boolean
                     variables must be tested against the values on and off.

       $endif This command, as seen in the previous example, terminates an $if command.

       $else  Commands in this branch of the $if directive are executed if the test fails.

       $include
              This  directive  takes  a  single  filename  as  an argument and reads commands and
              bindings  from  that  file.   For  example,  the  following  directive  would  read
              /etc/inputrc:

              $include  /etc/inputrc

   Searching
       Readline  provides  commands for searching through the command history (see HISTORY below)
       for lines containing a specified string.  There are two search modes: incremental and non-
       incremental.

       Incremental searches begin before the user has finished typing the search string.  As each
       character of the search string is typed, readline displays the next entry from the history
       matching  the string typed so far.  An incremental search requires only as many characters
       as needed to find the desired history entry.  The characters present in the value  of  the
       isearch-terminators  variable  are  used  to  terminate  an  incremental  search.  If that
       variable has not been assigned a value the Escape and Control-J characters will  terminate
       an  incremental  search.   Control-G  will  abort  an  incremental  search and restore the
       original line.  When the search is terminated, the history  entry  containing  the  search
       string becomes the current line.

       To  find  other  matching  entries  in  the  history  list, type Control-S or Control-R as
       appropriate.  This will search backward or forward in  the  history  for  the  next  entry
       matching  the  search  string  typed  so  far.  Any other key sequence bound to a readline
       command will terminate the search and execute that command.  For instance, a newline  will
       terminate  the  search and accept the line, thereby executing the command from the history
       list.

       Readline remembers the last incremental  search  string.   If  two  Control-Rs  are  typed
       without  any  intervening  characters  defining a new search string, any remembered search
       string is used.

       Non-incremental searches read the entire search  string  before  starting  to  search  for
       matching  history  lines.   The  search  string may be typed by the user or be part of the
       contents of the current line.

   Readline Command Names
       The following is a list of the names of the commands and  the  default  key  sequences  to
       which  they  are bound.  Command names without an accompanying key sequence are unbound by
       default.  In the following descriptions, point refers to the current cursor position,  and
       mark  refers  to  a  cursor  position saved by the set-mark command.  The text between the
       point and mark is referred to as the region.

   Commands for Moving
       beginning-of-line (C-a)
              Move to the start of the current line.
       end-of-line (C-e)
              Move to the end of the line.
       forward-char (C-f)
              Move forward a character.
       backward-char (C-b)
              Move back a character.
       forward-word (M-f)
              Move forward to the end of the next  word.   Words  are  composed  of  alphanumeric
              characters (letters and digits).
       backward-word (M-b)
              Move  back  to  the  start  of the current or previous word.  Words are composed of
              alphanumeric characters (letters and digits).
       shell-forward-word
              Move forward to the end of the next word.  Words are delimited by non-quoted  shell
              metacharacters.
       shell-backward-word
              Move  back  to  the  start of the current or previous word.  Words are delimited by
              non-quoted shell metacharacters.
       previous-screen-line
              Attempt to move point to the same physical screen column on the  previous  physical
              screen  line.  This  will  not have the desired effect if the current readline line
              does not take up more than one physical line or if point is not  greater  than  the
              length of the prompt plus the screen width.
       next-screen-line
              Attempt  to  move  point  to  the  same physical screen column on the next physical
              screen line. This will not have the desired effect if  the  current  readline  line
              does  not  take  up  more  than  one  physical line or if the length of the current
              readline line is not greater than the length of the prompt plus the screen width.
       clear-display (M-C-l)
              Clear the screen and, if possible, the terminal's scrollback  buffer,  then  redraw
              the current line, leaving the current line at the top of the screen.
       clear-screen (C-l)
              Clear the screen, then redraw the current line, leaving the current line at the top
              of the screen.  With an argument, refresh the current  line  without  clearing  the
              screen.
       redraw-current-line
              Refresh the current line.

   Commands for Manipulating the History
       accept-line (Newline, Return)
              Accept  the line regardless of where the cursor is.  If this line is non-empty, add
              it to the history list according to the state of the HISTCONTROL variable.  If  the
              line  is  a  modified  history  line, then restore the history line to its original
              state.
       previous-history (C-p)
              Fetch the previous command from the history list, moving back in the list.
       next-history (C-n)
              Fetch the next command from the history list, moving forward in the list.
       beginning-of-history (M-<)
              Move to the first line in the history.
       end-of-history (M->)
              Move to the end of the input history, i.e., the line currently being entered.
       operate-and-get-next (C-o)
              Accept the current line for execution and fetch  the  next  line  relative  to  the
              current  line  from  the  history  for  editing.   A numeric argument, if supplied,
              specifies the history entry to use instead of the current line.
       fetch-history
              With a numeric argument, fetch that entry from the history list  and  make  it  the
              current  line.   Without  an  argument, move back to the first entry in the history
              list.
       reverse-search-history (C-r)
              Search backward starting at the current line and moving `up' through the history as
              necessary.  This is an incremental search.
       forward-search-history (C-s)
              Search  forward  starting at the current line and moving `down' through the history
              as necessary.  This is an incremental search.
       non-incremental-reverse-search-history (M-p)
              Search backward through the history starting at  the  current  line  using  a  non-
              incremental search for a string supplied by the user.
       non-incremental-forward-search-history (M-n)
              Search  forward  through  the  history  using a non-incremental search for a string
              supplied by the user.
       history-search-forward
              Search forward through the history for the string of characters between  the  start
              of the current line and the point.  This is a non-incremental search.
       history-search-backward
              Search  backward through the history for the string of characters between the start
              of the current line and the point.  This is a non-incremental search.
       history-substring-search-backward
              Search backward through the history for the string of characters between the  start
              of the current line and the current cursor position (the point).  The search string
              may match anywhere in a history line.  This is a non-incremental search.
       history-substring-search-forward
              Search forward through the history for the string of characters between  the  start
              of  the  current  line  and  the  point.  The search string may match anywhere in a
              history line.  This is a non-incremental search.
       yank-nth-arg (M-C-y)
              Insert the first argument to the previous command (usually the second word  on  the
              previous line) at point.  With an argument n, insert the nth word from the previous
              command (the words in the previous command begin with word 0).  A negative argument
              inserts  the nth word from the end of the previous command.  Once the argument n is
              computed, the argument is extracted as if  the  "!n"  history  expansion  had  been
              specified.
       yank-last-arg (M-., M-_)
              Insert  the  last  argument  to the previous command (the last word of the previous
              history entry).   With  a  numeric  argument,  behave  exactly  like  yank-nth-arg.
              Successive calls to yank-last-arg move back through the history list, inserting the
              last word (or the word specified by the argument to the first call) of each line in
              turn.   Any  numeric  argument  supplied  to  these successive calls determines the
              direction to move through the history.  A negative argument switches the  direction
              through  the  history (back or forward).  The history expansion facilities are used
              to extract the last word, as if the "!$" history expansion had been specified.
       shell-expand-line (M-C-e)
              Expand the line as the shell does.  This performs alias and  history  expansion  as
              well  as  all  of  the  shell  word  expansions.  See HISTORY EXPANSION below for a
              description of history expansion.
       history-expand-line (M-^)
              Perform history expansion on the current line.  See HISTORY EXPANSION below  for  a
              description of history expansion.
       magic-space
              Perform  history  expansion  on  the  current line and insert a space.  See HISTORY
              EXPANSION below for a description of history expansion.
       alias-expand-line
              Perform alias expansion on the current line.  See ALIASES above for  a  description
              of alias expansion.
       history-and-alias-expand-line
              Perform history and alias expansion on the current line.
       insert-last-argument (M-., M-_)
              A synonym for yank-last-arg.
       edit-and-execute-command (C-x C-e)
              Invoke  an  editor  on  the  current  command line, and execute the result as shell
              commands.  Bash attempts to invoke $VISUAL, $EDITOR, and emacs as  the  editor,  in
              that order.

   Commands for Changing Text
       end-of-file (usually C-d)
              The  character  indicating  end-of-file  as set, for example, by ``stty''.  If this
              character is read when there are no characters on the line, and  point  is  at  the
              beginning of the line, readline interprets it as the end of input and returns EOF.
       delete-char (C-d)
              Delete  the character at point.  If this function is bound to the same character as
              the tty EOF character, as C-d commonly is, see above for the effects.
       backward-delete-char (Rubout)
              Delete the character behind the cursor.  When given a numeric  argument,  save  the
              deleted text on the kill ring.
       forward-backward-delete-char
              Delete the character under the cursor, unless the cursor is at the end of the line,
              in which case the character behind the cursor is deleted.
       quoted-insert (C-q, C-v)
              Add the next character  typed  to  the  line  verbatim.   This  is  how  to  insert
              characters like C-q, for example.
       tab-insert (C-v TAB)
              Insert a tab character.
       self-insert (a, b, A, 1, !, ...)
              Insert the character typed.
       transpose-chars (C-t)
              Drag  the  character before point forward over the character at point, moving point
              forward as well.  If point is at the end of the line, then this transposes the  two
              characters before point.  Negative arguments have no effect.
       transpose-words (M-t)
              Drag  the  word before point past the word after point, moving point over that word
              as well.  If point is at the end of the line, this transposes the last two words on
              the line.
       upcase-word (M-u)
              Uppercase the current (or following) word.  With a negative argument, uppercase the
              previous word, but do not move point.
       downcase-word (M-l)
              Lowercase the current (or following) word.  With a negative argument, lowercase the
              previous word, but do not move point.
       capitalize-word (M-c)
              Capitalize  the  current (or following) word.  With a negative argument, capitalize
              the previous word, but do not move point.
       overwrite-mode
              Toggle overwrite mode.  With an explicit positive  numeric  argument,  switches  to
              overwrite mode.  With an explicit non-positive numeric argument, switches to insert
              mode.  This command affects only emacs mode; vi mode  does  overwrite  differently.
              Each call to readline() starts in insert mode.  In overwrite mode, characters bound
              to self-insert replace the text at point rather than pushing the text to the right.
              Characters  bound to backward-delete-char replace the character before point with a
              space.  By default, this command is unbound.

   Killing and Yanking
       kill-line (C-k)
              Kill the text from point to the end of the line.
       backward-kill-line (C-x Rubout)
              Kill backward to the beginning of the line.
       unix-line-discard (C-u)
              Kill backward from point to the beginning of the line.  The killed text is saved on
              the kill-ring.
       kill-whole-line
              Kill all characters on the current line, no matter where point is.
       kill-word (M-d)
              Kill  from point to the end of the current word, or if between words, to the end of
              the next word.  Word boundaries are the same as those used by forward-word.
       backward-kill-word (M-Rubout)
              Kill the word behind point.   Word  boundaries  are  the  same  as  those  used  by
              backward-word.
       shell-kill-word
              Kill  from point to the end of the current word, or if between words, to the end of
              the next word.  Word boundaries are the same as those used by shell-forward-word.
       shell-backward-kill-word
              Kill the word behind point.   Word  boundaries  are  the  same  as  those  used  by
              shell-backward-word.
       unix-word-rubout (C-w)
              Kill  the word behind point, using white space as a word boundary.  The killed text
              is saved on the kill-ring.
       unix-filename-rubout
              Kill the word behind point, using white space and the slash character as  the  word
              boundaries.  The killed text is saved on the kill-ring.
       delete-horizontal-space (M-\)
              Delete all spaces and tabs around point.
       kill-region
              Kill the text in the current region.
       copy-region-as-kill
              Copy the text in the region to the kill buffer.
       copy-backward-word
              Copy the word before point to the kill buffer.  The word boundaries are the same as
              backward-word.
       copy-forward-word
              Copy the word following point to the kill buffer.  The word boundaries are the same
              as forward-word.
       yank (C-y)
              Yank the top of the kill ring into the buffer at point.
       yank-pop (M-y)
              Rotate the kill ring, and yank the new top.  Only works following yank or yank-pop.

   Numeric Arguments
       digit-argument (M-0, M-1, ..., M--)
              Add  this digit to the argument already accumulating, or start a new argument.  M--
              starts a negative argument.
       universal-argument
              This is another way to specify an argument.  If this command is followed by one  or
              more  digits,  optionally  with  a  leading  minus  sign,  those  digits define the
              argument.  If the command is followed by digits, executing universal-argument again
              ends  the  numeric  argument, but is otherwise ignored.  As a special case, if this
              command is immediately followed by a character that is neither a  digit  nor  minus
              sign,  the argument count for the next command is multiplied by four.  The argument
              count is initially one, so  executing  this  function  the  first  time  makes  the
              argument count four, a second time makes the argument count sixteen, and so on.

   Completing
       complete (TAB)
              Attempt  to  perform completion on the text before point.  Bash attempts completion
              treating the text as a variable (if the text begins with $), username (if the  text
              begins with ~), hostname (if the text begins with @), or command (including aliases
              and functions) in turn.  If none of these produces a match, filename completion  is
              attempted.
       possible-completions (M-?)
              List the possible completions of the text before point.
       insert-completions (M-*)
              Insert  all  completions of the text before point that would have been generated by
              possible-completions.
       menu-complete
              Similar to complete, but replaces the word to be completed with a single match from
              the  list  of  possible  completions.   Repeated  execution  of menu-complete steps
              through the list of possible completions, inserting each match in turn.  At the end
              of the list of completions, the bell is rung (subject to the setting of bell-style)
              and the original text is restored.  An argument of n moves n positions  forward  in
              the  list  of matches; a negative argument may be used to move backward through the
              list.  This command is intended to be bound to TAB, but is unbound by default.
       menu-complete-backward
              Identical to menu-complete,  but  moves  backward  through  the  list  of  possible
              completions,  as if menu-complete had been given a negative argument.  This command
              is unbound by default.
       delete-char-or-list
              Deletes the character under the cursor if not at the beginning or end of  the  line
              (like   delete-char).    If  at  the  end  of  the  line,  behaves  identically  to
              possible-completions.  This command is unbound by default.
       complete-filename (M-/)
              Attempt filename completion on the text before point.
       possible-filename-completions (C-x /)
              List the possible completions of the text before point, treating it as a filename.
       complete-username (M-~)
              Attempt completion on the text before point, treating it as a username.
       possible-username-completions (C-x ~)
              List the possible completions of the text before point, treating it as a username.
       complete-variable (M-$)
              Attempt completion on the text before point, treating it as a shell variable.
       possible-variable-completions (C-x $)
              List the possible completions of the text before point,  treating  it  as  a  shell
              variable.
       complete-hostname (M-@)
              Attempt completion on the text before point, treating it as a hostname.
       possible-hostname-completions (C-x @)
              List the possible completions of the text before point, treating it as a hostname.
       complete-command (M-!)
              Attempt  completion  on  the  text  before  point,  treating  it as a command name.
              Command completion attempts to match the  text  against  aliases,  reserved  words,
              shell functions, shell builtins, and finally executable filenames, in that order.
       possible-command-completions (C-x !)
              List  the  possible  completions of the text before point, treating it as a command
              name.
       dynamic-complete-history (M-TAB)
              Attempt completion on the text before point, comparing the text against lines  from
              the history list for possible completion matches.
       dabbrev-expand
              Attempt  menu completion on the text before point, comparing the text against lines
              from the history list for possible completion matches.
       complete-into-braces (M-{)
              Perform filename completion and insert the list of  possible  completions  enclosed
              within braces so the list is available to the shell (see Brace Expansion above).

