Provided by: bash_5.1-3ubuntu2_amd64 bug

NAME

       bash - GNU Bourne-Again SHell

SYNOPSIS

       bash [options] [command_string | file]

COPYRIGHT

       Bash is Copyright (C) 1989-2020 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 remote shell  daemon,  usually  rshd,  or  the
       secure  shell  daemon  sshd.  If bash determines it is being run in this fashion, it reads
       and executes commands from ~/.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

   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]] [ ! ] command [ [||&] command2 ... ]

       The standard output of command is connected via a pipe to the standard input of  command2.
       This  connection  is  performed  before  any  redirections  specified  by the command (see
       REDIRECTION below).  If |& is used, command'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 the command.

       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 pipeline is executed as a separate process (i.e., in a  subshell).   See
       COMMAND  EXECUTION  ENVIRONMENT  for  a  description  of  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.

   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  environment (see COMMAND EXECUTION ENVIRONMENT
              below).   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.  This is exactly equivalent to let "expression".

       [[ 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.   Word splitting and pathname expansion are not performed
              on the words between the  [[  and  ]];  tilde  expansion,  parameter  and  variable
              expansion,  arithmetic  expansion,  command substitution, process substitution, and
              quote removal are performed.  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.  Any part of the pattern
       may be quoted to force the quoted portion to be matched as a string.  Bracket  expressions
       in  regular  expressions  must  be treated carefully, since normal quoting characters lose
       their meanings between brackets.  If the pattern is stored in a  shell  variable,  quoting
       the variable expansion forces the entire pattern to be matched as a string.

       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.

       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.  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).
              The  PS3  prompt is then displayed and a line read 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 command  completes.   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, and process substitution.
              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 format for a coprocess is:

              coproc [NAME] command [redirections]

       This creates a coprocess named NAME.  If NAME is not supplied, the default name is COPROC.
       NAME must not be supplied if command is a simple command (see  above);  otherwise,  it  is
       interpreted  as 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, with one exception: If  the  function
              reserved  word  is  used,  but  the  parentheses  are  not supplied, the braces are
              required.  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).

       Words of the form $'string' are treated specially.   The  word  expands  to  string,  with
       backslash-escaped  characters  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
       message catalog lookup  and  translation,  using  the  LC_MESSAGES  and  TEXTDOMAIN  shell
       variables.   If  the  current  locale  is  C  or  POSIX,  or  if there are no translations
       available, the dollar sign is ignored.  If the string  is  translated  and  replaced,  the
       replacement is double-quoted.

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 $((...)) expansion is not
       used (see Arithmetic  Expansion  below).   Word  splitting  is  not  performed,  with  the
       exception  of "$@" as explained below under Special Parameters.  Pathname expansion is 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_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,  the  number  of  seconds  since  shell
              invocation is returned.  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 is 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 BSHELLCOMPATIBILITYMODE.   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.

       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, or  unset
       name[subscript], where subscript is * or @, removes the entire array.

       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 characters, 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 characters  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.   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 @, 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 @, 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}
              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.   The  match  is  performed using the rules
              described under Pattern Matching below.  If pattern begins with /, all  matches  of
              pattern  are  replaced with string.  Normally only the first match is replaced.  If
              pattern begins with #, it must match at the beginning  of  the  expanded  value  of
              parameter.   If  pattern  begins  with  %, it must match at the end of the expanded
              value of parameter.  If string is null, matches of pattern are deleted  and  the  /
              following  pattern may be omitted.  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.

              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 is treated as if it were within double quotes, but a  double  quote  inside
       the  parentheses is not treated specially.  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.  The filenames ``.''  and ``..''  must
       always  be  matched  explicitly,  even  if  dotglob  is  set.   In  other cases, 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, 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  is  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, several  extended  pattern
       matching operators are recognized.  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

       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 himself.

       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, a shell function should be used (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.
       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).  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 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.

       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 subshells 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.
       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.  A
       subshell is spawned 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.

       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.

       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.

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 current working directory, with $HOME abbreviated with a tilde (uses the
                     value of the PROMPT_DIRTRIM variable)
              \W     the basename of the current working directory, 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:

       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.
       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.
       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.
       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-bracketed-paste (On)
              When set to On, readline will configure the terminal in a way that will  enable  it
              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
              can prevent pasted characters from being interpreted as editing commands.
       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.
       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.
       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.
       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.
       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.
       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 count 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 count 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.
       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.  The file searched for in PATH need not be executable.  When bash is  not
              in  posix  mode, the current directory is searched 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,  source inherits any trap on DEBUG; if it is not, any
              DEBUG trap string is saved and restored around  the  call  to  source,  and  source
              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  source  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
              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 .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.  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.  Any additional arguments following dir are ignored.
              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.  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.
              -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.  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.  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 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  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.   With no arguments, removes the top
              directory from the stack, and performs a cd 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.  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 popd command is successful, a dirs is performed  as  well,  and  the  return
              status is 0.  popd returns false if an invalid option is encountered, the directory
              stack is empty, a non-existent directory stack entry is specified, or the directory
              change fails.

       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.
              %(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  directories  and returns 0, unless the directory stack is
              empty.  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, making it the new current
                     working directory as if it had been supplied  as  the  argument  to  the  cd
                     builtin.

              If the pushd command is successful, a dirs is performed as well.  If the first form
              is used, pushd returns 0 unless the cd to dir fails.  With the second  form,  pushd
              returns  0  unless  the  directory  stack  is empty, a non-existent directory stack
              element is specified,  or  the  directory  change  to  the  specified  new  current
              directory fails.

       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, 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,  the  name  and  value  of each shell variable are displayed 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.
              -t      Exit after reading and executing one command.
              -u      Treat  unset variables and parameters other than the special parameters "@"
                      and "*" 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
                      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.

              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.

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

              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.

              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 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 and -f is not
              supplied, or if job control is not enabled.

       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
                     If the first argument is !, the result is the negation of the three-argument
                     expression  composed  of the remaining 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.

       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.  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 above).

       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  (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.

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 set +o restricted.

       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
       ~/.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/.

       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.