The Atari Compendium/The Atari Compendium (Toad Computers) (1994).iso/files/prgtools/gnustuff/tos/futils/futils~1/man/manpages.zoo/bash.1

Text File | 1991-11-11 | 120.3 KB | 3,103 lines

BASH(1)                   1991 July 15                    BASH(1)



NAME
     bash - GNU Bourne-Again SHell

SYNOPSIS
     bash [options] [file]

COPYRIGHT
     Copyright (C) 1989, 1991 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 _✓K_✓o_✓r_✓n
     and _✓C shells (ksh and csh).

     Bash is ultimately intended to be a faithful implementation
     of the IEEE Posix Shell and Tools specification (IEEE Work-
     ing Group 1003.2).

OPTIONS
     In addition to the single-character shell options documented
     in the description of the set builtin command, bash inter-
     prets the following flags when it is invoked:

     -c _✓s_✓t_✓r_✓i_✓n_✓g If the -c flag is present, then commands are read
               from _✓s_✓t_✓r_✓i_✓n_✓g.
     -i        If the -i flag is present, the shell is _✓i_✓n_✓t_✓e_✓r_✓a_✓c_✓-
               _✓t_✓i_✓v_✓e.
     -s        If the -s flag 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.
     -         A single - 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 an argument of -.

     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.

     -norc     Do not load the personal initialization file
               ~/._✓b_✓a_✓s_✓h_✓r_✓c if the shell is interactive.  This is
               the default if the shell name is sh.
     -noprofile
               Do not read either /_✓e_✓t_✓c/_✓p_✓r_✓o_✓f_✓i_✓l_✓e or
               ~/._✓b_✓a_✓s_✓h__✓p_✓r_✓o_✓f_✓i_✓l_✓e.  By default, bash normally reads
               these files when it is invoked as a login shell.
     -rcfile _✓f_✓i_✓l_✓e
               Execute commands from _✓f_✓i_✓l_✓e instead of the standard



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               personal initialization file ~/._✓b_✓a_✓s_✓h_✓r_✓c, if the
               shell is interactive.
     -version  Show the version number of this instance of bash
               when starting.
     -quiet    Do not be verbose when starting up (do not show
               the shell version or any other information).
     -login    Make bash act as if it had been invoked by
               login(1).
     -nobraceexpansion
               Do not perform curly brace expansion a la csh.
     -nolineediting
               Do not use the GNU _✓r_✓e_✓a_✓d_✓l_✓i_✓n_✓e library to read com-
               mand lines if interactive.

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 com-
     mands.  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.

DEFINITIONS
     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 _✓w_✓o_✓r_✓d 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>
     control operator
          A _✓t_✓o_✓k_✓e_✓n that performs a control function.  It is one of
          the following symbols:
          || & && ; ;; ( ) | <newline>

RESERVED WORDS
     _✓R_✓e_✓s_✓e_✓r_✓v_✓e_✓d _✓w_✓o_✓r_✓d_✓s 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 com-
     mand:

     ! case  do done elif else esac fi for function if in then
     until while { }

SHELL GRAMMAR




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     Simple Commands

     A _✓s_✓i_✓m_✓p_✓l_✓e _✓c_✓o_✓m_✓m_✓a_✓n_✓d is a sequence of optional variable assign-
     ments followed by _✓b_✓l_✓a_✓n_✓k-separated words and redirections,
     and terminated by a _✓c_✓o_✓n_✓t_✓r_✓o_✓l _✓o_✓p_✓e_✓r_✓a_✓t_✓o_✓r.  The first word speci-
     fies the command to be executed.  The remaining words are
     passed as arguments to the invoked command.

     The return value of a _✓s_✓i_✓m_✓p_✓l_✓e _✓c_✓o_✓m_✓m_✓a_✓n_✓d is its exit status, or
     128+_✓n if the command is terminated by signal _✓n.

     Pipelines

     A _✓p_✓i_✓p_✓e_✓l_✓i_✓n_✓e is a sequence of one or more commands separated
     by the character |.  The format for a pipeline is:

          [ ! ] _✓c_✓o_✓m_✓m_✓a_✓n_✓d [ | _✓c_✓o_✓m_✓m_✓a_✓n_✓d_✓2 ... ]

     The standard output of _✓c_✓o_✓m_✓m_✓a_✓n_✓d is connected to the standard
     input of _✓c_✓o_✓m_✓m_✓a_✓n_✓d_✓2.  This connection is performed before any
     redirections specified by the command (see REDIRECTION
     below).

     If the reserved word ! precedes a pipeline, the exit status
     of that pipeline is the logical NOT of the exit status of
     the last command.  Otherwise, the status of the pipeline is
     the exit status of the last command.  The shell waits for
     all commands in the pipeline to terminate before returning a
     value.

     Each command in a pipeline is executed as a separate process
     (i.e. in a subshell).

     Lists

     A _✓l_✓i_✓s_✓t is a sequence of one or more pipelines separated by
     one of the operators ;, &, &&, or ||, and optionally ter-
     minated by one of ;, &, or <newline>.

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

     If a command is terminated by the control operator &, the
     shell executes the command in the _✓b_✓a_✓c_✓k_✓g_✓r_✓o_✓u_✓n_✓d in a subshell.
     The shell does not wait for the command to finish.  Commands
     separated by a ; are executed sequentially; the shell waits
     for each command to terminate in turn.

     The control operators && and || denote AND lists and OR
     lists, respectively.  An AND list has the form




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          _✓c_✓o_✓m_✓m_✓a_✓n_✓d && _✓c_✓o_✓m_✓m_✓a_✓n_✓d_✓2

     _✓c_✓o_✓m_✓m_✓a_✓n_✓d_✓2 is executed if, and only if, _✓c_✓o_✓m_✓m_✓a_✓n_✓d returns an
     exit status of zero.

     An OR list has the form

          _✓c_✓o_✓m_✓m_✓a_✓n_✓d || _✓c_✓o_✓m_✓m_✓a_✓n_✓d_✓2

     _✓c_✓o_✓m_✓m_✓a_✓n_✓d_✓2 is executed if and only if _✓c_✓o_✓m_✓m_✓a_✓n_✓d returns a non-
     zero exit status.

     Compound Commands

     A _✓c_✓o_✓m_✓p_✓o_✓u_✓n_✓d _✓c_✓o_✓m_✓m_✓a_✓n_✓d is one of the following:

     (_✓l_✓i_✓s_✓t)
          _✓l_✓i_✓s_✓t is executed in a subshell.  Variable assignments
          and builtin commands that affect the shell's environ-
          ment do not remain in effect after the command com-
          pletes.