   Keyboard Macros
       start-kbd-macro (C-x ()
              Begin saving the characters typed into the current keyboard macro.
       end-kbd-macro (C-x ))
              Stop  saving  the  characters  typed  into the current keyboard macro and store the
              definition.
       call-last-kbd-macro (C-x e)
              Re-execute the last keyboard macro defined, by making the characters in  the  macro
              appear as if typed at the keyboard.
       print-last-kbd-macro ()
              Print the last keyboard macro defined in a format suitable for the inputrc file.

   Miscellaneous
       re-read-init-file (C-x C-r)
              Read  in the contents of the inputrc file, and incorporate any bindings or variable
              assignments found there.
       abort (C-g)
              Abort the current editing command and ring the  terminal's  bell  (subject  to  the
              setting of bell-style).
       do-lowercase-version (M-A, M-B, M-x, ...)
              If  the  metafied  character  x  is uppercase, run the command that is bound to the
              corresponding metafied lowercase character.  The behavior  is  undefined  if  x  is
              already lowercase.
       prefix-meta (ESC)
              Metafy the next character typed.  ESC f is equivalent to Meta-f.
       undo (C-_, C-x C-u)
              Incremental undo, separately remembered for each line.
       revert-line (M-r)
              Undo all changes made to this line.  This is like executing the undo command enough
              times to return the line to its initial state.
       tilde-expand (M-&)
              Perform tilde expansion on the current word.
       set-mark (C-@, M-<space>)
              Set the mark to the point.  If a numeric argument is supplied, the mark is  set  to
              that position.
       exchange-point-and-mark (C-x C-x)
              Swap  the  point  with  the  mark.  The current cursor position is set to the saved
              position, and the old cursor position is saved as the mark.
       character-search (C-])
              A character is read and point is moved to the next occurrence of that character.  A
              negative argument searches for previous occurrences.
       character-search-backward (M-C-])
              A  character  is  read  and  point  is  moved  to  the  previous occurrence of that
              character.  A negative argument searches for subsequent occurrences.
       skip-csi-sequence
              Read enough characters to consume a multi-key sequence such as  those  defined  for
              keys  like  Home  and  End.  Such sequences begin with a Control Sequence Indicator
              (CSI), usually ESC-[.  If this sequence is  bound  to  "\[",  keys  producing  such
              sequences  will  have  no  effect  unless  explicitly  bound to a readline command,
              instead of inserting stray characters into the editing buffer.  This is unbound  by
              default, but usually bound to ESC-[.
       insert-comment (M-#)
              Without  a  numeric  argument,  the value of the readline comment-begin variable is
              inserted at the beginning of the current line.  If a numeric argument is  supplied,
              this  command  acts  as a toggle: if the characters at the beginning of the line do
              not match the  value  of  comment-begin,  the  value  is  inserted,  otherwise  the
              characters  in comment-begin are deleted from the beginning of the line.  In either
              case, the line is accepted as if a newline had been typed.  The  default  value  of
              comment-begin  causes  this command to make the current line a shell comment.  If a
              numeric argument causes the comment character to  be  removed,  the  line  will  be
              executed by the shell.
       spell-correct-word (C-x s)
              Perform  spelling  correction  on  the  current word, treating it as a directory or
              filename, in the same way as the cdspell shell option.   Word  boundaries  are  the
              same as those used by shell-forward-word.
       glob-complete-word (M-g)
              The  word  before  point  is  treated  as a pattern for pathname expansion, with an
              asterisk implicitly appended.  This pattern is used to generate a list of  matching
              filenames for possible completions.
       glob-expand-word (C-x *)
              The  word before point is treated as a pattern for pathname expansion, and the list
              of matching filenames is inserted, replacing the word.  If a  numeric  argument  is
              supplied, an asterisk is appended before pathname expansion.
       glob-list-expansions (C-x g)
              The  list  of  expansions  that  would  have  been generated by glob-expand-word is
              displayed, and the line is redrawn.  If a numeric argument is supplied, an asterisk
              is appended before pathname expansion.
       dump-functions
              Print  all  of  the functions and their key bindings to the readline output stream.
              If a numeric argument is supplied, the output is formatted in such a  way  that  it
              can be made part of an inputrc file.
       dump-variables
              Print  all  of  the  settable  readline  variables and their values to the readline
              output stream.  If a numeric argument is supplied, the output is formatted in  such
              a way that it can be made part of an inputrc file.
       dump-macros
              Print  all  of  the  readline  key  sequences  bound to macros and the strings they
              output.  If a numeric argument is supplied, the output is formatted in such  a  way
              that it can be made part of an inputrc file.
       display-shell-version (C-x C-v)
              Display version information about the current instance of bash.

   Programmable Completion
       When  word  completion  is  attempted  for an argument to a command for which a completion
       specification (a compspec) has been defined using the complete builtin (see SHELL  BUILTIN
       COMMANDS below), the programmable completion facilities are invoked.

       First,  the  command  name  is  identified.   If  the  command  word  is  the empty string
       (completion attempted at the beginning of an empty line), any compspec defined with the -E
       option to complete is used.  If a compspec has been defined for that command, the compspec
       is used to generate the list of possible completions for the word.  If the command word is
       a  full  pathname, a compspec for the full pathname is searched for first.  If no compspec
       is found for the full pathname, an attempt is made to find  a  compspec  for  the  portion
       following  the  final  slash.  If those searches do not result in a compspec, any compspec
       defined with the -D option to complete is used as the default.  If  there  is  no  default
       compspec,  bash  attempts  alias  expansion  on  the  command  word as a final resort, and
       attempts to find a compspec for the command word from any successful expansion.

       Once a compspec has been found, it is used to generate the list of matching words.   If  a
       compspec  is not found, the default bash completion as described above under Completing is
       performed.

       First, the actions specified by the compspec are used.  Only matches which are prefixed by
       the  word  being completed are returned.  When the -f or -d option is used for filename or
       directory name completion, the shell variable FIGNORE is used to filter the matches.

       Any completions specified by a pathname expansion pattern to the -G option  are  generated
       next.   The  words  generated by the pattern need not match the word being completed.  The
       GLOBIGNORE shell variable is not used to filter the matches, but the FIGNORE  variable  is
       used.

       Next,  the string specified as the argument to the -W option is considered.  The string is
       first split using the characters in the IFS special variable as delimiters.  Shell quoting
       is  honored.  Each word is then expanded using brace expansion, tilde expansion, parameter
       and variable expansion, command substitution, and arithmetic expansion, as described above
       under  EXPANSION.   The  results  are  split  using  the  rules described above under Word
       Splitting.  The results of  the  expansion  are  prefix-matched  against  the  word  being
       completed, and the matching words become the possible completions.

       After  these matches have been generated, any shell function or command specified with the
       -F and -C options is invoked.  When the command or function  is  invoked,  the  COMP_LINE,
       COMP_POINT, COMP_KEY, and COMP_TYPE variables are assigned values as described above under
       Shell Variables.  If a shell function is being  invoked,  the  COMP_WORDS  and  COMP_CWORD
       variables  are also set.  When the function or command is invoked, the first argument ($1)
       is the name of the command whose arguments are being completed, the second  argument  ($2)
       is  the  word  being completed, and the third argument ($3) is the word preceding the word
       being completed on the current command line.  No filtering of  the  generated  completions
       against  the  word  being  completed  is  performed;  the function or command has complete
       freedom in generating the matches.

       Any function specified with -F is invoked first.  The function may use any  of  the  shell
       facilities,  including  the  compgen builtin described below, to generate the matches.  It
       must put the possible completions in the COMPREPLY array variable, one per array element.

       Next, any command specified with the -C option is invoked in an environment equivalent  to
       command  substitution.   It  should  print  a  list  of  completions, one per line, to the
       standard output.  Backslash may be used to escape a newline, if necessary.

       After all of the possible completions are generated, any  filter  specified  with  the  -X
       option  is applied to the list.  The filter is a pattern as used for pathname expansion; a
       & in the pattern is replaced with the text of the word being completed.  A literal  &  may
       be  escaped  with  a  backslash;  the backslash is removed before attempting a match.  Any
       completion that matches the pattern will be removed from the list.  A  leading  !  negates
       the pattern; in this case any completion not matching the pattern will be removed.  If the
       nocasematch shell option is enabled, the match is performed without regard to the case  of
       alphabetic characters.

       Finally,  any  prefix  and  suffix  specified with the -P and -S options are added to each
       member of the completion list, and the result is returned to the readline completion  code
       as the list of possible completions.

       If  the previously-applied actions do not generate any matches, and the -o dirnames option
       was supplied to complete when the compspec  was  defined,  directory  name  completion  is
       attempted.

       If  the  -o  plusdirs  option  was  supplied  to  complete  when the compspec was defined,
       directory name completion is attempted and any matches are added to  the  results  of  the
       other actions.

       By  default,  if  a compspec is found, whatever it generates is returned to the completion
       code as the full set of possible  completions.   The  default  bash  completions  are  not
       attempted,  and  the  readline  default  of  filename  completion  is disabled.  If the -o
       bashdefault option was supplied to complete  when  the  compspec  was  defined,  the  bash
       default completions are attempted if the compspec generates no matches.  If the -o default
       option was supplied  to  complete  when  the  compspec  was  defined,  readline's  default
       completion  will  be  performed  if  the  compspec  (and,  if  attempted, the default bash
       completions) generate no matches.

       When a compspec indicates that directory name  completion  is  desired,  the  programmable
       completion  functions  force  readline  to  append  a  slash  to completed names which are
       symbolic links to directories, subject to  the  value  of  the  mark-directories  readline
       variable, regardless of the setting of the mark-symlinked-directories readline variable.

       There  is  some  support  for dynamically modifying completions.  This is most useful when
       used in combination with a default completion specified with complete -D.   It's  possible
       for  shell functions executed as completion handlers to indicate that completion should be
       retried by returning an exit status of 124.  If a shell function returns 124, and  changes
       the  compspec associated with the command on which completion is being attempted (supplied
       as the first argument when the function is  executed),  programmable  completion  restarts
       from  the beginning, with an attempt to find a new compspec for that command.  This allows
       a set of completions to be built dynamically as completion is attempted, rather than being
       loaded all at once.

       For  instance,  assuming  that  there  is  a  library  of  compspecs,  each kept in a file
       corresponding to the name of the command, the following default completion function  would
       load completions dynamically:

       _completion_loader()
       {
            . "/etc/bash_completion.d/$1.sh" >/dev/null 2>&1 && return 124
       }
       complete -D -F _completion_loader -o bashdefault -o default

HISTORY

       When the -o history option to the set builtin is enabled, the shell provides access to the
       command history, the list of  commands  previously  typed.   The  value  of  the  HISTSIZE
       variable  is  used  as  the number of commands to save in a history list.  The text of the
       last HISTSIZE commands (default 500) is saved.  The  shell  stores  each  command  in  the
       history  list  prior  to  parameter and variable expansion (see EXPANSION above) but after
       history expansion is performed, subject to the values of the  shell  variables  HISTIGNORE
       and HISTCONTROL.

       On  startup,  the  history  is  initialized  from  the file named by the variable HISTFILE
       (default ~/.bash_history).  The file named by the  value  of  HISTFILE  is  truncated,  if
       necessary,  to  contain  no  more  than  the  number  of  lines  specified by the value of
       HISTFILESIZE.  If HISTFILESIZE is unset, or set to null, a non-numeric value, or a numeric
       value  less  than zero, the history file is not truncated.  When the history file is read,
       lines beginning with the history comment character followed immediately  by  a  digit  are
       interpreted as timestamps for the following history line.  These timestamps are optionally
       displayed depending on the value of  the  HISTTIMEFORMAT  variable.   When  a  shell  with
       history  enabled  exits,  the  last  $HISTSIZE  lines  are copied from the history list to
       $HISTFILE.  If the histappend shell option is enabled (see the description of shopt  under
       SHELL  BUILTIN  COMMANDS below), the lines are appended to the history file, otherwise the
       history file is overwritten.  If HISTFILE is unset, or if the history file is  unwritable,
       the  history is not saved.  If the HISTTIMEFORMAT variable is set, time stamps are written
       to the history file, marked with the history comment character, so they may  be  preserved
       across  shell sessions.  This uses the history comment character to distinguish timestamps
       from other history lines.  After saving the history, the  history  file  is  truncated  to
       contain no more than HISTFILESIZE lines.  If HISTFILESIZE is unset, or set to null, a non-
       numeric value, or a numeric value less than zero, the history file is not truncated.

       The builtin command fc (see SHELL BUILTIN COMMANDS below) may be used to list or edit  and
       re-execute  a  portion of the history list.  The history builtin may be used to display or
       modify the history list and manipulate the history file.  When using command-line editing,
       search  commands  are  available  in  each editing mode that provide access to the history
       list.

       The shell allows control  over  which  commands  are  saved  on  the  history  list.   The
       HISTCONTROL  and  HISTIGNORE variables may be set to cause the shell to save only a subset
       of the commands entered.  The cmdhist shell  option,  if  enabled,  causes  the  shell  to
       attempt  to  save  each  line  of  a  multi-line command in the same history entry, adding
       semicolons where necessary to preserve syntactic correctness.  The  lithist  shell  option
       causes  the  shell  to save the command with embedded newlines instead of semicolons.  See
       the description of the shopt builtin below under SHELL BUILTIN COMMANDS for information on
       setting and unsetting shell options.

HISTORY EXPANSION

       The shell supports a history expansion feature that is similar to the history expansion in
       csh.  This section describes what syntax features are available.  This feature is  enabled
       by  default  for  interactive  shells,  and can be disabled using the +H option to the set
       builtin command (see SHELL BUILTIN COMMANDS below).  Non-interactive shells do not perform
       history expansion by default.

       History  expansions introduce words from the history list into the input stream, making it
       easy to repeat commands, insert the arguments to a previous command into the current input
       line, or fix errors in previous commands quickly.

       History expansion is performed immediately after a complete line is read, before the shell
       breaks it into words, and is performed on each line individually without taking quoting on
       previous  lines  into  account.   It  takes place in two parts.  The first is to determine
       which line from the history list to use during substitution.   The  second  is  to  select
       portions  of  that  line  for  inclusion into the current one.  The line selected from the
       history is the event, and the portions of  that  line  that  are  acted  upon  are  words.
       Various modifiers are available to manipulate the selected words.  The line is broken into
       words in the same fashion as when reading input, so that  several  metacharacter-separated
       words  surrounded by quotes are considered one word.  History expansions are introduced by
       the appearance of the history expansion character, which is ! by default.  Only  backslash
       (\) and single quotes can quote the history expansion character, but the history expansion
       character is also treated as quoted if it immediately precedes the closing double quote in
       a double-quoted string.

       Several  characters  inhibit  history expansion if found immediately following the history
       expansion character, even if it is unquoted: space, tab, newline, carriage return, and  =.
       If the extglob shell option is enabled, ( will also inhibit expansion.

       Several  shell  options settable with the shopt builtin may be used to tailor the behavior
       of history expansion.  If the histverify shell option is enabled (see the  description  of
       the  shopt  builtin  below),  and  readline  is  being used, history substitutions are not
       immediately passed to the shell parser.  Instead, the expanded line is reloaded  into  the
       readline  editing  buffer  for  further  modification.  If readline is being used, and the
       histreedit shell option is enabled, a failed history substitution will  be  reloaded  into
       the  readline editing buffer for correction.  The -p option to the history builtin command
       may be used to see what a history expansion will do before using it.  The -s option to the
       history  builtin  may  be  used  to  add  commands  to the end of the history list without
       actually executing them, so that they are available for subsequent recall.

       The shell allows control of the various characters used by the history expansion mechanism
       (see  the  description  of  histchars  above  under  Shell Variables).  The shell uses the
       history comment character to mark history timestamps when writing the history file.

