Provided by: bash_5.0-6ubuntu1.2_amd64 bug

NAME

       bash - GNU Bourne-Again SHell

SYNOPSIS

       bash [options] [command_string | file]

COPYRIGHT

       Bash is Copyright (C) 1989-2018 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 simple command (see SHELL GRAMMAR below) or the
       third word of a case or for command:

       ! 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  (as 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.   Substrings  matched  by  parenthesized
       subexpressions  within  the regular expression are saved in the array variable BASH_REMATCH.  The element
       of BASH_REMATCH with index 0 is the portion of the string matching the entire  regular  expression.   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.  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:

       name () compound-command [redirection]
       function name [()] compound-command [redirection]
              This defines a function named name.  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 name is specified as the name of a simple
              command.  When in posix mode, name may not be the name of one of the POSIX special builtins.   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.  If the current locale is C or POSIX, 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.
       _      At  shell  startup,  set  to  the absolute 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.

   Shell Variables
       The following variables are set by the shell:

       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.
       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.  This variable is read-only.
       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.
       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.  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, a random integer between 0 and 32767  is  generated.   The
              sequence of random numbers may be initialized by assigning a value to RANDOM.  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_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.  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.
       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  the  description  of  the  shopt
              builtin  below  under SHELL BUILTIN COMMANDS 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
              compatibility  levels  correspond  to  the  compatibility  options  accepted  by the shopt builtin
              described below (for example, compat42 means that 4.2 and  42  are  valid  values).   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    Similar to BASH_ENV; used when the 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 set, the value is executed as a command prior to issuing each primary prompt.
       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  The  full  pathname  to the shell is kept in this environment variable.  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
       is  of  the form [subscript]=string.  Indexed array assignments do not require anything but string.  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 subscript is required.

       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:

              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.
              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, 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.

       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, 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 abd [ 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.

       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 ce job.  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 will force 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).

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.  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

       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, the user is asked whether or not he 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 (Off)
              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.
       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-screen (C-l)
              Clear the screen 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.
       ^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 word matched by the most recent `?string?' search.
       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  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 `:'.

       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.
       s/old/new/
              Substitute  new  for  the first occurrence of old in the event line.  Any delimiter can be used 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.
       &      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' 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 variable to the current location of the insertion point.   If
                     the executed command changes the value of READLINE_LINE or READLINE_POINT, 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 inital 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  inital  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 [-aAfFgilnrtux] [-p] [name[=value] ...]
       typeset [-aAfFgilnrtux] [-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
              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).  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 [args]
              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 given in args,
              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.   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.

              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 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
                      If set, bash changes its behavior to that of version 3.1 with respect to quoted  arguments
                      to  the  [[  conditional  command's =~ operator and locale-specific string comparison when
                      using the [[ conditional command's < and > operators.  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).
              compat32
                      If  set,  bash changes its behavior to that of version 3.2 with respect to locale-specific
                      string comparison when using the [[ conditional command's < and > operators (see  previous
                      item)  and  the  effect  of  interrupting  a  command list.  Bash versions 3.2 and earlier
                      continue with the next command in the list after one terminates due to an interrupt.
              compat40
                      If set, bash changes its behavior to that of version 4.0 with respect  to  locale-specific
                      string  comparison  when  using  the  [[  conditional  command's  <  and  > operators (see
                      description of compat31) and the effect of interrupting a command list.  Bash versions 4.0
                      and later interrupt the list as if the shell received  the  interrupt;  previous  versions
                      continue with the next command in the list.
              compat41
                      If  set,  bash,  when  in  posix  mode, treats a single quote in a double-quoted parameter
                      expansion as a special character.  The single quotes must match (an even number)  and  the
                      characters between the single quotes are considered quoted.  This is the behavior of posix
                      mode through version 4.1.  The default bash behavior remains as in previous versions.
              compat42
                      If  set,  bash  does  not  process the replacement string in the pattern substitution word
                      expansion using quote removal.
              compat43
                      If set, bash does not print a warning message if an  attempt  is  made  to  use  a  quoted
                      compound array assignment as an argument to declare, makes word expansion errors non-fatal
                      errors  that cause the current command to fail (the default behavior is to make them fatal
                      errors that cause the shell to exit), and does not reset  the  loop  state  when  a  shell
                      function is executed (this allows break or continue in a shell function to affect loops in
                      the caller's context).
              compat44
                      If  set,  bash  saves the positional parameters to BASH_ARGV and BASH_ARGC before they are
                      used, regardless of whether or not extended debugging mode is enabled.
              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, 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 [-HSabcdefiklmnpqrstuvxPT [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 are printed before the value.  Other
              options are interpreted as follows:
              -a     All current limits are reported
              -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
              -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; -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, any function with that name is unset.  Each unset variable or function is removed  from
              the  environment  passed  to  subsequent  commands.   If  any of COMP_WORDBREAKS, RANDOM, SECONDS,
              LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK 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] [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, all currently active child processes are  waited  for,  and  the  return
              status is zero.  If the -n option is supplied, wait waits for any job to terminate and returns its
              exit  status.   If  the  -f  option  is  supplied,  and  job control is enabled, wait forces 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.

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, 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 -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.

GNU Bash 5.0                                     2018 December 7                                         BASH(1)