     { _✓l_✓i_✓s_✓t; }
          _✓l_✓i_✓s_✓t is simply executed in the current shell environ-
          ment.  This is known as a _✓g_✓r_✓o_✓u_✓p _✓c_✓o_✓m_✓m_✓a_✓n_✓d.

     for _✓n_✓a_✓m_✓e [ in _✓w_✓o_✓r_✓d ] do _✓l_✓i_✓s_✓t done
          The list of words following in is expanded, generating
          a list of items.  The variable _✓n_✓a_✓m_✓e is set to each ele-
          ment of this list in turn, and _✓l_✓i_✓s_✓t is executed each
          time.  If the in _✓w_✓o_✓r_✓d is omitted, the for command exe-
          cutes _✓l_✓i_✓s_✓t once for each positional parameter that is
          set (see PARAMETERS below).  The exit status is the
          exit status of the last command, or zero if no commands
          were executed.

     case _✓w_✓o_✓r_✓d in [ _✓p_✓a_✓t_✓t_✓e_✓r_✓n [ | _✓p_✓a_✓t_✓t_✓e_✓r_✓n ] ... ) _✓l_✓i_✓s_✓t ;; ] ... esac
          A case command first expands _✓w_✓o_✓r_✓d, and tries to match
          it against each _✓p_✓a_✓t_✓t_✓e_✓r_✓n in turn.  When a match is
          found, the corresponding _✓l_✓i_✓s_✓t is executed.  After the
          first match, no subsequent matches are attempted.  The
          exit status is zero if no patterns are matches.  Other-
          wise, it is the exit status of the last command exe-
          cuted in _✓l_✓i_✓s_✓t.

     if _✓l_✓i_✓s_✓t then _✓l_✓i_✓s_✓t [ elif _✓l_✓i_✓s_✓t then _✓l_✓i_✓s_✓t ] ... [ else _✓l_✓i_✓s_✓t ] fi
          The if _✓l_✓i_✓s_✓t is executed.  If its exit status is zero,
          the then _✓l_✓i_✓s_✓t is executed.  Otherwise, each elif _✓l_✓i_✓s_✓t
          is executed in turn, and if its exit status is zero,
          the corresponding then _✓l_✓i_✓s_✓t is executed and the command
          completes.  Otherwise, the else _✓l_✓i_✓s_✓t is executed, if
          present.  The exit status is the exit status of the



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          last command executed, or zero if no condition tested
          true.

     while _✓l_✓i_✓s_✓t do _✓l_✓i_✓s_✓t done
     until _✓l_✓i_✓s_✓t do _✓l_✓i_✓s_✓t done
          The while command continuously executes the do _✓l_✓i_✓s_✓t as
          long as the last command in _✓l_✓i_✓s_✓t returns an exit status
          of zero.  The until command is identical to the while
          command, except that the test is negated; the do _✓l_✓i_✓s_✓t
          is executed as long as the last command in _✓l_✓i_✓s_✓t returns
          a non-zero exit status.  The exit status of the while
          and until commands is the exit status of the last do
          _✓l_✓i_✓s_✓t command executed, or zero if none was executed.

     [ function ] _✓n_✓a_✓m_✓e () { _✓l_✓i_✓s_✓t; }
          This defines a function named _✓n_✓a_✓m_✓e.  The _✓b_✓o_✓d_✓y of the
          function is the _✓l_✓i_✓s_✓t of commands between { and }.  This
          list is executed whenever _✓n_✓a_✓m_✓e is specified as the name
          of a simple command.  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, a word beginning with # causes
     that word and all remaining characters on that line to be
     ignored.

QUOTING
     _✓Q_✓u_✓o_✓t_✓i_✓n_✓g 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 _✓m_✓e_✓t_✓a_✓c_✓h_✓a_✓r_✓a_✓c_✓t_✓e_✓r_✓s listed above under DEFINITIONS
     has special meaning to the shell and must be quoted if they
     are to represent themselves.  There are three quoting
     mechanisms: the escape character, single quotes, and double
     quotes.

     A non-quoted backslash (\) is the _✓e_✓s_✓c_✓a_✓p_✓e _✓c_✓h_✓a_✓r_✓a_✓c_✓t_✓e_✓r.  It
     preserves the literal value of the next character that fol-
     lows, with the exception of <newline>.  If a \<newline> pair
     appears, it is treated as a line continuation (that is, it
     is effectively ignored), if the backslash is non-quoted.

     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.





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     Enclosing characters in double quotes preserves the literal
     value of all characters within the quotes, with the excep-
     tion of $, `, and \.  The characters $ and ` retain their
     special meaning within double quotes.  The backslash retains
     its special meaning only when followed by one of the follow-
     ing characters:  $, `, ", \, or <newline>.  A double quote
     may be quoted within double quotes by preceding it with a
     backslash.

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

PARAMETERS
     A _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r is an entity that stores values, somewhat like a
     variable in a conventional programming language.  It can be
     a _✓n_✓a_✓m_✓e, a number, or one of the special characters listed
     below under Special Parameters.  For the shell's purposes, a
     _✓v_✓a_✓r_✓i_✓a_✓b_✓l_✓e is a parameter denoted by a _✓n_✓a_✓m_✓e.

     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 _✓v_✓a_✓r_✓i_✓a_✓b_✓l_✓e may be assigned to by a statement of the form

          _✓n_✓a_✓m_✓e=[_✓v_✓a_✓l_✓u_✓e]

     If _✓v_✓a_✓l_✓u_✓e is not given, the variable is assigned the null
     string.  All _✓v_✓a_✓l_✓u_✓e_✓s undergo tilde expansion, parameter and
     variable expansion, command substitution, arithmetic expan-
     sion, and quote removal.  If the variable has its -i attri-
     bute set (see declare below in SHELL BUILTIN COMMANDS) then
     _✓v_✓a_✓l_✓u_✓e is subject to arithmetic expansion even if the $[...]
     syntax does not appear.  Word splitting is not performed,
     with the exception of "$@" as explained below under Special
     Parameters.  Pathname expansion is not performed.

     Positional Parameters

     A _✓p_✓o_✓s_✓i_✓t_✓i_✓o_✓n_✓a_✓l _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r is a parameter denoted by one or more
     digits, other than the single digit 0.  Positional parame-
     ters are assigned from the shell's arguments when it is
     invoked, and may be reassigned using the set builtin com-
     mand.  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 EXPAN-
     SION below).