   Event Designators
       An event designator is a reference to a command line entry in the  history  list.   Unless
       the  reference  is  absolute,  events  are relative to the current position in the history
       list.

       !      Start a history substitution, except when followed by a  blank,  newline,  carriage
              return, = or ( (when the extglob shell option is enabled using the shopt builtin).
       !n     Refer to command line n.
       !-n    Refer to the current command minus n.
       !!     Refer to the previous command.  This is a synonym for `!-1'.
       !string
              Refer to the most recent command preceding the current position in the history list
              starting with string.
       !?string[?]
              Refer to the most recent command preceding the current position in the history list
              containing string.  The trailing ? may be omitted if string is followed immediately
              by a newline.  If string is missing, the string from  the  most  recent  search  is
              used; it is an error if there is no previous search string.
       ^string1^string2^
              Quick  substitution.   Repeat the previous command, replacing string1 with string2.
              Equivalent to ``!!:s^string1^string2^'' (see Modifiers below).
       !#     The entire command line typed so far.

   Word Designators
       Word designators are used to select desired words from the event.  A : separates the event
       specification  from  the word designator.  It may be omitted if the word designator begins
       with a ^, $, *, -, or %.  Words are numbered from the beginning  of  the  line,  with  the
       first  word being denoted by 0 (zero).  Words are inserted into the current line separated
       by single spaces.

       0 (zero)
              The zeroth word.  For the shell, this is the command word.
       n      The nth word.
       ^      The first argument.  That is, word 1.
       $      The last word.  This is usually the last argument, but will expand  to  the  zeroth
              word if there is only one word in the line.
       %      The  first  word matched by the most recent `?string?' search, if the search string
              begins with a character that is part of a word.
       x-y    A range of words; `-y' abbreviates `0-y'.
       *      All of the words but the zeroth.  This is a synonym for `1-$'.  It is not an  error
              to  use  *  if there is just one word in the event; the empty string is returned in
              that case.
       x*     Abbreviates x-$.
       x-     Abbreviates x-$ like x*, but omits the last word.  If x is missing, it defaults  to
              0.

       If  a  word designator is supplied without an event specification, the previous command is
       used as the event.

   Modifiers
       After the optional word designator, there may appear a sequence of  one  or  more  of  the
       following  modifiers,  each  preceded  by a `:'.  These modify, or edit, the word or words
       selected from the history event.

       h      Remove a trailing filename component, leaving only the head.
       t      Remove all leading filename components, leaving the tail.
       r      Remove a trailing suffix of the form .xxx, leaving the basename.
       e      Remove all but the trailing suffix.
       p      Print the new command but do not execute it.
       q      Quote the substituted words, escaping further substitutions.
       x      Quote the substituted words as with q, but break into words at blanks and newlines.
              The q and x modifiers are mutually exclusive; the last one supplied is used.
       s/old/new/
              Substitute  new  for  the first occurrence of old in the event line.  Any character
              may be used as the delimiter in place of /.  The final delimiter is optional if  it
              is  the  last  character of the event line.  The delimiter may be quoted in old and
              new with a single backslash.  If & appears in new, it is replaced by old.  A single
              backslash will quote the &.  If old is null, it is set to the last old substituted,
              or, if no  previous  history  substitutions  took  place,  the  last  string  in  a
              !?string[?]  search.  If new is null, each matching old is deleted.
       &      Repeat the previous substitution.
       g      Cause  changes  to  be  applied  over  the  entire  event  line.   This  is used in
              conjunction with `:s' (e.g., `:gs/old/new/') or  `:&'.   If  used  with  `:s',  any
              delimiter  can  be used in place of /, and the final delimiter is optional if it is
              the last character of the event line.  An a may be used as a synonym for g.
       G      Apply the following `s' or `&' modifier once to each word in the event line.

SHELL BUILTIN COMMANDS

       Unless otherwise noted, each builtin command  documented  in  this  section  as  accepting
       options  preceded  by - accepts -- to signify the end of the options.  The :, true, false,
       and test/[ builtins do not accept options and  do  not  treat  --  specially.   The  exit,
       logout,  return,  break,  continue,  let,  and shift builtins accept and process arguments
       beginning with - without requiring --.  Other builtins that accept arguments but  are  not
       specified as accepting options interpret arguments beginning with - as invalid options and
       require -- to prevent this interpretation.
       : [arguments]
              No effect; the command does nothing beyond expanding arguments and  performing  any
              specified redirections.  The return status is zero.

        .  filename [arguments]
       source filename [arguments]
              Read and execute commands from filename in the current shell environment and return
              the exit status of the last command executed from filename.  If filename  does  not
              contain  a  slash,  filenames  in  PATH  are  used to find the directory containing
              filename, but filename does not need to be executable.  The file  searched  for  in
              PATH  need  not  be  executable.   When  bash is not in posix mode, it searches the
              current directory if no file is found in PATH.  If the  sourcepath  option  to  the
              shopt  builtin  command  is turned off, the PATH is not searched.  If any arguments
              are supplied, they become the positional  parameters  when  filename  is  executed.
              Otherwise  the positional parameters are unchanged.  If the -T option is enabled, .
              inherits any trap on DEBUG; if it is not,  any  DEBUG  trap  string  is  saved  and
              restored  around  the call to ., and . unsets the DEBUG trap while it executes.  If
              -T is not set, and the sourced file changes  the  DEBUG  trap,  the  new  value  is
              retained  when  .  completes.   The return status is the status of the last command
              exited within the script (0 if no commands are executed), and false if filename  is
              not found or cannot be read.

       alias [-p] [name[=value] ...]
              Alias  with  no  arguments  or with the -p option prints the list of aliases in the
              form alias name=value on standard output.  When arguments are supplied, an alias is
              defined  for  each name whose value is given.  A trailing space in value causes the
              next word to be checked for alias substitution when the  alias  is  expanded.   For
              each  name  in the argument list for which no value is supplied, the name and value
              of the alias is printed.  Alias returns true unless a name is given  for  which  no
              alias has been defined.

       bg [jobspec ...]
              Resume each suspended job jobspec in the background, as if it had been started with
              &.  If jobspec is not present, the shell's notion of the current job is  used.   bg
              jobspec  returns  0  unless  run when job control is disabled or, when run with job
              control enabled, any specified jobspec was not found or  was  started  without  job
              control.

       bind [-m keymap] [-lpsvPSVX]
       bind [-m keymap] [-q function] [-u function] [-r keyseq]
       bind [-m keymap] -f filename
       bind [-m keymap] -x keyseq:shell-command
       bind [-m keymap] keyseq:function-name
       bind [-m keymap] keyseq:readline-command
       bind readline-command-line
              Display  current  readline  key  and  function  bindings,  bind a key sequence to a
              readline function or macro, or set a readline variable.  Each  non-option  argument
              is a command as it would appear in a readline initialization file such as .inputrc,
              but each  binding  or  command  must  be  passed  as  a  separate  argument;  e.g.,
              '"\C-x\C-r":   re-read-init-file'.    Options,  if  supplied,  have  the  following
              meanings:
              -m keymap
                     Use keymap as  the  keymap  to  be  affected  by  the  subsequent  bindings.
                     Acceptable  keymap  names are emacs, emacs-standard, emacs-meta, emacs-ctlx,
                     vi, vi-move, vi-command, and vi-insert.   vi  is  equivalent  to  vi-command
                     (vi-move is also a synonym); emacs is equivalent to emacs-standard.
              -l     List the names of all readline functions.
              -p     Display  readline function names and bindings in such a way that they can be
                     re-read.
              -P     List current readline function names and bindings.
              -s     Display readline key sequences bound to macros and the strings  they  output
                     in such a way that they can be re-read.
              -S     Display readline key sequences bound to macros and the strings they output.
              -v     Display  readline  variable  names and values in such a way that they can be
                     re-read.
              -V     List current readline variable names and values.
              -f filename
                     Read key bindings from filename.
              -q function
                     Query about which keys invoke the named function.
              -u function
                     Unbind all keys bound to the named function.
              -r keyseq
                     Remove any current binding for keyseq.
              -x keyseq:shell-command
                     Cause shell-command  to  be  executed  whenever  keyseq  is  entered.   When
                     shell-command  is executed, the shell sets the READLINE_LINE variable to the
                     contents  of  the  readline  line  buffer   and   the   READLINE_POINT   and
                     READLINE_MARK  variables  to the current location of the insertion point and
                     the saved insertion point (the mark), respectively.  The shell  assigns  any
                     numeric  argument  the  user supplied to the READLINE_ARGUMENT variable.  If
                     there was no argument, that variable is not set.  If  the  executed  command
                     changes the value of any of READLINE_LINE, READLINE_POINT, or READLINE_MARK,
                     those new values will be reflected in the editing state.
              -X     List all key sequences bound to shell commands and the  associated  commands
                     in a format that can be reused as input.

              The return value is 0 unless an unrecognized option is given or an error occurred.

       break [n]
              Exit  from  within a for, while, until, or select loop.  If n is specified, break n
              levels.  n must be ≥ 1.  If n is greater than the number of  enclosing  loops,  all
              enclosing  loops are exited.  The return value is 0 unless n is not greater than or
              equal to 1.

       builtin shell-builtin [arguments]
              Execute the specified shell builtin, passing it  arguments,  and  return  its  exit
              status.   This is useful when defining a function whose name is the same as a shell
              builtin, retaining the functionality of the builtin within the  function.   The  cd
              builtin   is   commonly  redefined  this  way.   The  return  status  is  false  if
              shell-builtin is not a shell builtin command.

       caller [expr]
              Returns the context of any active subroutine call (a shell  function  or  a  script
              executed  with  the  . or source builtins).  Without expr, caller displays the line
              number and source filename of the  current  subroutine  call.   If  a  non-negative
              integer  is supplied as expr, caller displays the line number, subroutine name, and
              source file corresponding to that position in the  current  execution  call  stack.
              This  extra  information  may  be  used,  for example, to print a stack trace.  The
              current frame is frame 0.  The return value is 0 unless the shell is not  executing
              a  subroutine  call  or  expr  does  not correspond to a valid position in the call
              stack.

       cd [-L|[-P [-e]] [-@]] [dir]
              Change the current directory to dir.  if dir is not supplied, the value of the HOME
              shell variable is the default.  The variable CDPATH defines the search path for the
              directory containing dir: each directory  name  in  CDPATH  is  searched  for  dir.
              Alternative  directory  names  in  CDPATH  are  separated  by  a colon (:).  A null
              directory name in CDPATH is the same as the current directory, i.e., ``.''.  If dir
              begins  with  a slash (/), then CDPATH is not used.  The -P option causes cd to use
              the physical directory structure by resolving symbolic links while  traversing  dir
              and  before  processing  instances  of .. in dir (see also the -P option to the set
              builtin command); the -L option forces symbolic links to be followed  by  resolving
              the  link  after  processing  instances  of .. in dir.  If .. appears in dir, it is
              processed by removing the immediately previous pathname component from dir, back to
              a  slash  or  the  beginning of dir.  If the -e option is supplied with -P, and the
              current working directory cannot be  successfully  determined  after  a  successful
              directory  change,  cd will return an unsuccessful status.  On systems that support
              it, the -@ option presents the extended attributes associated  with  a  file  as  a
              directory.  An argument of - is converted to $OLDPWD before the directory change is
              attempted.  If a non-empty directory name from CDPATH is used, or if - is the first
              argument,  and the directory change is successful, the absolute pathname of the new
              working directory is written to the standard output.  If the  directory  change  is
              successful,  cd sets the value of the PWD environment variable to the new directory
              name, and sets the OLDPWD environment variable to the value of the current  working
              directory  before  the  change.   The  return  value  is  true if the directory was
              successfully changed; false otherwise.

       command [-pVv] command [arg ...]
              Run command with args suppressing the normal shell function lookup.   Only  builtin
              commands  or  commands  found in the PATH are executed.  If the -p option is given,
              the search for command is  performed  using  a  default  value  for  PATH  that  is
              guaranteed to find all of the standard utilities.  If either the -V or -v option is
              supplied, a description of command is printed.  The -v option causes a single  word
              indicating  the  command or filename used to invoke command to be displayed; the -V
              option produces a more verbose description.  If the -V or -v  option  is  supplied,
              the  exit  status  is  0  if command was found, and 1 if not.  If neither option is
              supplied and an error occurred or command cannot be found, the exit status is  127.
              Otherwise, the exit status of the command builtin is the exit status of command.

       compgen [option] [word]
              Generate  possible  completion matches for word according to the options, which may
              be any option accepted by the complete builtin with the exception of -p and -r, and
              write  the  matches  to  the standard output.  When using the -F or -C options, the
              various shell variables  set  by  the  programmable  completion  facilities,  while
              available, will not have useful values.

              The  matches  will  be  generated in the same way as if the programmable completion
              code had generated them directly from a  completion  specification  with  the  same
              flags.   If  word  is  specified,  only  those  completions  matching  word will be
              displayed.

              The return value is true unless an invalid option is supplied, or no  matches  were
              generated.

       complete [-abcdefgjksuv] [-o comp-option] [-DEI] [-A action] [-G globpat] [-W wordlist]
              [-F function] [-C command] [-X filterpat] [-P prefix] [-S suffix] name [name ...]
       complete -pr [-DEI] [name ...]
              Specify  how  arguments  to  each  name  should  be completed.  If the -p option is
              supplied, or if no options are supplied,  existing  completion  specifications  are
              printed  in  a way that allows them to be reused as input.  The -r option removes a
              completion specification  for  each  name,  or,  if  no  names  are  supplied,  all
              completion specifications.  The -D option indicates that other supplied options and
              actions should apply to the ``default'' command  completion;  that  is,  completion
              attempted on a command for which no completion has previously been defined.  The -E
              option indicates that other supplied options and actions should apply to  ``empty''
              command  completion;  that is, completion attempted on a blank line.  The -I option
              indicates that other supplied options and actions should apply to completion on the
              initial  non-assignment word on the line, or after a command delimiter such as ; or
              |, which is usually command name completion.  If multiple options are supplied, the
              -D  option  takes  precedence over -E, and both take precedence over -I.  If any of
              -D, -E, or -I are supplied, any other name arguments are ignored; these completions
              only apply to the case specified by the option.

              The  process  of  applying  these completion specifications when word completion is
              attempted is described above under Programmable Completion.

              Other options, if specified, have the following meanings.  The arguments to the -G,
              -W,  and  -X options (and, if necessary, the -P and -S options) should be quoted to
              protect them from expansion before the complete builtin is invoked.
              -o comp-option
                      The comp-option controls several aspects of the compspec's behavior  beyond
                      the simple generation of completions.  comp-option may be one of:
                      bashdefault
                              Perform  the  rest  of the default bash completions if the compspec
                              generates no matches.
                      default Use  readline's  default  filename  completion  if   the   compspec
                              generates no matches.
                      dirnames
                              Perform  directory  name  completion  if  the compspec generates no
                              matches.
                      filenames
                              Tell readline that the compspec  generates  filenames,  so  it  can
                              perform  any  filename-specific  processing (like adding a slash to
                              directory  names,  quoting  special  characters,   or   suppressing
                              trailing spaces).  Intended to be used with shell functions.
                      noquote Tell  readline  not  to  quote  the  completed  words  if  they are
                              filenames (quoting filenames is the default).
                      nosort  Tell  readline  not  to  sort  the  list  of  possible  completions
                              alphabetically.
                      nospace Tell  readline  not  to  append  a  space  (the  default)  to words
                              completed at the end of the line.
                      plusdirs
                              After any matches defined by the compspec are generated,  directory
                              name  completion  is  attempted  and  any  matches are added to the
                              results of the other actions.
              -A action
                      The action may be one of the following  to  generate  a  list  of  possible
                      completions:
                      alias   Alias names.  May also be specified as -a.
                      arrayvar
                              Array variable names.
                      binding Readline key binding names.
                      builtin Names of shell builtin commands.  May also be specified as -b.
                      command Command names.  May also be specified as -c.
                      directory
                              Directory names.  May also be specified as -d.
                      disabled
                              Names of disabled shell builtins.
                      enabled Names of enabled shell builtins.
                      export  Names of exported shell variables.  May also be specified as -e.
                      file    File names.  May also be specified as -f.
                      function
                              Names of shell functions.
                      group   Group names.  May also be specified as -g.
                      helptopic
                              Help topics as accepted by the help builtin.
                      hostname
                              Hostnames,  as  taken from the file specified by the HOSTFILE shell
                              variable.
                      job     Job names, if job control is active.  May also be specified as -j.
                      keyword Shell reserved words.  May also be specified as -k.
                      running Names of running jobs, if job control is active.
                      service Service names.  May also be specified as -s.
                      setopt  Valid arguments for the -o option to the set builtin.
                      shopt   Shell option names as accepted by the shopt builtin.
                      signal  Signal names.
                      stopped Names of stopped jobs, if job control is active.
                      user    User names.  May also be specified as -u.
                      variable
                              Names of all shell variables.  May also be specified as -v.
              -C command
                      command is executed in a subshell environment, and its output  is  used  as
                      the possible completions.  Arguments are passed as with the -F option.
              -F function
                      The  shell  function function is executed in the current shell environment.
                      When the function is executed, the first argument ($1) is the name  of  the
                      command  whose  arguments  are being completed, the second argument ($2) is
                      the word being completed, and the third argument ($3) is the word preceding
                      the  word  being  completed on the current command line.  When it finishes,
                      the possible completions are retrieved from  the  value  of  the  COMPREPLY
                      array variable.
              -G globpat
                      The pathname expansion pattern globpat is expanded to generate the possible
                      completions.
              -P prefix
                      prefix is added at the beginning of  each  possible  completion  after  all
                      other options have been applied.
              -S suffix
                      suffix is appended to each possible completion after all other options have
                      been applied.
              -W wordlist
                      The wordlist is split using the characters in the IFS special  variable  as
                      delimiters,  and each resultant word is expanded.  Shell quoting is honored
                      within wordlist, in order to provide a mechanism for the words  to  contain
                      shell  metacharacters  or  characters  in  the  value of IFS.  The possible
                      completions are the members of the resultant  list  which  match  the  word
                      being completed.
              -X filterpat
                      filterpat  is  a  pattern as used for pathname expansion.  It is applied to
                      the list of possible completions generated by  the  preceding  options  and
                      arguments, and each completion matching filterpat is removed from the list.
                      A leading ! in filterpat negates the pattern; in this case, any  completion
                      not matching filterpat is removed.

              The return value is true unless an invalid option is supplied, an option other than
              -p or -r is supplied without a name argument,  an  attempt  is  made  to  remove  a
              completion  specification for a name for which no specification exists, or an error
              occurs adding a completion specification.

       compopt [-o option] [-DEI] [+o option] [name]
              Modify completion options for each name  according  to  the  options,  or  for  the
              currently-executing  completion if no names are supplied.  If no options are given,
              display the completion options for  each  name  or  the  current  completion.   The
              possible values of option are those valid for the complete builtin described above.
              The -D option indicates that other supplied options should apply to the ``default''
              command  completion;  that  is,  completion  attempted  on  a  command for which no
              completion has previously  been  defined.   The  -E  option  indicates  that  other
              supplied  options should apply to ``empty'' command completion; that is, completion
              attempted on a blank line.  The -I option indicates  that  other  supplied  options
              should apply to completion on the initial non-assignment word on the line, or after
              a command delimiter such as ; or |, which is usually command name completion.

              The return value is true unless an invalid option is supplied, an attempt  is  made
              to  modify  the options for a name for which no completion specification exists, or
              an output error occurs.

       continue [n]
              Resume the next iteration of the enclosing for, while, until, or select loop.  If n
              is  specified,  resume  at the nth enclosing loop.  n must be ≥ 1.  If n is greater
              than the number of enclosing loops, the  last  enclosing  loop  (the  ``top-level''
              loop)  is  resumed.  The return value is 0 unless n is not greater than or equal to
              1.

       declare [-aAfFgiIlnrtux] [-p] [name[=value] ...]
       typeset [-aAfFgiIlnrtux] [-p] [name[=value] ...]
              Declare variables and/or give them attributes.  If no names are given then  display
              the  values  of variables.  The -p option will display the attributes and values of
              each name.  When -p is used with name arguments, additional options, other than  -f
              and  -F,  are ignored.  When -p is supplied without name arguments, it will display
              the attributes and values of all variables having the attributes specified  by  the
              additional options.  If no other options are supplied with -p, declare will display
              the attributes and values of all shell variables.  The -f option will restrict  the
              display  to  shell  functions.   The  -F  option  inhibits  the display of function
              definitions; only the function name and attributes are printed.   If  the  extdebug
              shell  option  is  enabled  using shopt, the source file name and line number where
              each name is defined are displayed as well.  The -F  option  implies  -f.   The  -g
              option  forces  variables  to be created or modified at the global scope, even when
              declare is executed in a shell function.  It is ignored in all other cases.  The -I
              option  causes  local  variables  to  inherit  the  attributes  (except the nameref
              attribute) and value of any existing variable with the same name at  a  surrounding
              scope.   If  there  is no existing variable, the local variable is initially unset.
              The following options can  be  used  to  restrict  output  to  variables  with  the
              specified attribute or to give variables attributes:
              -a     Each name is an indexed array variable (see Arrays above).
              -A     Each name is an associative array variable (see Arrays above).
              -f     Use function names only.
              -i     The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC
                     EVALUATION above) is performed when the variable is assigned a value.
              -l     When the variable  is  assigned  a  value,  all  upper-case  characters  are
                     converted to lower-case.  The upper-case attribute is disabled.
              -n     Give  each name the nameref attribute, making it a name reference to another
                     variable.  That other variable  is  defined  by  the  value  of  name.   All
                     references,  assignments,  and attribute modifications to name, except those
                     using or changing the -n attribute itself, are  performed  on  the  variable
                     referenced  by  name's  value.   The  nameref attribute cannot be applied to
                     array variables.
              -r     Make names  readonly.   These  names  cannot  then  be  assigned  values  by
                     subsequent assignment statements or unset.
              -t     Give  each name the trace attribute.  Traced functions inherit the DEBUG and
                     RETURN traps from the calling shell.  The trace  attribute  has  no  special
                     meaning for variables.
              -u     When  the  variable  is  assigned  a  value,  all  lower-case characters are
                     converted to upper-case.  The lower-case attribute is disabled.
              -x     Mark names for export to subsequent commands via the environment.

              Using `+' instead of `-' turns off the attribute instead, with the exceptions  that
              +a  and  +A  may  not be used to destroy array variables and +r will not remove the
              readonly attribute.  When used in a function, declare and typeset  make  each  name
              local,  as with the local command, unless the -g option is supplied.  If a variable
              name is followed by =value, the value of the variable is set to value.  When  using
              -a  or  -A and the compound assignment syntax to create array variables, additional
              attributes do not take effect until subsequent assignments.  The return value is  0
              unless  an  invalid  option is encountered, an attempt is made to define a function
              using ``-f foo=bar'', an attempt is made to assign a value to a readonly  variable,
              an  attempt  is  made  to  assign  a  value  to an array variable without using the
              compound assignment syntax (see Arrays above), one of the  names  is  not  a  valid
              shell  variable name, an attempt is made to turn off readonly status for a readonly
              variable, an attempt is made to turn off array status for an array variable, or  an
              attempt is made to display a non-existent function with -f.

       dirs [-clpv] [+n] [-n]
              Without  options,  displays  the  list  of  currently  remembered directories.  The
              default display is on a single line  with  directory  names  separated  by  spaces.
              Directories  are added to the list with the pushd command; the popd command removes
              entries from the list.  The current directory is always the first directory in  the
              stack.
              -c     Clears the directory stack by deleting all of the entries.
              -l     Produces  a  listing using full pathnames; the default listing format uses a
                     tilde to denote the home directory.
              -p     Print the directory stack with one entry per line.
              -v     Print the directory stack with one entry per line, prefixing each entry with
                     its index in the stack.
              +n     Displays the nth entry counting from the left of the list shown by dirs when
                     invoked without options, starting with zero.
              -n     Displays the nth entry counting from the right of the  list  shown  by  dirs
                     when invoked without options, starting with zero.

              The  return value is 0 unless an invalid option is supplied or n indexes beyond the
              end of the directory stack.

       disown [-ar] [-h] [jobspec ... | pid ... ]
              Without options, remove each jobspec from the table of active jobs.  If jobspec  is
              not  present,  and neither the -a nor the -r option is supplied, the current job is
              used.  If the -h option is given, each jobspec is not removed from the  table,  but
              is marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP.  If
              no jobspec is supplied, the -a option means to remove or  mark  all  jobs;  the  -r
              option  without a jobspec argument restricts operation to running jobs.  The return
              value is 0 unless a jobspec does not specify a valid job.

       echo [-neE] [arg ...]
              Output the args, separated by spaces, followed by a newline.  The return status  is
              0  unless  a  write  error  occurs.   If  -n  is specified, the trailing newline is
              suppressed.  If the -e option is given, interpretation of the following  backslash-
              escaped  characters is enabled.  The -E option disables the interpretation of these
              escape characters, even on systems where they  are  interpreted  by  default.   The
              xpg_echo  shell  option  may  be  used to dynamically determine whether or not echo
              expands these escape characters by default.  echo does not interpret -- to mean the
              end of options.  echo interprets the following escape sequences:
              \a     alert (bell)
              \b     backspace
              \c     suppress further output
              \e
              \E     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \0nnn  the  eight-bit  character  whose value is the octal value nnn (zero to three
                     octal digits)
              \xHH   the eight-bit character whose value is the hexadecimal value HH (one or  two
                     hex digits)
              \uHHHH the  Unicode  (ISO/IEC 10646) character whose value is the hexadecimal value
                     HHHH (one to four hex digits)
              \UHHHHHHHH
                     the Unicode (ISO/IEC 10646) character whose value is the  hexadecimal  value
                     HHHHHHHH (one to eight hex digits)

       enable [-a] [-dnps] [-f filename] [name ...]
              Enable  and  disable  builtin  shell  commands.   Disabling a builtin allows a disk
              command which has the  same  name  as  a  shell  builtin  to  be  executed  without
              specifying  a  full  pathname, even though the shell normally searches for builtins
              before disk commands.  If -n is used, each name is disabled; otherwise,  names  are
              enabled.   For  example,  to  use the test binary found via the PATH instead of the
              shell builtin version, run ``enable -n test''.  The -f option means to load the new
              builtin  command  name from shared object filename, on systems that support dynamic
              loading.  Bash will use the value of the BASH_LOADABLES_PATH variable as  a  colon-
              separated  list  of  directories  in  which to search for filename.  The default is
              system-dependent.  The -d option will delete a builtin previously loaded  with  -f.
              If  no  name  arguments are given, or if the -p option is supplied, a list of shell
              builtins is printed.  With no other option arguments,  the  list  consists  of  all
              enabled shell builtins.  If -n is supplied, only disabled builtins are printed.  If
              -a is supplied, the list printed includes  all  builtins,  with  an  indication  of
              whether or not each is enabled.  If -s is supplied, the output is restricted to the
              POSIX special builtins.  If no options are supplied and  a  name  is  not  a  shell
              builtin,  enable  will  attempt to load name from a shared object named name, as if
              the command were ``enable -f name name .  The return value is 0 unless  a  name  is
              not  a  shell  builtin  or  there  is  an error loading a new builtin from a shared
              object.

       eval [arg ...]
              The args are read and concatenated together into a single command.  This command is
              then  read  and executed by the shell, and its exit status is returned as the value
              of eval.  If there are no args, or only null arguments, eval returns 0.

       exec [-cl] [-a name] [command [arguments]]
              If command is specified, it replaces the shell.  No new process  is  created.   The
              arguments become the arguments to command.  If the -l option is supplied, the shell
              places a dash at the beginning of the zeroth argument passed to command.   This  is
              what  login(1)  does.   The  -c  option causes command to be executed with an empty
              environment.  If -a is supplied, the shell passes name as the  zeroth  argument  to
              the  executed  command.   If  command  cannot  be  executed for some reason, a non-
              interactive shell exits, unless the execfail shell  option  is  enabled.   In  that
              case,  it returns failure.  An interactive shell returns failure if the file cannot
              be executed.  A subshell exits unconditionally if exec fails.  If  command  is  not
              specified, any redirections take effect in the current shell, and the return status
              is 0.  If there is a redirection error, the return status is 1.

       exit [n]
              Cause the shell to exit with a status of n.  If n is omitted, the  exit  status  is
              that  of  the  last  command executed.  A trap on EXIT is executed before the shell
              terminates.

       export [-fn] [name[=word]] ...
       export -p
              The  supplied  names  are  marked  for  automatic  export  to  the  environment  of
              subsequently  executed  commands.   If  the  -f option is given, the names refer to
              functions.  If no names are given, or if the -p option is supplied, a list of names
              of  all exported variables is printed.  The -n option causes the export property to
              be removed from each name.  If a variable name is followed by =word, the  value  of
              the  variable is set to word.  export returns an exit status of 0 unless an invalid
              option is encountered, one of the names is not a valid shell variable name,  or  -f
              is supplied with a name that is not a function.

       fc [-e ename] [-lnr] [first] [last]
       fc -s [pat=rep] [cmd]
              The first form selects a range of commands from first to last from the history list
              and displays or edits and re-executes them.  First and last may be specified  as  a
              string  (to  locate the last command beginning with that string) or as a number (an
              index into the history list, where a negative number is used as an offset from  the
              current  command  number).   When listing, a first or last of 0 is equivalent to -1
              and -0 is equivalent to the current command (usually the fc command);  otherwise  0
              is  equivalent to -1 and -0 is invalid.  If last is not specified, it is set to the
              current command for listing (so that ``fc -l -10'' prints the last 10 commands) and
              to  first  otherwise.  If first is not specified, it is set to the previous command
              for editing and -16 for listing.

              The -n option suppresses the command numbers when listing.  The -r option  reverses
              the  order  of the commands.  If the -l option is given, the commands are listed on
              standard output.  Otherwise, the editor  given  by  ename  is  invoked  on  a  file
              containing those commands.  If ename is not given, the value of the FCEDIT variable
              is used, and the value of EDITOR if FCEDIT is not set.  If neither variable is set,
              vi is used.  When editing is complete, the edited commands are echoed and executed.

              In  the  second form, command is re-executed after each instance of pat is replaced
              by rep.  Command is interpreted the same as first above.  A  useful  alias  to  use
              with this is ``r="fc -s"'', so that typing ``r cc'' runs the last command beginning
              with ``cc'' and typing ``r'' re-executes the last command.