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     Special Parameters

     The shell treats several parameters specially.  These param-
     eters may only be referenced; assignment to them is not
     allowed.
     *    Expands to the positional parameters, starting from
          one.  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
          ``$1_✓c$2_✓c...'', where _✓c is the first character of the
          value of the IFS variable.  If IFS is null or unset,
          the parameters are separated by spaces.
     @    Expands to the positional parameters, starting from
          one.  When the expansion occurs within double quotes,
          each parameter expands as a separate word.  That is, ``
          $@'' is equivalent to ``$1'' ``$2'' ...  When there are
          no positional parameters, ``$@'' and $@ expand to noth-
          ing (i.e. they are removed).
     #    Expands to the number of positional parameters in
          decimal.
     ?    Expands to the 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 flag).
     $    Expands to the process ID of the shell.  In a () sub-
          shell, it expands to the process ID of the current
          shell, not the subshell.
     !    Expands to the process ID of the most recently executed
          background (asynchronous) command.
     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.  Otherwise, it is set to the pathname used to
          invoke bash, as given by argument zero.
     _    Expands to the last argument to the previous command,
          after expansion.  Also set to the full pathname of each
          command executed and placed in the environment exported
          to that command.

     Shell Variables

     The following variables are set by the shell:

     PPID The process ID of the shell's parent.
     PWD  The current working directory as set by the cd command.
     OLDPWD
          The previous working directory as set by the cd com-
          mand.
     REPLY
          Set to the line of input read by the read builtin



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          command when no arguments are supplied.
     UID  Expands to the user ID of the current user.
     EUID Expands to the effective user ID of the current user.
     BASH Expands to the full pathname used to invoke this
          instance of bash.
     BASH_VERSION
          Expands to the version number of this instance of bash.
     SHLVL
          Incremented by one each time an instance of bash is
          started.
     RANDOM
          Each time this parameter is referenced, a random
          integer 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.
     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 subse-
          quent 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.
     LINENO
          Each time this parameter is referenced, the shell sub-
          stitutes 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 meaning-
          ful.  When in a function, the value is not the number
          of the source line that the command appears on (that
          information has been lost by the time the function is
          executed), but is an approximation of the number of
          _✓s_✓i_✓m_✓p_✓l_✓e _✓c_✓o_✓m_✓m_✓a_✓n_✓d_✓s executed in the current function.  If
          LINENO is unset, it loses its special properties, even
          if it is subsequently reset.
     OPTARG
          The value of the last option argument processed by the
          getopts builtin command (see SHELL BUILTIN COMMANDS
          below).
     OPTIND
          The index of the last option processed by the getopts
          builtin command (see SHELL BUILTIN COMMANDS below).

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

     IFS  The _✓I_✓n_✓t_✓e_✓r_✓n_✓a_✓l _✓F_✓i_✓e_✓l_✓d _✓S_✓e_✓p_✓a_✓r_✓a_✓t_✓o_✓r that is used for word
          splitting after expansion and to split lines into words
          with the read builtin command.  The default value is



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          ``<space><tab><newline>''.
     PATH The search path for commands.  It is a colon-separated
          list of directories in which the shell looks for com-
          mands (see COMMAND EXECUTION below).  The default path
          is system-dependent, and is set by the administrator
          who installs bash.  A common value is
          ``.:/usr/gnu/bin:/usr/local/bin:/usr/ucb:/bin:/usr/bin:/etc:/usr/etc''.
          Note that in some circumstances, however, a leading `.'
          in PATH can be a security hazard.
     HOME The home directory of the current user; the default
          argument for the cd builtin command.
     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 com-
          mand.  A sample value is ``.:~:/usr''.
     ENV  If this parameter is set when bash is executing a shell
          script, its value is interpreted as a filename contain-
          ing commands to initialize the shell, as in ._✓b_✓a_✓s_✓h_✓r_✓c.
          The value of ENV is subjected to parameter expansion,
          command substitution, and arithmetic expansion before
          being interpreted as a pathname.  PATH is not used to
          search for the resultant pathname.
     MAIL If this parameter is set to a filename and the MAILPATH
          variable is not set, bash informs the user of the
          arrival of mail in the specified file.
     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 prompting.  If this
          variable is unset, the shell disables mail checking.
     MAILPATH
          A colon-separated list of pathnames to be checked for
          mail. The message to be printed may be specified by
          separating the pathname from the message with a `?'.
          $_ stands for the name of the current mailfile. Exam-
          ple:
          MAILPATH='/usr/spool/mail/bfox?"You have
          mail":~/shell-mail?"$_ has mail!"'
          Bash supplies a default value for this variable, but
          the location of the user mail files that it uses is
          system dependent (e.g. /usr/spool/mail/$USER).
     MAIL_WARNING
          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` _✓m_✓a_✓i_✓l_✓f_✓i_✓l_✓e has been read'' is
          printed.
     PS1  The value of this parameter is expanded (see PROMPTING
          below) and used as the primary prompt string.  The
          default value is ``bash\$ ''.
     PS2  The value of this parameter is expanded like PS1 and
          used as the secondary prompt string.  The default is



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          ``bash> ''.
     PS4  The value of this parameter is expanded like PS1 and
          the value is printed before each command bash displays
          during an execution trace.  The first character of PS4
          is replicated multiple times, as necessary, to indicate
          multiple levels of indirection.  The default is ``+ ''.
     NO_PROMPT_VARS
          If set, the decoded prompt string does not undergo
          further expansion (see PROMPTING below).
     HISTSIZE
          The number of commands to remember in the command his-
          tory (see HISTORY below).
     HISTFILE
          The name of the file in which command history is saved.
          (See HISTORY below.)
     HISTFILESIZE
          The maximum number of lines contained in the history
          file.  When this variable is assigned a value, the his-
          tory file is truncated, if necessary, to contain no
          more than that number of lines.
     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.
     PROMPT_COMMAND
          If set, the value is executed as a command prior to
          issuing each primary prompt.
     IGNOREEOF
     ignoreeof
          Controls the action of the shell on receipt of an EOF
          character as the sole input.  If set, the value is the
          number of consecutive EOF characters typed 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.  This is only in effect for
          interactive shells.
     HOSTTYPE
          Automatically set to a string that uniquely describes
          the type of machine on which bash is executing.  The
          default is system-dependent.
     TMOUT
          If set to a value greater than zero, the value is
          interpreted as the number of seconds to wait for input
          after issuing the primary prompt.  Bash terminates
          after waiting for that number of seconds if input does
          not arrive.
     FCEDIT
          The default editor for the fc builtin command.
     FIGNORE