              If the first form is used, the return value  is  0  unless  an  invalid  option  is
              encountered  or first or last specify history lines out of range.  If the -e option
              is supplied, the return value is the value of the last command executed or  failure
              if  an  error  occurs  with  the temporary file of commands.  If the second form is
              used, the return status is that of the command re-executed,  unless  cmd  does  not
              specify a valid history line, in which case fc returns failure.

       fg [jobspec]
              Resume  jobspec  in the foreground, and make it the current job.  If jobspec is not
              present, the shell's notion of the current job is used.  The return value  is  that
              of  the  command  placed into the foreground, or failure if run when job control is
              disabled or, when run with job control enabled, if jobspec does not specify a valid
              job or jobspec specifies a job that was started without job control.

       getopts optstring name [arg ...]
              getopts  is  used  by  shell  procedures to parse positional parameters.  optstring
              contains the option characters to be recognized; if a character is  followed  by  a
              colon,  the  option is expected to have an argument, which should be separated from
              it by white space.  The colon and question mark  characters  may  not  be  used  as
              option  characters.  Each time it is invoked, getopts places the next option in the
              shell variable name, initializing name if it does not exist, and the index  of  the
              next argument to be processed into the variable OPTIND.  OPTIND is initialized to 1
              each time the shell or a shell script is  invoked.   When  an  option  requires  an
              argument,  getopts  places  that argument into the variable OPTARG.  The shell does
              not reset OPTIND automatically; it must be manually reset between multiple calls to
              getopts within the same shell invocation if a new set of parameters is to be used.

              When  the  end of options is encountered, getopts exits with a return value greater
              than zero.  OPTIND is set to the index of the first non-option argument,  and  name
              is set to ?.

              getopts  normally  parses  the  positional  parameters,  but  if more arguments are
              supplied as arg values, getopts parses those instead.

              getopts can report errors in two ways.  If the first character of  optstring  is  a
              colon,  silent  error  reporting is used.  In normal operation, diagnostic messages
              are printed when invalid options or missing option arguments are  encountered.   If
              the  variable  OPTERR is set to 0, no error messages will be displayed, even if the
              first character of optstring is not a colon.

              If an invalid option is seen, getopts places ? into name and, if not silent, prints
              an  error  message  and  unsets OPTARG.  If getopts is silent, the option character
              found is placed in OPTARG and no diagnostic message is printed.

              If a required argument is not found, and getopts is not silent, a question mark (?)
              is  placed  in  name,  OPTARG  is  unset,  and a diagnostic message is printed.  If
              getopts is silent, then a colon (:) is placed in name and  OPTARG  is  set  to  the
              option character found.

              getopts  returns true if an option, specified or unspecified, is found.  It returns
              false if the end of options is encountered or an error occurs.

       hash [-lr] [-p filename] [-dt] [name]
              Each time hash is invoked, the full pathname of the command name is  determined  by
              searching  the  directories  in  $PATH  and  remembered.  Any previously-remembered
              pathname is discarded.  If the -p option is supplied, no path search is  performed,
              and filename is used as the full filename of the command.  The -r option causes the
              shell to forget all remembered locations.  The -d option causes the shell to forget
              the  remembered  location  of  each  name.   If the -t option is supplied, the full
              pathname to which each name corresponds is printed.  If multiple name arguments are
              supplied  with  -t,  the  name  is printed before the hashed full pathname.  The -l
              option causes output to be displayed in a format that may be reused as  input.   If
              no  arguments  are  given,  or if only -l is supplied, information about remembered
              commands is printed.  The return status is true unless a name is not  found  or  an
              invalid option is supplied.

       help [-dms] [pattern]
              Display  helpful information about builtin commands.  If pattern is specified, help
              gives detailed help on all commands matching pattern; otherwise help  for  all  the
              builtins and shell control structures is printed.
              -d     Display a short description of each pattern
              -m     Display the description of each pattern in a manpage-like format
              -s     Display only a short usage synopsis for each pattern

              The return status is 0 unless no command matches pattern.

       history [n]
       history -c
       history -d offset
       history -d start-end
       history -anrw [filename]
       history -p arg [arg ...]
       history -s arg [arg ...]
              With  no options, display the command history list with line numbers.  Lines listed
              with a * have been modified.  An argument of n lists only the last n lines.  If the
              shell  variable  HISTTIMEFORMAT  is set and not null, it is used as a format string
              for strftime(3) to display the time stamp associated with  each  displayed  history
              entry.   No  intervening  blank is printed between the formatted time stamp and the
              history line.  If filename is supplied, it is used as the name of the history file;
              if  not,  the  value of HISTFILE is used.  Options, if supplied, have the following
              meanings:
              -c     Clear the history list by deleting all the entries.
              -d offset
                     Delete the history entry at position offset.  If offset is negative,  it  is
                     interpreted  as  relative  to one greater than the last history position, so
                     negative indices count back from the end of the history, and an index of  -1
                     refers to the current history -d command.
              -d start-end
                     Delete  the  range  of  history  entries  between  positions  start and end,
                     inclusive.  Positive and negative values for start and end  are  interpreted
                     as described above.
              -a     Append  the  ``new''  history  lines to the history file.  These are history
                     lines entered since the beginning of  the  current  bash  session,  but  not
                     already appended to the history file.
              -n     Read  the  history  lines  not  already  read from the history file into the
                     current history list.  These are lines appended to the  history  file  since
                     the beginning of the current bash session.
              -r     Read the contents of the history file and append them to the current history
                     list.
              -w     Write the current history list to the history file, overwriting the  history
                     file's contents.
              -p     Perform history substitution on the following args and display the result on
                     the standard output.  Does not store the results in the history list.   Each
                     arg must be quoted to disable normal history expansion.
              -s     Store  the  args in the history list as a single entry.  The last command in
                     the history list is removed before the args are added.

              If the HISTTIMEFORMAT variable is set, the time stamp information  associated  with
              each  history entry is written to the history file, marked with the history comment
              character.  When the history file is read, lines beginning with the history comment
              character  followed  immediately  by  a digit are interpreted as timestamps for the
              following history entry.  The return  value  is  0  unless  an  invalid  option  is
              encountered,  an error occurs while reading or writing the history file, an invalid
              offset or range is supplied as an argument to -d, or the history expansion supplied
              as an argument to -p fails.

       jobs [-lnprs] [ jobspec ... ]
       jobs -x command [ args ... ]
              The first form lists the active jobs.  The options have the following meanings:
              -l     List process IDs in addition to the normal information.
              -n     Display  information only about jobs that have changed status since the user
                     was last notified of their status.
              -p     List only the process ID of the job's process group leader.
              -r     Display only running jobs.
              -s     Display only stopped jobs.

              If jobspec is given, output is restricted  to  information  about  that  job.   The
              return status is 0 unless an invalid option is encountered or an invalid jobspec is
              supplied.

              If the -x option is supplied, jobs replaces any jobspec found in  command  or  args
              with  the  corresponding  process  group  ID, and executes command passing it args,
              returning its exit status.

       kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
       kill -l|-L [sigspec | exit_status]
              Send the signal named by sigspec or  signum  to  the  processes  named  by  pid  or
              jobspec.  sigspec is either a case-insensitive signal name such as SIGKILL (with or
              without the SIG prefix) or a signal number; signum is a signal number.  If  sigspec
              is not present, then SIGTERM is assumed.  An argument of -l lists the signal names.
              If any arguments  are  supplied  when  -l  is  given,  the  names  of  the  signals
              corresponding  to  the  arguments  are  listed,  and  the  return status is 0.  The
              exit_status argument to -l is a number specifying either a  signal  number  or  the
              exit  status  of  a process terminated by a signal.  The -L option is equivalent to
              -l.  kill returns true if at least one signal was successfully sent, or false if an
              error occurs or an invalid option is encountered.

       let arg [arg ...]
              Each  arg  is  an  arithmetic expression to be evaluated (see ARITHMETIC EVALUATION
              above).  If the last arg evaluates to 0, let returns 1; 0 is returned otherwise.

       local [option] [name[=value] ... | - ]
              For each argument, a local variable named name is created, and assigned value.  The
              option  can be any of the options accepted by declare.  When local is used within a
              function, it causes the variable name to have a visible scope  restricted  to  that
              function and its children.  If name is -, the set of shell options is made local to
              the function in which local is invoked: shell options changed using the set builtin
              inside  the  function  are  restored  to  their  original  values when the function
              returns.  The restore is effected as if a series of set commands were  executed  to
              restore the values that were in place before the function.  With no operands, local
              writes a list of local variables to the standard output.  It is  an  error  to  use
              local  when  not  within  a  function.  The return status is 0 unless local is used
              outside a function, an invalid name is supplied, or name is a readonly variable.

       logout Exit a login shell.

       mapfile [-d delim] [-n count] [-O origin] [-s  count]  [-t]  [-u  fd]  [-C  callback]  [-c
       quantum] [array]
       readarray  [-d  delim]  [-n  count]  [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c
       quantum] [array]
              Read lines from the standard input into the indexed array variable array,  or  from
              file  descriptor  fd  if  the  -u  option is supplied.  The variable MAPFILE is the
              default array.  Options, if supplied, have the following meanings:
              -d     The first character of delim is used to terminate each  input  line,  rather
                     than  newline.   If delim is the empty string, mapfile will terminate a line
                     when it reads a NUL character.
              -n     Copy at most count lines.  If count is 0, all lines are copied.
              -O     Begin assigning to array at index origin.  The default index is 0.
              -s     Discard the first count lines read.
              -t     Remove a trailing delim (default newline) from each line read.
              -u     Read lines from file descriptor fd instead of the standard input.
              -C     Evaluate callback each time quantum lines are read.  The -c option specifies
                     quantum.
              -c     Specify the number of lines read between each call to callback.

              If  -C  is  specified  without  -c,  the default quantum is 5000.  When callback is
              evaluated, it is supplied the index of the next array element to  be  assigned  and
              the  line  to  be  assigned  to  that element as additional arguments.  callback is
              evaluated after the line is read but before the array element is assigned.

              If not supplied with an explicit origin, mapfile will clear array before  assigning
              to it.

              mapfile  returns  successfully  unless  an  invalid  option  or  option argument is
              supplied, array is invalid or unassignable, or if array is not an indexed array.

       popd [-n] [+n] [-n]
              Removes entries from the  directory  stack.   The  elements  are  numbered  from  0
              starting  at  the  first directory listed by dirs.  With no arguments, popd removes
              the top directory from the stack, and changes to the new top directory.  Arguments,
              if supplied, have the following meanings:
              -n     Suppresses the normal change of directory when removing directories from the
                     stack, so that only the stack is manipulated.
              +n     Removes the nth entry counting from the left of  the  list  shown  by  dirs,
                     starting  with  zero,  from the stack.  For example: ``popd +0'' removes the
                     first directory, ``popd +1'' the second.
              -n     Removes the nth entry counting from the right of the  list  shown  by  dirs,
                     starting  with  zero.   For example: ``popd -0'' removes the last directory,
                     ``popd -1'' the next to last.

              If the top element of the directory stack is modified, and the -n  option  was  not
              supplied,  popd  uses  the  cd builtin to change to the directory at the top of the
              stack.  If the cd fails, popd returns a non-zero value.

              Otherwise, popd returns false if an invalid option is  encountered,  the  directory
              stack is empty, or a non-existent directory stack entry is specified.

              If the popd command is successful, bash runs dirs to show the final contents of the
              directory stack, and the return status is 0.

       printf [-v var] format [arguments]
              Write the formatted arguments to the standard  output  under  the  control  of  the
              format.   The -v option causes the output to be assigned to the variable var rather
              than being printed to the standard output.

              The format is a character string which  contains  three  types  of  objects:  plain
              characters, which are simply copied to standard output, character escape sequences,
              which are converted and copied to the standard output, and  format  specifications,
              each  of which causes printing of the next successive argument.  In addition to the
              standard  printf(1)  format  specifications,  printf   interprets   the   following
              extensions:
              %b     causes  printf  to  expand  backslash  escape sequences in the corresponding
                     argument in the same way as echo -e.
              %q     causes printf to output the corresponding argument in a format that  can  be
                     reused as shell input.
              %Q     like  %q,  but applies any supplied precision to the argument before quoting
                     it.
              %(datefmt)T
                     causes printf to output the date-time string resulting from using datefmt as
                     a  format  string for strftime(3).  The corresponding argument is an integer
                     representing the number of seconds since the epoch.   Two  special  argument
                     values  may  be  used: -1 represents the current time, and -2 represents the
                     time the shell was invoked.  If no argument is specified, conversion behaves
                     as if -1 had been given.  This is an exception to the usual printf behavior.

              The  %b, %q, and %T directives all use the field width and precision arguments from
              the format specification and write that many bytes from (or use that wide  a  field
              for)  the  expanded  argument,  which  usually  contains  more  characters than the
              original.

              Arguments to non-string format specifiers are treated as C constants, except that a
              leading  plus or minus sign is allowed, and if the leading character is a single or
              double quote, the value is the ASCII value of the following character.

              The format is reused as necessary to consume all of the arguments.  If  the  format
              requires  more  arguments than are supplied, the extra format specifications behave
              as if a zero value or null string, as appropriate, had been supplied.   The  return
              value is zero on success, non-zero on failure.

       pushd [-n] [+n] [-n]
       pushd [-n] [dir]
              Adds  a  directory  to the top of the directory stack, or rotates the stack, making
              the new top of the stack the current working directory.  With no  arguments,  pushd
              exchanges  the  top  two  elements of the directory stack.  Arguments, if supplied,
              have the following meanings:
              -n     Suppresses  the  normal  change  of  directory  when  rotating   or   adding
                     directories to the stack, so that only the stack is manipulated.
              +n     Rotates  the  stack so that the nth directory (counting from the left of the
                     list shown by dirs, starting with zero) is at the top.
              -n     Rotates the stack so that the nth directory (counting from the right of  the
                     list shown by dirs, starting with zero) is at the top.
              dir    Adds dir to the directory stack at the top

              After  the  stack  has been modified, if the -n option was not supplied, pushd uses
              the cd builtin to change to the directory at the top  of  the  stack.   If  the  cd
              fails, pushd returns a non-zero value.

              Otherwise, if no arguments are supplied, pushd returns 0 unless the directory stack
              is empty.  When rotating the directory stack, pushd returns 0 unless the  directory
              stack is empty or a non-existent directory stack element is specified.

              If  the  pushd  command is successful, bash runs dirs to show the final contents of
              the directory stack.

       pwd [-LP]
              Print the absolute pathname of the current working directory.  The pathname printed
              contains  no  symbolic links if the -P option is supplied or the -o physical option
              to the set builtin command is enabled.  If the -L  option  is  used,  the  pathname
              printed  may contain symbolic links.  The return status is 0 unless an error occurs
              while reading the name of the current directory or an invalid option is supplied.

       read [-ers] [-a aname] [-d delim] [-i text]  [-n  nchars]  [-N  nchars]  [-p  prompt]  [-t
       timeout] [-u fd] [name ...]
              One  line  is read from the standard input, or from the file descriptor fd supplied
              as an argument to the -u option, split into words as  described  above  under  Word
              Splitting, and the first word is assigned to the first name, the second word to the
              second name, and so on.  If there are more words than names,  the  remaining  words
              and their intervening delimiters are assigned to the last name.  If there are fewer
              words read from the input stream than names, the remaining names are assigned empty
              values.  The characters in IFS are used to split the line into words using the same
              rules the shell uses for expansion (described above  under  Word  Splitting).   The
              backslash  character  (\)  may  be  used to remove any special meaning for the next
              character read and for line continuation.  Options, if supplied, have the following
              meanings:
              -a aname
                     The  words  are  assigned to sequential indices of the array variable aname,
                     starting at 0.  aname is unset before any new values  are  assigned.   Other
                     name arguments are ignored.
              -d delim
                     The  first  character  of  delim is used to terminate the input line, rather
                     than newline.  If delim is the empty string, read will terminate a line when
                     it reads a NUL character.
              -e     If  the  standard  input  is  coming from a terminal, readline (see READLINE
                     above) is used to obtain the line.  Readline uses the current  (or  default,
                     if  line  editing  was  not  previously  active)  editing settings, but uses
                     readline's default filename completion.
              -i text
                     If readline is being used to read the line, text is placed into the  editing
                     buffer before editing begins.
              -n nchars
                     read  returns  after  reading  nchars  characters  rather than waiting for a
                     complete line of  input,  but  honors  a  delimiter  if  fewer  than  nchars
                     characters are read before the delimiter.
              -N nchars
                     read returns after reading exactly nchars characters rather than waiting for
                     a complete line of input, unless EOF  is  encountered  or  read  times  out.
                     Delimiter  characters encountered in the input are not treated specially and
                     do not cause read to return until nchars characters are read.  The result is
                     not  split  on  the  characters  in  IFS; the intent is that the variable is
                     assigned exactly the characters read (with the exception of  backslash;  see
                     the -r option below).
              -p prompt
                     Display  prompt  on  standard  error,  without  a  trailing  newline, before
                     attempting to read any input.  The prompt is  displayed  only  if  input  is
                     coming from a terminal.
              -r     Backslash  does not act as an escape character.  The backslash is considered
                     to be part of the line.  In particular, a  backslash-newline  pair  may  not
                     then be used as a line continuation.
              -s     Silent mode.  If input is coming from a terminal, characters are not echoed.
              -t timeout
                     Cause  read to time out and return failure if a complete line of input (or a
                     specified number of characters) is not read within timeout seconds.  timeout
                     may  be  a  decimal  number  with a fractional portion following the decimal
                     point.  This option is only effective  if  read  is  reading  input  from  a
                     terminal,  pipe,  or  other special file; it has no effect when reading from
                     regular files.  If read times out, read saves any partial  input  read  into
                     the  specified  variable  name.   If timeout is 0, read returns immediately,
                     without trying to read any data.  The exit status is 0 if input is available
                     on  the  specified  file  descriptor,  or the read will return EOF, non-zero
                     otherwise.  The exit status is greater than 128 if the timeout is exceeded.
              -u fd  Read input from file descriptor fd.

              If no names are supplied, the line read, without the ending delimiter but otherwise
              unmodified,  is  assigned  to  the variable REPLY.  The exit status is zero, unless
              end-of-file is encountered, read times out (in which case  the  status  is  greater
              than  128),  a variable assignment error (such as assigning to a readonly variable)
              occurs, or an invalid file descriptor is supplied as the argument to -u.

       readonly [-aAf] [-p] [name[=word] ...]
              The given names are marked readonly; the values of these names may not  be  changed
              by   subsequent   assignment.    If  the  -f  option  is  supplied,  the  functions
              corresponding to the names are so marked.  The -a option restricts the variables to
              indexed  arrays;  the  -A option restricts the variables to associative arrays.  If
              both options are supplied, -A takes precedence.  If no name arguments are given, or
              if  the  -p option is supplied, a list of all readonly names is printed.  The other
              options may be used to restrict the output to a  subset  of  the  set  of  readonly
              names.   The -p option causes output to be displayed in a format that may be reused
              as input.  If a variable name is followed by =word, the value of  the  variable  is
              set  to  word.  The return status is 0 unless an invalid option is encountered, one
              of the names is not a valid shell variable name, or -f is supplied with a name that
              is not a function.

       return [n]
              Causes  a  function  to  stop  executing and return the value specified by n to its
              caller.  If n is omitted, the return status is that of the last command executed in
              the  function body.  If return is executed by a trap handler, the last command used
              to determine the status is the last command executed before the trap  handler.   If
              return  is  executed  during  a  DEBUG trap, the last command used to determine the
              status is the last command executed by the trap handler before return was  invoked.
              If  return  is  used  outside a function, but during execution of a script by the .
              (source) command, it causes the shell to stop  executing  that  script  and  return
              either  n  or the exit status of the last command executed within the script as the
              exit status of the script.  If n  is  supplied,  the  return  value  is  its  least
              significant  8  bits.   The  return status is non-zero if return is supplied a non-
              numeric argument, or is used outside a function  and  not  during  execution  of  a
              script  by  .  or  source.  Any command associated with the RETURN trap is executed
              before execution resumes after the function or script.

       set [-abefhkmnptuvxBCEHPT] [-o option-name] [--] [-] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [+o option-name] [--] [-] [arg ...]
              Without options, display the name and value of each shell variable in a format that
              can be reused as input for setting or resetting the currently-set variables.  Read-
              only variables cannot be reset.  In posix mode, only shell  variables  are  listed.
              The  output is sorted according to the current locale.  When options are specified,
              they  set  or  unset  shell  attributes.   Any  arguments  remaining  after  option
              processing are treated as values for the positional parameters and are assigned, in
              order, to $1, $2, ...  $n.  Options, if specified, have the following meanings:
              -a      Each variable or function that is created or modified is given  the  export
                      attribute and marked for export to the environment of subsequent commands.
              -b      Report  the  status  of terminated background jobs immediately, rather than
                      before the next primary prompt.  This is effective only when job control is
                      enabled.
              -e      Exit  immediately  if  a  pipeline  (which  may  consist of a single simple
                      command), a list, or a compound command (see SHELL  GRAMMAR  above),  exits
                      with  a non-zero status.  The shell does not exit if the command that fails
                      is part of the command list immediately following a while or until keyword,
                      part  of  the  test  following  the  if or elif reserved words, part of any
                      command executed in a && or || list except the command following the  final
                      &&  or  ||,  any  command  in  a pipeline but the last, or if the command's
                      return value is being inverted with !.  If a compound command other than  a
                      subshell  returns  a  non-zero status because a command failed while -e was
                      being ignored, the shell does not exit.  A trap on ERR, if set, is executed
                      before  the  shell exits.  This option applies to the shell environment and
                      each subshell environment separately  (see  COMMAND  EXECUTION  ENVIRONMENT
                      above),  and  may cause subshells to exit before executing all the commands
                      in the subshell.

                      If a compound command or shell function executes in a context where  -e  is
                      being ignored, none of the commands executed within the compound command or
                      function body will be affected by the -e setting, even if -e is set  and  a
                      command  returns a failure status.  If a compound command or shell function
                      sets -e while executing in a context where -e is ignored, that setting will
                      not  have  any  effect until the compound command or the command containing
                      the function call completes.
              -f      Disable pathname expansion.
              -h      Remember the location of commands as they  are  looked  up  for  execution.
                      This is enabled by default.
              -k      All  arguments  in  the  form  of  assignment  statements are placed in the
                      environment for a command, not just those that precede the command name.
              -m      Monitor mode.  Job control is enabled.  This option is on  by  default  for
                      interactive shells on systems that support it (see JOB CONTROL above).  All
                      processes  run  in  a  separate  process  group.   When  a  background  job
                      completes, the shell prints a line containing its exit status.
              -n      Read  commands  but do not execute them.  This may be used to check a shell
                      script for syntax errors.  This is ignored by interactive shells.
              -o option-name
                      The option-name can be one of the following:
                      allexport
                              Same as -a.
                      braceexpand
                              Same as -B.
                      emacs   Use an emacs-style command line editing interface.  This is enabled
                              by  default  when  the  shell  is  interactive, unless the shell is
                              started with the --noediting option.  This also affects the editing
                              interface used for read -e.
                      errexit Same as -e.
                      errtrace
                              Same as -E.
                      functrace
                              Same as -T.
                      hashall Same as -h.
                      histexpand
                              Same as -H.
                      history Enable  command  history,  as  described above under HISTORY.  This
                              option is on by default in interactive shells.
                      ignoreeof
                              The effect is as if the shell  command  ``IGNOREEOF=10''  had  been
                              executed (see Shell Variables above).
                      keyword Same as -k.
                      monitor Same as -m.
                      noclobber
                              Same as -C.
                      noexec  Same as -n.
                      noglob  Same as -f.
                      nolog   Currently ignored.
                      notify  Same as -b.
                      nounset Same as -u.
                      onecmd  Same as -t.
                      physical
                              Same as -P.
                      pipefail
                              If  set,  the  return  value of a pipeline is the value of the last
                              (rightmost) command to exit with a non-zero status, or zero if  all
                              commands  in  the  pipeline  exit  successfully.   This  option  is
                              disabled by default.
                      posix   Change the behavior of bash where  the  default  operation  differs
                              from  the  POSIX  standard to match the standard (posix mode).  See
                              SEE ALSO below for a reference to a document that details how posix
                              mode affects bash's behavior.
                      privileged
                              Same as -p.
                      verbose Same as -v.
                      vi      Use  a  vi-style command line editing interface.  This also affects
                              the editing interface used for read -e.
                      xtrace  Same as -x.
                      If -o is supplied with no option-name, the values of  the  current  options
                      are  printed.   If  +o  is  supplied  with  no option-name, a series of set
                      commands to recreate the  current  option  settings  is  displayed  on  the
                      standard output.
              -p      Turn  on  privileged  mode.  In this mode, the $ENV and $BASH_ENV files are
                      not processed, shell functions are not inherited from the environment,  and
                      the  SHELLOPTS,  BASHOPTS, CDPATH, and GLOBIGNORE variables, if they appear
                      in the environment,  are  ignored.   If  the  shell  is  started  with  the
                      effective user (group) id not equal to the real user (group) id, and the -p
                      option is not supplied, these actions are taken and the effective  user  id
                      is  set  to the real user id.  If the -p option is supplied at startup, the
                      effective user id is  not  reset.   Turning  this  option  off  causes  the
                      effective user and group ids to be set to the real user and group ids.
              -r      Enable restricted shell mode.  This option cannot be unset once it has been
                      set.
              -t      Exit after reading and executing one command.
              -u      Treat unset variables and parameters other than the special parameters  "@"
                      and  "*",  or array variables subscripted with "@" or "*", as an error when
                      performing parameter expansion.  If expansion  is  attempted  on  an  unset
                      variable  or  parameter,  the  shell  prints  an error message, and, if not
                      interactive, exits with a non-zero status.
              -v      Print shell input lines as they are read.
              -x      After expanding each simple command,  for  command,  case  command,  select
                      command,  or  arithmetic  for  command,  display the expanded value of PS4,
                      followed by the command and its expanded arguments or associated word list.
              -B      The shell performs brace expansion (see Brace Expansion above).  This is on
                      by default.
              -C      If  set,  bash  does  not overwrite an existing file with the >, >&, and <>
                      redirection operators.  This may be overridden when creating  output  files
                      by using the redirection operator >| instead of >.
              -E      If  set,  any  trap  on  ERR  is  inherited  by  shell  functions,  command
                      substitutions, and commands executed in a subshell  environment.   The  ERR
                      trap is normally not inherited in such cases.
              -H      Enable  !   style  history substitution.  This option is on by default when
                      the shell is interactive.
              -P      If set, the shell does not resolve symbolic links when  executing  commands
                      such as cd that change the current working directory.  It uses the physical
                      directory structure instead.  By default, bash follows the logical chain of
                      directories when performing commands which change the current directory.
              -T      If  set,  any  traps  on DEBUG and RETURN are inherited by shell functions,
                      command substitutions, and commands executed  in  a  subshell  environment.
                      The DEBUG and RETURN traps are normally not inherited in such cases.
              --      If  no  arguments  follow  this  option, then the positional parameters are
                      unset.  Otherwise, the positional parameters are set to the args,  even  if
                      some of them begin with a -.
              -       Signal  the  end of options, cause all remaining args to be assigned to the
                      positional parameters.  The -x and -v options are turned off.  If there are
                      no args, the positional parameters remain unchanged.

              The  options  are  off  by  default  unless otherwise noted.  Using + rather than -
              causes these options to be turned off.   The  options  can  also  be  specified  as
              arguments  to  an invocation of the shell.  The current set of options may be found
              in $-.  The return status is always true unless an invalid option is encountered.

       shift [n]
              The positional  parameters  from  n+1  ...  are  renamed  to  $1  ....   Parameters
              represented  by  the numbers $# down to $#-n+1 are unset.  n must be a non-negative
              number less than or equal to $#.  If n is 0, no parameters are changed.   If  n  is
              not  given,  it  is  assumed  to  be  1.   If  n is greater than $#, the positional
              parameters are not changed.  The return status is greater than zero if n is greater
              than $# or less than zero; otherwise 0.

       shopt [-pqsu] [-o] [optname ...]
              Toggle  the  values  of settings controlling optional shell behavior.  The settings
              can be either those listed below, or, if the -o option  is  used,  those  available
              with  the  -o  option  to the set builtin command.  With no options, or with the -p
              option, a list of all settable options is displayed, with an indication of  whether
              or  not  each  is  set; if optnames are supplied, the output is restricted to those
              options.  The -p option causes output to be displayed in a form that may be  reused
              as input.  Other options have the following meanings:
              -s     Enable (set) each optname.
              -u     Disable (unset) each optname.
              -q     Suppresses  normal  output (quiet mode); the return status indicates whether
                     the optname is set or unset.  If multiple optname arguments are  given  with
                     -q,  the  return  status  is  zero  if  all  optnames  are enabled; non-zero
                     otherwise.
              -o     Restricts the values of optname to be those defined for the -o option to the
                     set builtin.

              If  either  -s  or  -u  is  used  with no optname arguments, shopt shows only those
              options which are set or unset, respectively.  Unless otherwise  noted,  the  shopt
              options are disabled (unset) by default.

              The  return  status  when listing options is zero if all optnames are enabled, non-
              zero otherwise.  When setting or unsetting  options,  the  return  status  is  zero
              unless an optname is not a valid shell option.