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          A colon-separated list of suffixes to ignore when per-
          forming 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:~''.
     notify
          If set, bash reports terminated background jobs immedi-
          ately, rather than waiting until before printing the
          next primary prompt.
     history_control
          If set to a value of _✓i_✓g_✓n_✓o_✓r_✓e_✓s_✓p_✓a_✓c_✓e, it means don't enter
          lines which begin with a <space> on the history list.
          If set to a value of _✓i_✓g_✓n_✓o_✓r_✓e_✓d_✓u_✓p_✓s, it means don't enter
          lines which match the last entered line.  If unset, or
          if set to any other value than those above, all lines
          read by the parser are saved on the history list.
     glob_dot_filenames
          If set, bash includes filenames beginning with a `.' in
          the results of pathname expansion.
     allow_null_glob_expansion
          If set, bash allows pathname patterns which match no
          files (see Pathname Expansion below) to expand to a
          null string, rather than themselves.
     histchars
          The two characters which control history expansion and
          tokenization.  The first character is the _✓h_✓i_✓s_✓t_✓o_✓r_✓y
          _✓e_✓x_✓p_✓a_✓n_✓s_✓i_✓o_✓n _✓c_✓h_✓a_✓r_✓a_✓c_✓t_✓e_✓r, that is, the character which sig-
          nals the start of a history expansion, normally `!'.
          The second character is the character which signifies
          that the remainder of the line is a comment, when found
          as the first character of a word.
     nolinks
          If set, the shell does not follow symbolic links when
          executing commands 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 such as cd.
     hostname_completion_file
          Contains the name of a file in the same format as
          /_✓e_✓t_✓c/_✓h_✓o_✓s_✓t_✓s that should be read when the shell needs to
          complete a hostname.  You can change the file interac-
          tively; the next time you want to complete a hostname
          bash adds the contents of the new file to the already
          existing database.
     noclobber
          If set, bash does not overwrite an existing file with
          the >, >&, and <> redirection operators.  This variable
          may be overridden when creating output files by using
          the redirection operator >| instead of > (see also the
          -C option to the set builtin command).
     auto_resume
          This variable controls how the shell interacts with the



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          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.
     no_exit_on_failed_exec
          If this variable exists, the shell does not exit if it
          cannot execute the file specified in the exec command.
     cdable_vars
          If this is 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.
     pushd_silent
          If set, the pushd and popd builtin commands do not
          print the current directory stack after successful exe-
          cution.

EXPANSION
     Expansion is performed on the command line after it has been
     split into words.  There are seven kinds of expansion per-
     formed:  _✓b_✓r_✓a_✓c_✓e _✓e_✓x_✓p_✓a_✓n_✓s_✓i_✓o_✓n, _✓t_✓i_✓l_✓d_✓e _✓e_✓x_✓p_✓a_✓n_✓s_✓i_✓o_✓n, _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r _✓a_✓n_✓d
     _✓v_✓a_✓r_✓i_✓a_✓b_✓l_✓e _✓e_✓x_✓p_✓a_✓n_✓s_✓i_✓o_✓n, _✓c_✓o_✓m_✓m_✓a_✓n_✓d _✓s_✓u_✓b_✓s_✓t_✓i_✓t_✓u_✓t_✓i_✓o_✓n, _✓a_✓r_✓i_✓t_✓h_✓m_✓e_✓t_✓i_✓c _✓e_✓x_✓p_✓a_✓n_✓-
     _✓s_✓i_✓o_✓n, _✓w_✓o_✓r_✓d _✓s_✓p_✓l_✓i_✓t_✓t_✓i_✓n_✓g, and _✓p_✓a_✓t_✓h_✓n_✓a_✓m_✓e _✓e_✓x_✓p_✓a_✓n_✓s_✓i_✓o_✓n.

     Only brace expansion, word splitting, and pathname expansion
     can change the number of words of the expansion; other
     expansions expand a single word to a single word.  The sin-
     gle exception to this is the expansion of ``$@'' as
     explained above (see PARAMETERS).

     Brace Expansion

     _✓B_✓r_✓a_✓c_✓e _✓e_✓x_✓p_✓a_✓n_✓s_✓i_✓o_✓n is a mechanism by which arbitrary strings
     may be generated.  This mechanism is similar to _✓p_✓a_✓t_✓h_✓n_✓a_✓m_✓e
     _✓e_✓x_✓p_✓a_✓n_✓s_✓i_✓o_✓n, but the filenames generated need not exist.  Pat-
     terns to be brace expanded take the form of an optional
     _✓p_✓r_✓e_✓a_✓m_✓b_✓l_✓e, followed by a series of comma-separated strings
     between a pair of braces, followed by an optional _✓p_✓o_✓s_✓t_✓a_✓m_✓b_✓l_✓e.
     The preamble is prepended to each string contained within
     the braces, and the postamble 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'.

     Brace expansion is performed before any other expansions,
     and any characters special to other expansions are preserved
     in the result.




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     This construct is typically used as shorthand when the com-
     mon 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
     traditional versions of sh, the Bourne shell.  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 expan-
     sion.  For example, a word entered to sh as _✓f_✓i_✓l_✓e{_✓1,_✓2}
     appears identically in the output.  The same word is output
     as _✓f_✓i_✓l_✓e_✓1 _✓f_✓i_✓l_✓e_✓2 after expansion by bash.  If strict compati-
     bility with sh is desired, start bash with the -nobraceex-
     pansion flag (see OPTIONS above) or disable brace expansion
     with the +o braceexpand option to the set command (see SHELL
     BUILTIN COMMANDS below).

     Tilde Expansion

     If a word begins with a tilde character (`~'), all of the
     characters preceding the first slash (or all characters, if
     there is no slash) are treated as a possible _✓l_✓o_✓g_✓i_✓n _✓n_✓a_✓m_✓e. If
     this _✓l_✓o_✓g_✓i_✓n _✓n_✓a_✓m_✓e is the null string, the tilde is replaced
     with the value of the parameter HOME.  If HOME is unset, the
     home directory of the user executing the shell is substi-
     tuted instead.

     If a `+' follows the tilde, the value of PWD is substituted.
     If a `-' follows, the value of OLDPWD is used.

     Additionally, each word is checked for unquoted instances of
     tildes following a : or =.  In these cases, tilde substitu-
     tion is also performed.  Consequently, one may use pathnames
     with tildes in PATH, MAILPATH, and CDPATH.

     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.