              The list of shopt options is:

              assoc_expand_once
                      If  set,  the  shell  suppresses  multiple  evaluation of associative array
                      subscripts  during  arithmetic  expression  evaluation,   while   executing
                      builtins  that  can  perform  variable  assignments,  and  while  executing
                      builtins that perform array dereferencing.
              autocd  If set, a command name that is the name of a directory is executed as if it
                      were  the  argument  to  the  cd  command.   This  option  is  only used by
                      interactive shells.
              cdable_vars
                      If set, an argument to the cd builtin command that is not  a  directory  is
                      assumed to be the name of a variable whose value is the directory to change
                      to.
              cdspell If set, minor errors in the spelling of  a  directory  component  in  a  cd
                      command   will  be  corrected.   The  errors  checked  for  are  transposed
                      characters, a  missing  character,  and  one  character  too  many.   If  a
                      correction  is  found,  the  corrected filename is printed, and the command
                      proceeds.  This option is only used by interactive shells.
              checkhash
                      If set, bash checks that a command found in the hash  table  exists  before
                      trying  to execute it.  If a hashed command no longer exists, a normal path
                      search is performed.
              checkjobs
                      If set, bash lists the status  of  any  stopped  and  running  jobs  before
                      exiting  an  interactive  shell.   If any jobs are running, this causes the
                      exit to be deferred until a second exit is attempted without an intervening
                      command (see JOB CONTROL above).  The shell always postpones exiting if any
                      jobs are stopped.
              checkwinsize
                      If set, bash checks the  window  size  after  each  external  (non-builtin)
                      command  and,  if necessary, updates the values of LINES and COLUMNS.  This
                      option is enabled by default.
              cmdhist If set, bash attempts to save all lines of a multiple-line command  in  the
                      same  history  entry.   This allows easy re-editing of multi-line commands.
                      This option is enabled by default,  but  only  has  an  effect  if  command
                      history is enabled, as described above under HISTORY.
              compat31
              compat32
              compat40
              compat41
              compat42
              compat43
              compat44
              compat50
                      These  control  aspects  of  the  shell's  compatibility  mode  (see  SHELL
                      COMPATIBILITY MODE below).

              complete_fullquote
                      If set, bash quotes all shell metacharacters  in  filenames  and  directory
                      names  when performing completion.  If not set, bash removes metacharacters
                      such as the dollar sign from the set of characters that will be  quoted  in
                      completed  filenames  when  these  metacharacters  appear in shell variable
                      references in words to be completed.   This  means  that  dollar  signs  in
                      variable  names that expand to directories will not be quoted; however, any
                      dollar signs appearing in filenames will not be quoted,  either.   This  is
                      active  only  when  bash is using backslashes to quote completed filenames.
                      This variable is set by default, which is  the  default  bash  behavior  in
                      versions through 4.2.

              direxpand
                      If  set,  bash  replaces directory names with the results of word expansion
                      when performing filename completion.  This  changes  the  contents  of  the
                      readline  editing  buffer.   If not set, bash attempts to preserve what the
                      user typed.

              dirspell
                      If set, bash attempts spelling correction on directory  names  during  word
                      completion if the directory name initially supplied does not exist.

              dotglob If  set,  bash  includes  filenames  beginning with a `.' in the results of
                      pathname expansion.  The  filenames  ``.''   and  ``..''   must  always  be
                      matched explicitly, even if dotglob is set.

              execfail
                      If set, a non-interactive shell will not exit if it cannot execute the file
                      specified as an argument to the exec builtin command.  An interactive shell
                      does not exit if exec fails.

              expand_aliases
                      If set, aliases are expanded as described above under ALIASES.  This option
                      is enabled by default for interactive shells.

              extdebug
                      If set at shell invocation, or in a shell startup file, arrange to  execute
                      the  debugger  profile before the shell starts, identical to the --debugger
                      option.  If set after invocation, behavior intended for use by debuggers is
                      enabled:

                      1.     The  -F  option to the declare builtin displays the source file name
                             and line number corresponding to each function name supplied  as  an
                             argument.

                      2.     If  the  command run by the DEBUG trap returns a non-zero value, the
                             next command is skipped and not executed.

                      3.     If the command run by the DEBUG trap returns a value of 2,  and  the
                             shell  is  executing  in  a  subroutine (a shell function or a shell
                             script executed by the . or source builtins), the shell simulates  a
                             call to return.

                      4.     BASH_ARGC   and   BASH_ARGV   are  updated  as  described  in  their
                             descriptions above).

                      5.     Function tracing is enabled: command substitution, shell  functions,
                             and  subshells invoked with ( command ) inherit the DEBUG and RETURN
                             traps.

                      6.     Error tracing is enabled: command substitution, shell functions, and
                             subshells invoked with ( command ) inherit the ERR trap.

              extglob If  set,  the  extended  pattern  matching  features  described above under
                      Pathname Expansion are enabled.

              extquote
                      If set, $'string' and $"string" quoting is  performed  within  ${parameter}
                      expansions enclosed in double quotes.  This option is enabled by default.

              failglob
                      If  set,  patterns  which fail to match filenames during pathname expansion
                      result in an expansion error.

              force_fignore
                      If set, the suffixes specified by the FIGNORE shell variable cause words to
                      be  ignored  when  performing word completion even if the ignored words are
                      the only possible completions.  See SHELL VARIABLES above for a description
                      of FIGNORE.  This option is enabled by default.

              globasciiranges
                      If set, range expressions used in pattern matching bracket expressions (see
                      Pattern Matching above) behave as if  in  the  traditional  C  locale  when
                      performing  comparisons.   That is, the current locale's collating sequence
                      is not taken into account, so b will not  collate  between  A  and  B,  and
                      upper-case and lower-case ASCII characters will collate together.

              globskipdots
                      If  set,  pathname  expansion  will  never  match  the filenames ``.''  and
                      ``..'', even if the pattern begins with a ``.''.  This option is enabled by
                      default.

              globstar
                      If  set, the pattern ** used in a pathname expansion context will match all
                      files and zero or more directories and subdirectories.  If the  pattern  is
                      followed by a /, only directories and subdirectories match.

              gnu_errfmt
                      If  set, shell error messages are written in the standard GNU error message
                      format.

              histappend
                      If set, the history list is appended to the file named by the value of  the
                      HISTFILE variable when the shell exits, rather than overwriting the file.

              histreedit
                      If  set, and readline is being used, a user is given the opportunity to re-
                      edit a failed history substitution.

              histverify
                      If set, and readline is being used, the results of history substitution are
                      not immediately passed to the shell parser.  Instead, the resulting line is
                      loaded into the readline editing buffer, allowing further modification.

              hostcomplete
                      If set, and readline is being used, bash will attempt to  perform  hostname
                      completion  when  a  word containing a @ is being completed (see Completing
                      under READLINE above).  This is enabled by default.

              huponexit
                      If set, bash will send SIGHUP to all jobs when an interactive  login  shell
                      exits.

              inherit_errexit
                      If  set,  command  substitution  inherits  the value of the errexit option,
                      instead of unsetting it  in  the  subshell  environment.   This  option  is
                      enabled when posix mode is enabled.

              interactive_comments
                      If  set, allow a word beginning with # to cause that word and all remaining
                      characters on that line to be ignored in an interactive shell (see COMMENTS
                      above).  This option is enabled by default.

              lastpipe
                      If set, and job control is not active, the shell runs the last command of a
                      pipeline not executed in the background in the current shell environment.

              lithist If set, and the cmdhist option is enabled, multi-line commands are saved to
                      the  history  with embedded newlines rather than using semicolon separators
                      where possible.

              localvar_inherit
                      If set, local variables inherit the value and attributes of a  variable  of
                      the  same  name  that  exists  at  a previous scope before any new value is
                      assigned.  The nameref attribute is not inherited.

              localvar_unset
                      If set, calling unset on local variables in previous function scopes  marks
                      them  so  subsequent  lookups  find them unset until that function returns.
                      This is identical to the behavior  of  unsetting  local  variables  at  the
                      current function scope.

              login_shell
                      The  shell  sets  this  option  if  it  is  started  as  a login shell (see
                      INVOCATION above).  The value may not be changed.

              mailwarn
                      If set, and a file that bash is checking for mail has been  accessed  since
                      the  last  time it was checked, the message ``The mail in mailfile has been
                      read'' is displayed.

              no_empty_cmd_completion
                      If set, and readline is being used, bash will not  attempt  to  search  the
                      PATH  for  possible  completions  when  completion is attempted on an empty
                      line.

              nocaseglob
                      If  set,  bash  matches  filenames  in  a  case-insensitive  fashion   when
                      performing pathname expansion (see Pathname Expansion above).

              nocasematch
                      If set, bash matches patterns in a case-insensitive fashion when performing
                      matching while executing case or [[ conditional commands,  when  performing
                      pattern   substitution   word   expansions,   or  when  filtering  possible
                      completions as part of programmable completion.

              noexpand_translation
                      If set, bash encloses the translated results of $"..."  quoting  in  single
                      quotes instead of double quotes.  If the string is not translated, this has
                      no effect.

              nullglob
                      If set, bash allows patterns which match no files (see  Pathname  Expansion
                      above) to expand to a null string, rather than themselves.

              patsub_replacement
                      If  set, bash expands occurrences of & in the replacement string of pattern
                      substitution to the  text  matched  by  the  pattern,  as  described  under
                      Parameter Expansion above.  This option is enabled by default.

              progcomp
                      If set, the programmable completion facilities (see Programmable Completion
                      above) are enabled.  This option is enabled by default.

              progcomp_alias
                      If set, and programmable completion is enabled, bash treats a command  name
                      that  doesn't  have  any completions as a possible alias and attempts alias
                      expansion. If it has an alias, bash attempts programmable completion  using
                      the command word resulting from the expanded alias.

              promptvars
                      If  set,  prompt strings undergo parameter expansion, command substitution,
                      arithmetic expansion, and quote removal after being expanded  as  described
                      in PROMPTING above.  This option is enabled by default.

              restricted_shell
                      The  shell  sets  this  option  if  it  is  started in restricted mode (see
                      RESTRICTED SHELL below).  The value may not be changed.  This is not  reset
                      when the startup files are executed, allowing the startup files to discover
                      whether or not a shell is restricted.

              shift_verbose
                      If set, the shift builtin prints an error  message  when  the  shift  count
                      exceeds the number of positional parameters.

              sourcepath
                      If set, the . (source) builtin uses the value of PATH to find the directory
                      containing the file supplied as an argument.  This  option  is  enabled  by
                      default.

              varredir_close
                      If  set, the shell automatically closes file descriptors assigned using the
                      {varname} redirection syntax (see REDIRECTION  above)  instead  of  leaving
                      them open when the command completes.

              xpg_echo
                      If set, the echo builtin expands backslash-escape sequences by default.

       suspend [-f]
              Suspend  the  execution  of this shell until it receives a SIGCONT signal.  A login
              shell, or a shell without job control enabled, cannot be suspended; the  -f  option
              can  be  used  to  override  this and force the suspension.  The return status is 0
              unless the shell is a login shell or job control is  not  enabled  and  -f  is  not
              supplied.

       test expr
       [ expr ]
              Return  a  status  of  0  (true)  or  1  (false) depending on the evaluation of the
              conditional expression  expr.   Each  operator  and  operand  must  be  a  separate
              argument.   Expressions  are  composed  of  the  primaries  described  above  under
              CONDITIONAL EXPRESSIONS.  test does not accept any options, nor does it accept  and
              ignore an argument of -- as signifying the end of options.

              Expressions  may  be  combined  using the following operators, listed in decreasing
              order of precedence.  The evaluation depends on the number of arguments; see below.
              Operator precedence is used when there are five or more arguments.
              ! expr True if expr is false.
              ( expr )
                     Returns  the  value  of  expr.   This  may  be  used  to override the normal
                     precedence of operators.
              expr1 -a expr2
                     True if both expr1 and expr2 are true.
              expr1 -o expr2
                     True if either expr1 or expr2 is true.

              test and [ evaluate conditional expressions using a  set  of  rules  based  on  the
              number of arguments.

              0 arguments
                     The expression is false.
              1 argument
                     The expression is true if and only if the argument is not null.
              2 arguments
                     If the first argument is !, the expression is true if and only if the second
                     argument is null.  If the first argument is one  of  the  unary  conditional
                     operators listed above under CONDITIONAL EXPRESSIONS, the expression is true
                     if the unary test is true.  If the first  argument  is  not  a  valid  unary
                     conditional operator, the expression is false.
              3 arguments
                     The  following  conditions  are  applied in the order listed.  If the second
                     argument is one of the  binary  conditional  operators  listed  above  under
                     CONDITIONAL  EXPRESSIONS,  the result of the expression is the result of the
                     binary test using the first and third arguments as operands.  The -a and  -o
                     operators  are  considered  binary operators when there are three arguments.
                     If the first argument is !, the value is the negation  of  the  two-argument
                     test using the second and third arguments.  If the first argument is exactly
                     ( and the third argument is exactly ), the result is the  one-argument  test
                     of the second argument.  Otherwise, the expression is false.
              4 arguments
                     The  following  conditions  are  applied  in the order listed.  If the first
                     argument is !, the result is the negation of the  three-argument  expression
                     composed of the remaining arguments.  the two-argument test using the second
                     and third arguments.  If the first argument is  exactly  (  and  the  fourth
                     argument is exactly ), the result is the two-argument test of the second and
                     third  arguments.   Otherwise,  the  expression  is  parsed  and   evaluated
                     according to precedence using the rules listed above.
              5 or more arguments
                     The  expression  is  parsed  and evaluated according to precedence using the
                     rules listed above.

              When used with test or [, the < and > operators sort lexicographically using  ASCII
              ordering.

       times  Print  the  accumulated  user  and system times for the shell and for processes run
              from the shell.  The return status is 0.

       trap [-lp] [[arg] sigspec ...]
              The command arg is to be read  and  executed  when  the  shell  receives  signal(s)
              sigspec.   If  arg  is  absent (and there is a single sigspec) or -, each specified
              signal is reset to its original disposition (the value it had upon entrance to  the
              shell).   If arg is the null string the signal specified by each sigspec is ignored
              by the shell and by the commands it invokes.  If arg is not present and -p has been
              supplied, then the trap commands associated with each sigspec are displayed.  If no
              arguments are supplied or if only -p is given, trap prints  the  list  of  commands
              associated  with  each  signal.   The -l option causes the shell to print a list of
              signal names and their corresponding numbers.  Each sigspec is either a signal name
              defined  in  <signal.h>, or a signal number.  Signal names are case insensitive and
              the SIG prefix is optional.

              If a sigspec is EXIT (0) the command arg is executed on exit from the shell.  If  a
              sigspec  is  DEBUG,  the  command  arg is executed before every simple command, for
              command, case command, select command, every arithmetic for command, and before the
              first command executes in a shell function (see SHELL GRAMMAR above).  Refer to the
              description of the extdebug option to the shopt builtin for details of  its  effect
              on the DEBUG trap.  If a sigspec is RETURN, the command arg is executed each time a
              shell function or a  script  executed  with  the  .  or  source  builtins  finishes
              executing.

              If  a  sigspec  is  ERR, the command arg is executed whenever a pipeline (which may
              consist of a single simple command), a  list,  or  a  compound  command  returns  a
              non-zero  exit  status,  subject  to the following conditions.  The ERR trap is not
              executed if the failed command is part of the command list immediately following  a
              while  or  until  keyword,  part  of the test in an if statement, part of a command
              executed in a && or || list except the command following the final &&  or  ||,  any
              command  in  a  pipeline  but  the  last, or if the command's return value is being
              inverted using !.  These are the same conditions obeyed by the errexit (-e) option.