     ${_✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r}
          The value of _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r is substituted.  The braces are
          required when _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r is a positional parameter with
          more than one digit, or when _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r is followed by a



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          character which is not to be interpreted as part of its
          name.

     In each of the cases below, _✓w_✓o_✓r_✓d is subject to tilde expan-
     sion, parameter expansion, command substitution, and arith-
     metic expansion.  Bash tests for a parameter that is unset
     or null; omitting the colon results in a test only for a
     parameter that is unset.

     ${_✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r:-_✓w_✓o_✓r_✓d}
          Use Default Values.  If _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r is unset or null, the
          expansion of _✓w_✓o_✓r_✓d is substituted.  Otherwise, the value
          of _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r is substituted.
     ${_✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r:=_✓w_✓o_✓r_✓d}
          Assign Default Values.  If _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r is unset or null,
          the expansion of _✓w_✓o_✓r_✓d is assigned to _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r.  The
          value of _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r is then substituted.  Positional
          parameters and special parameters may not be assigned
          to in this way.
     ${_✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r:?_✓w_✓o_✓r_✓d}
          Display Error if Null or Unset.  If _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r is null
          or unset, the expansion of _✓w_✓o_✓r_✓d (or a message to that
          effect if _✓w_✓o_✓r_✓d is not present) is written to the stan-
          dard error and the shell, if it is not interactive,
          exits.  Otherwise, the value of _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r is substi-
          tuted.
     ${_✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r:+_✓w_✓o_✓r_✓d}
          Use Alternate Value.  If _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r is null or unset,
          nothing is substituted, otherwise the expansion of _✓w_✓o_✓r_✓d
          is substituted.
     ${#_✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r}
          The length in characters of the value of _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r is
          substituted.  If _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r is * or @, the length sub-
          stituted is the length of * expanded within double
          quotes.
     ${_✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r#_✓w_✓o_✓r_✓d}
     ${_✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r##_✓w_✓o_✓r_✓d}
          The _✓w_✓o_✓r_✓d is expanded to produce a pattern just as in
          pathname expansion.  If the pattern matches the begin-
          ning of the value of _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r, then the expansion is
          the value of _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r with the shortest matching pat-
          tern deleted (the ``#'' case) or the longest matching
          pattern deleted (the ``##'' case).

     ${_✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r%_✓w_✓o_✓r_✓d}
     ${_✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r%%_✓w_✓o_✓r_✓d}
          The _✓w_✓o_✓r_✓d is expanded to produce a pattern just as in
          pathname expansion.  If the pattern matches a trailing
          portion of the value of _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r, then the expansion
          is the value of _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r with the shortest matching
          pattern deleted (the ``%'' case) or the longest match-
          ing pattern deleted (the ``%%'' case).



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     Command Substitution

     _✓C_✓o_✓m_✓m_✓a_✓n_✓d _✓s_✓u_✓b_✓s_✓t_✓i_✓t_✓u_✓t_✓i_✓o_✓n allows the output of a command to
     replace the command name.  There are two forms:

          $(_✓c_✓o_✓m_✓m_✓a_✓n_✓d)
     or
          `_✓c_✓o_✓m_✓m_✓a_✓n_✓d`

     Bash performs the expansion by executing _✓c_✓o_✓m_✓m_✓a_✓n_✓d and replac-
     ing the command substitution with the standard output of the
     command, with any trailing newlines deleted.

     When the old-style backquote form of substitution is used,
     backslash retains its literal meaning except when followed
     by $, `, or \.  When using the $(_✓c_✓o_✓m_✓m_✓a_✓n_✓d) form, all charac-
     ters between the parentheses make up the command; none are
     treated specially.

     Command substitutions may be nested.  To nest when using the
     old 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:

          $[_✓e_✓x_✓p_✓r_✓e_✓s_✓s_✓i_✓o_✓n]

     The _✓e_✓x_✓p_✓r_✓e_✓s_✓s_✓i_✓o_✓n is treated as if it were within double
     quotes, but a double quote inside the braces is not treated
     specially.  All tokens in the expression undergo parameter
     expansion, command substitution, and quote removal.  Arith-
     metic substitutions may be nested.

     The evaluation is performed according to the rules listed
     below under ARITHMETIC EVALUATION.  If _✓e_✓x_✓p_✓r_✓e_✓s_✓s_✓i_✓o_✓n is
     invalid, bash prints a message indicating failure and no
     substitution occurs.

     Word Splitting

     The shell scans the results of parameter expansion, command
     substitution, and arithmetic expansion that did not occur
     within double quotes for _✓w_✓o_✓r_✓d _✓s_✓p_✓l_✓i_✓t_✓t_✓i_✓n_✓g.





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     The shell treats each character of IFS as a delimiter, and
     splits the results of the other expansions into words on
     these characters.  If the value of IFS is exactly
     <space><tab><newline>, the default, then any sequence of IFS
     characters serves to delimit words; otherwise each
     occurrence of an IFS character is treated as a delimiter.
     If the value of IFS is null, no word splitting occurs.  IFS
     cannot be unset.

     Explicit null arguments ("" or '') are retained.  Implicit
     null arguments, resulting from the expansion of _✓p_✓a_✓r_✓a_✓m_✓e_✓t_✓e_✓r_✓s
     that have no values, are removed.

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

     Pathname Expansion

     After word splitting, bash scans each _✓w_✓o_✓r_✓d for the charac-
     ters *, ?, and [, unless the -f flag has been set.  If one
     of these characters appears, then the word is regarded as a
     _✓p_✓a_✓t_✓t_✓e_✓r_✓n, and replaced with an alphabetically sorted list of
     pathnames matching the pattern.  If no matching pathnames
     are found, and the shell variable allow_null_glob_expansion
     is unset, the word is left unchanged.  If the variable is
     set, the word is removed if no matches are found.  When a
     pattern is used for pathname generation, the character ``.''
     at the start of a name or immediately following a slash must
     be matched explicitly, unless the shell variable
     glob_dot_filenames is set.  The slash character must always
     be matched explicitly.  In other cases, the ``.'' character
     is not treated specially.

     The special pattern characters have the following meanings:

     *    Matches any string, including the null string.
     ?    Matches any single character.
     [...]
          Matches any one of the enclosed characters.  A pair of
          characters separated by a minus sign denotes a _✓r_✓a_✓n_✓g_✓e;
          any character lexically between those two characters,
          inclusive, is matched.  If the first character follow-
          ing the [ is a ! or a ^ then any character not enclosed
          is matched.  A - or ] may be matched by including it as
          the first or last character in the set.

     Quote Removal

     After the preceding expansions, all unquoted occurrences of
     the characters \, `, and " are removed.

REDIRECTION
     Before a command is executed, its input and output may be



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     _✓r_✓e_✓d_✓i_✓r_✓e_✓c_✓t_✓e_✓d using a special notation interpreted by the
     shell.  Redirection may also be used to open and close files
     for the current shell execution environment.  The following
     redirection operators may appear anywhere in a _✓s_✓i_✓m_✓p_✓l_✓e _✓c_✓o_✓m_✓-
     _✓m_✓a_✓n_✓d or may precede or follow a _✓c_✓o_✓m_✓m_✓a_✓n_✓d.  Redirections are
     processed in the order they appear, from left to right.

     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 redirec-
     tion operator is >, the redirection refers to the standard
     output (file descriptor 1).

     The word that follows the redirection operator in the fol-
     lowing descriptions is subjected to brace expansion, tilde
     expansion, parameter expansion, command substitution, arith-
     metic expansion, quote removal, and pathname expansion.  If
     it expands to more than one word, bash reports an error.

     Redirecting Input

     Redirection of input causes the file whose name results from
     the expansion of _✓w_✓o_✓r_✓d 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]<_✓w_✓o_✓r_✓d

     Redirecting Output

     Redirection of output causes the file whose name results
     from the expansion of _✓w_✓o_✓r_✓d 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]>_✓w_✓o_✓r_✓d

     If the redirection operator is >|, then the variable
     noclobber is not consulted, and the file is created regard-
     less of the value of noclobber (see Shell Variables above).

     Appending Redirected Output

     Redirection of output in this fashion causes the file whose
     name results from the expansion of _✓w_✓o_✓r_✓d to be opened for
     appending on file descriptor _✓n, or the standard output (file



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BASH(1)                   1991 July 15                    BASH(1)



     descriptor 1) if _✓n is not specified.  If the file does not
     exist it is created.

     The general format for appending output is:

          [_✓n]>>_✓w_✓o_✓r_✓d

     Redirecting Standard Output and Standard Error

     Bash 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 _✓w_✓o_✓r_✓d
     with this construct.

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

          &>_✓w_✓o_✓r_✓d
     and
          >&_✓w_✓o_✓r_✓d

     Of the two forms, the first is preferred.  This is semanti-
     cally equivalent to

          >_✓w_✓o_✓r_✓d 2>&1

     Here Documents

     This type of redirection instructs the shell to read input
     from the current source until a line containing only _✓w_✓o_✓r_✓d
     (with no trailing blanks) is seen.  All of the lines read up
     to that point are then used as the standard input for a com-
     mand.

     The format of here-documents is as follows:

          <<[-]_✓w_✓o_✓r_✓d
                  _✓h_✓e_✓r_✓e-_✓d_✓o_✓c_✓u_✓m_✓e_✓n_✓t
          _✓d_✓e_✓l_✓i_✓m_✓i_✓t_✓e_✓r

     No parameter expansion, command substitution, pathname
     expansion, or arithmetic expansion is performed on _✓w_✓o_✓r_✓d.  If
     any characters in _✓w_✓o_✓r_✓d are quoted, the _✓d_✓e_✓l_✓i_✓m_✓i_✓t_✓e_✓r is the
     result of quote removal on _✓w_✓o_✓r_✓d, and the lines in the here-
     document are not expanded.  Otherwise, all lines of the
     here-document are subjected to parameter expansion, command
     substitution, and arithmetic expansion.  In the latter case,
     the pair \<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



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     containing _✓d_✓e_✓l_✓i_✓m_✓i_✓t_✓e_✓r.  This allows here-documents within
     shell scripts to be indented in a natural fashion.

     Duplicating File Descriptors

     The redirection operator

          [_✓n]<&_✓w_✓o_✓r_✓d

     is used to duplicate input file descriptors.  If _✓w_✓o_✓r_✓d
     expands to one or more digits, the file descriptor denoted
     by _✓n is made to be a copy of that file descriptor.  If _✓w_✓o_✓r_✓d
     evaluates to -, file descriptor _✓n is closed.  If _✓n is not
     specified, the standard input (file descriptor 0) is used.

     The operator

          [_✓n]>&_✓w_✓o_✓r_✓d

     is used similarly to duplicate output file descriptors.  If
     _✓n is not specified, the standard output (file descriptor 1)
     is used.

     Opening File Descriptors for Reading and Writing

     The redirection operator

          [_✓n]<>_✓w_✓o_✓r_✓d

     causes the file whose name is the expansion of _✓w_✓o_✓r_✓d to be
     opened for both reading and writing on file descriptor _✓n, or
     as the standard input and standard output if _✓n is not speci-
     fied.

     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
     _✓d_✓i_✓r_✓l_✓i_✓s_✓t, while the command

          ls 2>&1 > dirlist

     directs only the standard output to file _✓d_✓i_✓r_✓l_✓i_✓s_✓t, because
     the standard error was duplicated as standard output before
     the standard output was redirected to _✓d_✓i_✓r_✓l_✓i_✓s_✓t.

FUNCTIONS
     A shell function, defined as described above under SHELL
     GRAMMAR, stores a series of commands for later execution.
     However, functions are executed in the context of the



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     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.  Positional
     parameter 0 is unchanged.

     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 the builtin command return is executed in a function, the
     function completes and execution resumes with the next com-
     mand after the function call.  When a function completes,
     the values of the positional parameters and the special
     parameter # are restored to the values they had prior to
     function execution.

     Function names may be listed with the -f option to the
     declare or typeset builtin commands.  Functions may be
     exported so that subshells automatically have them defined
     with the -f option to the export builtin.

     Functions may be recursive.  No limit is imposed on the
     number of recursive calls.

ALIASES
     The shell maintains a list of _✓a_✓l_✓i_✓a_✓s_✓e_✓s that may be set and
     unset with the alias and unalias builtin commands.  The
     first word of each command is checked to see if it has an
     alias.  If so, that word is replaced by the text of the
     alias.  The alias name and the replacement text may contain
     any valid shell input, including the _✓m_✓e_✓t_✓a_✓c_✓h_✓a_✓r_✓a_✓c_✓t_✓e_✓r_✓s listed
     above.  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 _✓b_✓l_✓a_✓n_✓k, then the next com-
     mand 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, a la csh.  If arguments are needed, a shell function
     should be used.