              Signals ignored upon entry to the  shell  cannot  be  trapped  or  reset.   Trapped
              signals that are not being ignored are reset to their original values in a subshell
              or subshell environment when one is created.  The return status  is  false  if  any
              sigspec is invalid; otherwise trap returns true.

       type [-aftpP] name [name ...]
              With  no  options, indicate how each name would be interpreted if used as a command
              name.  If the -t option is used, type prints  a  string  which  is  one  of  alias,
              keyword,  function,  builtin,  or  file  if  name is an alias, shell reserved word,
              function, builtin, or disk file, respectively.  If the  name  is  not  found,  then
              nothing  is  printed, and an exit status of false is returned.  If the -p option is
              used, type either returns the name of the disk file that would be executed if  name
              were  specified  as a command name, or nothing if ``type -t name'' would not return
              file.  The -P option forces a PATH search for each name, even if ``type  -t  name''
              would  not  return file.  If a command is hashed, -p and -P print the hashed value,
              which is not necessarily the file that appears first in PATH.  If the -a option  is
              used,  type  prints  all of the places that contain an executable named name.  This
              includes aliases and functions, if and only if the -p option is not also used.  The
              table  of hashed commands is not consulted when using -a.  The -f option suppresses
              shell function lookup, as with the command builtin.  type returns true  if  all  of
              the arguments are found, false if any are not found.

       ulimit [-HS] -a
       ulimit [-HS] [-bcdefiklmnpqrstuvxPRT [limit]]
              Provides control over the resources available to the shell and to processes started
              by it, on systems that allow such control.  The -H and -S options specify that  the
              hard or soft limit is set for the given resource.  A hard limit cannot be increased
              by a non-root user once it is set; a soft limit may be increased up to the value of
              the  hard  limit.  If neither -H nor -S is specified, both the soft and hard limits
              are set.  The value of limit can be a number in the unit specified for the resource
              or  one of the special values hard, soft, or unlimited, which stand for the current
              hard limit, the current soft limit,  and  no  limit,  respectively.   If  limit  is
              omitted, the current value of the soft limit of the resource is printed, unless the
              -H option is given.  When more than one resource is specified, the limit  name  and
              unit,  if appropriate, are printed before the value.  Other options are interpreted
              as follows:
              -a     All current limits are reported; no limits are set
              -b     The maximum socket buffer size
              -c     The maximum size of core files created
              -d     The maximum size of a process's data segment
              -e     The maximum scheduling priority ("nice")
              -f     The maximum size of files written by the shell and its children
              -i     The maximum number of pending signals
              -k     The maximum number of kqueues that may be allocated
              -l     The maximum size that may be locked into memory
              -m     The maximum resident set size (many systems do not honor this limit)
              -n     The maximum number of open file descriptors (most systems do not allow  this
                     value to be set)
              -p     The pipe size in 512-byte blocks (this may not be set)
              -q     The maximum number of bytes in POSIX message queues
              -r     The maximum real-time scheduling priority
              -s     The maximum stack size
              -t     The maximum amount of cpu time in seconds
              -u     The maximum number of processes available to a single user
              -v     The  maximum  amount  of  virtual memory available to the shell and, on some
                     systems, to its children
              -x     The maximum number of file locks
              -P     The maximum number of pseudoterminals
              -R     The  maximum  time  a  real-time  process  can  run  before   blocking,   in
                     microseconds
              -T     The maximum number of threads

              If  limit  is  given,  and the -a option is not used, limit is the new value of the
              specified resource.  If no option is given, then -f  is  assumed.   Values  are  in
              1024-byte  increments,  except  for  -t,  which  is  in  seconds;  -R,  which is in
              microseconds; -p, which is in units of 512-byte blocks; -P, -T, -b, -k, -n, and -u,
              which  are  unscaled  values;  and,  when  in  posix  mode, -c and -f, which are in
              512-byte increments.  The return status is 0 unless an invalid option  or  argument
              is supplied, or an error occurs while setting a new limit.

       umask [-p] [-S] [mode]
              The  user  file-creation  mask  is set to mode.  If mode begins with a digit, it is
              interpreted as an octal number; otherwise it is interpreted as a symbolic mode mask
              similar to that accepted by chmod(1).  If mode is omitted, the current value of the
              mask is printed.  The -S option causes the mask to be printed in symbolic form; the
              default  output  is  an  octal  number.   If the -p option is supplied, and mode is
              omitted, the output is in a form that may be reused as input.  The return status is
              0  if  the  mode  was successfully changed or if no mode argument was supplied, and
              false otherwise.

       unalias [-a] [name ...]
              Remove each name from the list of defined aliases.  If -a is  supplied,  all  alias
              definitions  are removed.  The return value is true unless a supplied name is not a
              defined alias.

       unset [-fv] [-n] [name ...]
              For each name, remove the corresponding variable or function.  If the -v option  is
              given,  each  name refers to a shell variable, and that variable is removed.  Read-
              only variables may not be unset.  If -f is specified, each name refers to  a  shell
              function,  and  the  function definition is removed.  If the -n option is supplied,
              and name is a variable with the nameref attribute, name will be unset  rather  than
              the  variable it references.  -n has no effect if the -f option is supplied.  If no
              options are supplied, each name refers to a variable; if there is  no  variable  by
              that  name,  a  function  with that name, if any, is unset.  Each unset variable or
              function is removed from the environment passed to subsequent commands.  If any  of
              BASH_ALIASES,   BASH_ARGV0,   BASH_CMDS,   BASH_COMMAND,   BASH_SUBSHELL,  BASHPID,
              COMP_WORDBREAKS, DIRSTACK, EPOCHREALTIME, EPOCHSECONDS, FUNCNAME, GROUPS,  HISTCMD,
              LINENO,  RANDOM, SECONDS, or SRANDOM are unset, they lose their special properties,
              even if they are subsequently reset.  The exit status is  true  unless  a  name  is
              readonly or may not be unset.

       wait [-fn] [-p varname] [id ...]
              Wait  for  each specified child process and return its termination status.  Each id
              may be a process ID or a job specification; if a job spec is given,  all  processes
              in  that  job's  pipeline  are  waited for.  If id is not given, wait waits for all
              running background jobs and the last-executed process substitution, if its  process
              id is the same as $!, and the return status is zero.  If the -n option is supplied,
              wait waits for a single job from the list of ids or, if no ids  are  supplied,  any
              job, to complete and returns its exit status.  If none of the supplied arguments is
              a child of the shell, or if  no  arguments  are  supplied  and  the  shell  has  no
              unwaited-for  children,  the exit status is 127.  If the -p option is supplied, the
              process or job identifier of the job for which  the  exit  status  is  returned  is
              assigned  to  the variable varname named by the option argument.  The variable will
              be unset initially, before any assignment.  This is useful only when the -n  option
              is  supplied.  Supplying the -f option, when job control is enabled, forces wait to
              wait for id to terminate before returning its status, instead of returning when  it
              changes  status.   If id specifies a non-existent process or job, the return status
              is 127.  If wait is interrupted by a signal, the return status will be greater than
              128,  as  described  under SIGNALS above.  Otherwise, the return status is the exit
              status of the last process or job waited for.

SHELL COMPATIBILITY MODE

       Bash-4.0 introduced the concept of a shell compatibility level,  specified  as  a  set  of
       options  to the shopt builtin ( compat31, compat32, compat40, compat41, and so on).  There
       is only one current compatibility  level  --  each  option  is  mutually  exclusive.   The
       compatibility  level  is intended to allow users to select behavior from previous versions
       that is incompatible with newer  versions  while  they  migrate  scripts  to  use  current
       features and behavior. It's intended to be a temporary solution.

       This  section  does  not mention behavior that is standard for a particular version (e.g.,
       setting compat32 means that quoting the rhs of the regexp matching operator quotes special
       regexp  characters  in  the  word,  which  is  default behavior in bash-3.2 and subsequent
       versions).

       If a user enables, say, compat32, it may affect the behavior of other compatibility levels
       up  to and including the current compatibility level.  The idea is that each compatibility
       level controls behavior that changed in that version of bash, but that behavior  may  have
       been  present  in  earlier  versions.   For  instance,  the  change  to  use  locale-based
       comparisons with the [[ command came in bash-4.1, and earlier  versions  used  ASCII-based
       comparisons,  so  enabling  compat32  will  enable  ASCII-based comparisons as well.  That
       granularity may not be sufficient for all uses,  and  as  a  result  users  should  employ
       compatibility  levels  carefully.  Read the documentation for a particular feature to find
       out the current behavior.

       Bash-4.3 introduced a new  shell  variable:  BASH_COMPAT.   The  value  assigned  to  this
       variable  (a  decimal version number like 4.2, or an integer corresponding to the compatNN
       option, like 42) determines the compatibility level.

       Starting  with  bash-4.4,  Bash  has  begun  deprecating   older   compatibility   levels.
       Eventually, the options will be removed in favor of BASH_COMPAT.

       Bash-5.0  is  the final version for which there will be an individual shopt option for the
       previous version. Users should use BASH_COMPAT on bash-5.0 and later versions.

       The following table describes the behavior changes controlled by each compatibility  level
       setting.   The compatNN tag is used as shorthand for setting the compatibility level to NN
       using one of the following mechanisms.  For versions prior to bash-5.0, the  compatibility
       level  may  be  set using the corresponding compatNN shopt option.  For bash-4.3 and later
       versions, the BASH_COMPAT variable is preferred, and it is required for bash-5.1 and later
       versions.

       compat31
              •      quoting  the  rhs  of  the [[ command's regexp matching operator (=~) has no
                     special effect

       compat32
              •      interrupting a command list such as "a ; b ; c" causes the execution of  the
                     next  command in the list (in bash-4.0 and later versions, the shell acts as
                     if it received the interrupt, so interrupting one command in a  list  aborts
                     the execution of the entire list)

       compat40
              •      the  <  and > operators to the [[ command do not consider the current locale
                     when comparing strings; they use ASCII ordering.   Bash  versions  prior  to
                     bash-4.1  use  ASCII  collation  and  strcmp(3);  bash-4.1 and later use the
                     current locale's collation sequence and strcoll(3).

       compat41
              •      in posix mode, time may be followed by options and still be recognized as  a
                     reserved word (this is POSIX interpretation 267)
              •      in  posix  mode,  the  parser  requires that an even number of single quotes
                     occur in the word portion of a double-quoted parameter expansion and  treats
                     them  specially,  so that characters within the single quotes are considered
                     quoted (this is POSIX interpretation 221)

       compat42
              •      the replacement  string  in  double-quoted  pattern  substitution  does  not
                     undergo quote removal, as it does in versions after bash-4.2
              •      in  posix mode, single quotes are considered special when expanding the word
                     portion of a double-quoted parameter expansion and can be used  to  quote  a
                     closing   brace   or   other  special  character  (this  is  part  of  POSIX
                     interpretation 221); in later versions, single quotes are not special within
                     double-quoted word expansions

       compat43
              •      the  shell  does  not print a warning message if an attempt is made to use a
                     quoted compound assignment as an  argument  to  declare  (e.g.,  declare  -a
                     foo='(1 2)'). Later versions warn that this usage is deprecated
              •      word expansion errors are considered non-fatal errors that cause the current
                     command to fail, even in posix mode (the default behavior is  to  make  them
                     fatal errors that cause the shell to exit)
              •      when  executing  a shell function, the loop state (while/until/etc.)  is not
                     reset, so break or continue in that function will break or continue loops in
                     the calling context. Bash-4.4 and later reset the loop state to prevent this

       compat44
              •      the  shell  sets  up  the values used by BASH_ARGV and BASH_ARGC so they can
                     expand to the shell's positional parameters even if extended debugging  mode
                     is not enabled
              •      a subshell inherits loops from its parent context, so break or continue will
                     cause the subshell to exit.  Bash-5.0 and later  reset  the  loop  state  to
                     prevent the exit
              •      variable  assignments  preceding  builtins like export and readonly that set
                     attributes continue to affect variables with the same name  in  the  calling
                     environment even if the shell is not in posix mode

       compat50
              •      Bash-5.1  changed  the  way  $RANDOM is generated to introduce slightly more
                     randomness. If the shell compatibility level is  set  to  50  or  lower,  it
                     reverts  to  the  method from bash-5.0 and previous versions, so seeding the
                     random number generator by assigning a value to RANDOM will produce the same
                     sequence as in bash-5.0
              •      If  the command hash table is empty, bash versions prior to bash-5.1 printed
                     an informational message to that effect, even when producing output that can
                     be  reused  as input. Bash-5.1 suppresses that message when the -l option is
                     supplied.

       compat51
              •      The unset builtin  treats  attempts  to  unset  array  subscripts  @  and  *
                     differently  depending  on  whether the array is indexed or associative, and
                     differently than in previous versions.

RESTRICTED SHELL

       If bash is started with the name rbash, or the -r option is supplied  at  invocation,  the
       shell  becomes  restricted.   A  restricted  shell  is  used to set up an environment more
       controlled than the standard shell.  It behaves identically to  bash  with  the  exception
       that the following are disallowed or not performed:

       •      changing directories with cd

       •      setting or unsetting the values of SHELL, PATH, HISTFILE, ENV, or BASH_ENV

       •      specifying command names containing /

       •      specifying a filename containing a / as an argument to the .  builtin command

       •      specifying  a  filename  containing  a  slash as an argument to the history builtin
              command

       •      specifying a filename containing a slash as an argument to the  -p  option  to  the
              hash builtin command

       •      importing function definitions from the shell environment at startup

       •      parsing the value of SHELLOPTS from the shell environment at startup

       •      redirecting output using the >, >|, <>, >&, &>, and >> redirection operators

       •      using the exec builtin command to replace the shell with another command

       •      adding  or  deleting  builtin  commands  with  the  -f and -d options to the enable
              builtin command

       •      using the enable builtin command to enable disabled shell builtins

       •      specifying the -p option to the command builtin command

       •      turning off restricted mode with set +r or shopt -u restricted_shell.

       These restrictions are enforced after any startup files are read.

       When a command that is found to be a shell  script  is  executed  (see  COMMAND  EXECUTION
       above), rbash turns off any restrictions in the shell spawned to execute the script.

SEE ALSO

       Bash Reference Manual, Brian Fox and Chet Ramey
       The Gnu Readline Library, Brian Fox and Chet Ramey
       The Gnu History Library, Brian Fox and Chet Ramey
       Portable Operating System Interface (POSIX) Part 2: Shell and Utilities, IEEE --
              http://pubs.opengroup.org/onlinepubs/9699919799/
       http://tiswww.case.edu/~chet/bash/POSIX -- a description of posix mode
       sh(1), ksh(1), csh(1)
       emacs(1), vi(1)
       readline(3)

FILES

       /bin/bash
              The bash executable
       /etc/profile
              The systemwide initialization file, executed for login shells
       /etc/bash.bashrc
              The systemwide per-interactive-shell startup file
       /etc/bash.bash.logout
              The systemwide login shell cleanup file, executed when a login shell exits
       ~/.bash_profile
              The personal initialization file, executed for login shells
       ~/.bashrc
              The individual per-interactive-shell startup file
       ~/.bash_logout
              The individual login shell cleanup file, executed when a login shell exits
       ~/.bash_history
              The default value of HISTFILE, the file in which bash saves the command history
       ~/.inputrc
              Individual readline initialization file

AUTHORS

       Brian Fox, Free Software Foundation
       bfox@gnu.org

       Chet Ramey, Case Western Reserve University
       chet.ramey@case.edu

BUG REPORTS

       If  you find a bug in bash, you should report it.  But first, you should make sure that it
       really is a bug, and that it appears in the latest version of bash.  The latest version is
       always          available         from         ftp://ftp.gnu.org/pub/gnu/bash/         and
       http://git.savannah.gnu.org/cgit/bash.git/snapshot/bash-master.tar.gz.

       Once you have determined that a bug actually exists, use the bashbug command to  submit  a
       bug  report.  If you have a fix, you are encouraged to mail that as well!  Suggestions and
       `philosophical' bug reports may be mailed to bug-bash@gnu.org  or  posted  to  the  Usenet
       newsgroup gnu.bash.bug.

       ALL bug reports should include:

       The version number of bash
       The hardware and operating system
       The compiler used to compile
       A description of the bug behaviour
       A short script or `recipe' which exercises the bug

       bashbug  inserts  the  first  three  items automatically into the template it provides for
       filing a bug report.

       Comments  and  bug  reports  concerning  this  manual   page   should   be   directed   to
       chet.ramey@case.edu.

BUGS

       It's too big and too slow.

       There  are  some  subtle  differences  between bash and traditional versions of sh, mostly
       because of the POSIX specification.

       Aliases are confusing in some uses.

       Shell builtin commands and functions are not stoppable/restartable.

       Compound commands and command sequences of the form `a ; b ; c' are not handled gracefully
       when  process  suspension  is attempted.  When a process is stopped, the shell immediately
       executes the next command in the sequence.  It suffices to place the sequence of  commands
       between parentheses to force it into a subshell, which may be stopped as a unit.

       Array variables may not (yet) be exported.

       There may be only one active coprocess at a time.