     The rules concerning the definition and use of aliases are
     somewhat confusing.  Bash always reads at least one complete
     line of input before executing any of the commands on that



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     line.  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.  This means that the com-
     mands 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 the
     function definition is read, not when the function is exe-
     cuted, because a function definition is itself a compound
     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.

     Aliases are not expanded when the shell is not interactive.

     Note that for almost every purpose, aliases are superseded
     by shell functions.

JOB CONTROL
     _✓J_✓o_✓b _✓c_✓o_✓n_✓t_✓r_✓o_✓l refers to the ability to selectively stop
     (_✓s_✓u_✓s_✓p_✓e_✓n_✓d) the execution of processes and continue (_✓r_✓e_✓s_✓u_✓m_✓e)
     their execution at a later point.  A user typically employs
     this facility via an interactive interface supplied jointly
     by the system's terminal driver and bash.

     The shell associates a _✓j_✓o_✓b 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 _✓b_✓a_✓c_✓k_✓g_✓r_✓o_✓u_✓n_✓d), it prints a line that looks like:

          [1] 25647

     indicating that this job is job number 1 and that the pro-
     cess ID of the single process in the job is 25647.  Bash
     uses the _✓j_✓o_✓b abstraction as the basis for job control.

     To facilitate the implementation of the user interface to
     job control, the system maintains the notion of a _✓c_✓u_✓r_✓r_✓e_✓n_✓t
     _✓t_✓e_✓r_✓m_✓i_✓n_✓a_✓l _✓p_✓r_✓o_✓c_✓e_✓s_✓s _✓g_✓r_✓o_✓u_✓p _✓I_✓D.  Members of this process group
     (processes whose process group ID is equal to the current
     terminal process group ID) receive keyboard-generated sig-
     nals such as SIGINT.  These processes are said to be in the
     _✓f_✓o_✓r_✓e_✓g_✓r_✓o_✓u_✓n_✓d.  _✓B_✓a_✓c_✓k_✓g_✓r_✓o_✓u_✓n_✓d 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 write to the terminal.
     Background processes which attempt to read from (write to)
     the terminal are sent a SIGTTIN (SIGTTOU) signal by the ter-
     minal driver, which, unless caught, causes the process to
     stop.




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     If the operating system on which bash is running supports
     job control, bash allows you to use it.  Typing the _✓s_✓u_✓s_✓p_✓e_✓n_✓d
     character (typically ^Z, Control-Z) while a process is run-
     ning causes that process to be stopped and returns you to
     bash.  Typing the _✓d_✓e_✓l_✓a_✓y_✓e_✓d _✓s_✓u_✓s_✓p_✓e_✓n_✓d 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.  You 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 name.  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, would
     refer 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 _✓c_✓u_✓r_✓r_✓e_✓n_✓t _✓j_✓o_✓b, which is the last job
     stopped while it was in the foreground.  The _✓p_✓r_✓e_✓v_✓i_✓o_✓u_✓s _✓j_✓o_✓b
     may be referenced using %-.  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 -.

     Simply naming a job can be used to bring it into the fore-
     ground:  %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 variable notify is set,
     bash reports such changes immediately.  (See also the -o
     notify option to the set builtin command.)

     If you attempt to exit bash while jobs are stopped, the
     shell prints a message warning you.  You may then use the
     jobs command to inspect their status.  If you do this, or
     try to exit again immediately, you are not warned again, and
     the stopped jobs are terminated.

SIGNALS
     When bash is interactive, it ignores SIGTERM (so that kill 0
     does not kill an interactive shell), and SIGINT is caught
     and handled (so that wait is interruptible).  In all cases,



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     bash ignores SIGQUIT.  If job control is in effect, bash
     ignores SIGTTIN, SIGTTOU, and SIGTSTP.

     Synchronous jobs started by bash have signals set to the
     values inherited by the shell from its parent.  Background
     jobs (jobs started with &) ignore SIGINT and SIGQUIT.  Com-
     mands run as a result of command substitution ignore the
     keyboard-generated job control signals SIGTTIN, SIGTTOU, and
     SIGTSTP.

COMMAND EXECUTION
     After a command has been split into words, if it results in
     a simple command and an optional list of arguments, the fol-
     lowing 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 FUNC-
     TIONS.  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.
     If the search is unsuccessful, the shell prints an error
     message and returns a nonzero exit status.

     If the search is successful, or if the command name contains
     one or more slashes, the shell executes the named program.
     Argument 0 is set to the name given, and the remaining argu-
     ments to the command are set to the arguments given, if any.

     If this execution fails because the file is not in execut-
     able format, and the file is not a directory, it is assumed
     to be a _✓s_✓h_✓e_✓l_✓l _✓s_✓c_✓r_✓i_✓p_✓t, a file containing shell commands.  A
     subshell is spawned to execute it.  This subshell reinitial-
     izes 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 them-
     selves.  The arguments to the interpreter consist of a sin-
     gle optional argument following the interpreter name on the
     first line of the program, followed by the name of the pro-
     gram, followed by the command arguments, if any.




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ENVIRONMENT
     When a program is invoked it is given an array of strings
     called the _✓e_✓n_✓v_✓i_✓r_✓o_✓n_✓m_✓e_✓n_✓t.  This is a list of _✓n_✓a_✓m_✓e-_✓v_✓a_✓l_✓u_✓e pairs,
     of the form _✓n_✓a_✓m_✓e=_✓v_✓a_✓l_✓u_✓e.

     The shell allows you to manipulate the environment in
     several ways.  On invocation, the shell scans its own
     environment and creates a parameter for each name found,
     automatically marking it for _✓e_✓x_✓p_✓o_✓r_✓t 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 modi-
     fied in the shell, less any pairs removed by the unset com-
     mand, plus any additions via the export and declare -x com-
     mands.

     The environment for any _✓s_✓i_✓m_✓p_✓l_✓e _✓c_✓o_✓m_✓m_✓a_✓n_✓d or function may be
     augmented temporarily by prefixing it with parameter assign-
     ments, as described above in PARAMETERS.  These assignment
     statements affect only the environment seen by that command.

     If the -k flag is set (see the set builtin command below),
     then _✓a_✓l_✓l parameter assignments are placed in the environment
     for a command, not just those that precede the command name.

EXIT STATUS
     For the purposes of the shell, 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, bash
     uses the value of 128+signal as the exit status.

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

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 allows the prompt to be customized by insert-
     ing a number of backslash-escaped special characters that
     are decoded as follows:
          \t   the time
          \d   the date
          \n   CRLF
          \s   the name of the shell, the basename of $0 (the



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               portion following the final slash)
          \w   the current working directory
          \W   the basename of the current working directory
          \u   the username of the current user
          \h   the hostname
          \#   the command number of this command
          \!   the history number of this command
          \$   if the effective UID is 0, a #, otherwise a $
          \nnn character code in octal
          \\   a backslash

     After the string is decoded, if the variable NO_PROMPT_VARS
     is not set, it is expanded via parameter expansion, command
     substitution, arithmetic expansion, and word splitting.

READLINE
     This is the library that handles reading input when using an
     interactive shell, unless the -nolineediting option is
     given.  By default, the line editing commands are similar to
     those of emacs.  A vi-style line editing interface is also
     available.

     In this section, the emacs-style notation is used to denote
     keystrokes.  Control keys are denoted by C-_✓k_✓e_✓y, e.g. C-n
     means Control-N.  Similarly, _✓m_✓e_✓t_✓a keys are denoted by M-_✓k_✓e_✓y,
     so M-x means Meta-X.  (On keyboards without a _✓m_✓e_✓t_✓a key, M-_✓x
     means ESC _✓x, i.e. press the Escape key then the _✓x key.  The
     combination M-C-_✓x means ESC-Control-_✓x, or press the Escape
     key then hold the Control key while pressing the _✓x key.)

     The default key-bindings may be changed with an ~/._✓i_✓n_✓p_✓u_✓t_✓r_✓c
     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 ~/._✓i_✓n_✓p_✓u_✓t_✓r_✓c would make M-C-u execute the command
     _✓u_✓n_✓i_✓v_✓e_✓r_✓s_✓a_✓l-_✓a_✓r_✓g_✓u_✓m_✓e_✓n_✓t.

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

     Placing

          set editing-mode vi

     into a ~/._✓i_✓n_✓p_✓u_✓t_✓r_✓c file causes bash to start with a _✓v_✓i-like
     editing mode.  The editing mode may be switched during
     interactive use by using the -o option to the set builtin



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     command (see SHELL BUILTIN COMMANDS below).

     You can have readline use a single line for display, scrol-
     ling the input between the two borders by placing

          set horizontal-scroll-mode On

     into a ~/._✓i_✓n_✓p_✓u_✓t_✓r_✓c file.

     The following is a list of the names of the commands and the
     default key-strokes to get them.

     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.
     backward-word (M-b)
          Move back to the start of this, or the previous, word.
     clear-screen (C-l)
          Clear the screen leaving the current line at the top of
          the screen.

     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 history_control variable.
          If this line was a history line, then restore the his-
          tory line to its original state.
     previous-history (C-p)
          Fetch the previous command from the history list, mov-
          ing 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, the first line
          entered.
     end-of-history (M->)
          Move to the end of the input history, i.e., the line
          you are entering.
     reverse-search-history (C-r)
          Search backward starting at the current line and moving



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          `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.
     shell-expand-line (M-C-e)
          Expand the line the way the shell does when it reads
          it.  This performs alias and history expansion.  See
          HISTORY below.
     insert-last-argument (M-., M-_)
          Insert the last argument to the previous command (the
          last word on the previous line).
     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
          file for editing.

     Commands for Changing Text

     delete-char (C-d)
          Delete the character under the cursor.  If the cursor
          is at the beginning of the line, and there are no char-
          acters in the line, and the last character typed was
          not C-d, then return EOF.
     backward-delete-char (Rubout)
          Delete the character behind the cursor.  A numeric arg
          says to kill the characters instead of deleting them.
     quoted-insert (C-q, C-v)
          Add the next character that you type to the line verba-
          tim.  This is how to insert characters like C-q, for
          example.
     tab-insert (M-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 char-
          acter at point.  Point moves forward as well.  If point
          is at the end of the line, then transpose the two char-
          acters before point.  Negative arguments don't work.
     transpose-words (M-t)
          Drag the word behind the cursor past the word in front
          of the cursor moving the cursor over that word as well.
     upcase-word (M-u)
          Uppercase the current (or following) word.  With a
          negative argument, do the previous word, but do not
          move point.
     downcase-word (M-l)
          Lowercase the current (or following) word.  With a
          negative argument, do the previous word, but do not
          move point.
     capitalize-word (M-c)



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          Capitalize the current (or following) word.  With a
          negative argument, do the previous word, but do not
          move point.

     Killing and Yanking

     kill-line (C-k)
          Kill the text from the current cursor position to the
          end of the line.  This saves the killed text on the
          kill-ring.  (see below)
     backward-kill-line
          Kill backward to the beginning of the line.  This is
          normally unbound, in favor of unix-line-discard, which
          emulates the behavior of the standard Unix terminal
          driver.
     kill-word (M-d)
          Kill from the cursor to the end of the current word, or
          if between words, to the end of the next word.
     backward-kill-word (M-Rubout)
          Kill the word behind the cursor.
     unix-line-discard (C-u)
          Do what C-u used to do in Unix line input.  We save the
          killed text on the kill-ring, though.
     unix-word-rubout (C-w)
          Do what C-w used to do in Unix line input.  The killed
          text is saved on the kill-ring.  This is different than
          backward-kill-word because the word boundaries differ.
     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'.

     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
          Do what C-u does in _✓e_✓m_✓a_✓c_✓s. By default, this is not
          bound to a key.

     Completing

     complete (TAB)
          Attempt to perform completion on the text before point.
          Bash attempts completion treating the text as a vari-
          able (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.



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     possible-completions (M-?)
          List the possible completions of the text before point.
     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.

     Miscellaneous

     abort (C-g)
          Abort the current editing command and ring the
          terminal's bell.
     do-uppercase-version (M-a, M-b, ...)
          Run the command that is bound to the uppercased key.
     prefix-meta (ESC)
          Metafy the next character typed.  This is for people
          without a meta key.  ESC f is equivalent to Meta-f.
     undo (C-_)
          Incremental undo, separately remembered for each line.
     revert-line (M-r)
          Undo all changes made to this line.  This is like typ-
          ing the `undo' command enough times to get back to the
          beginning.
     display-shell-version (C-x C-v)
          Display version information about the current instance
          of bash.
     emacs-editing-mode (C-e)
          When in vi editing mode, this causes a switch to emacs
          editing mode.
     vi-editing-mode (M-C-j or M-C-m)
          When in emacs editing mode, this causes a switch to vi
          editing mode.




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HISTORY
     The shell supports a history expansion feature that is simi-
     lar to the history expansion in csh.  This section describes
     what syntax features are available.

     History expansion is performed immediately after a complete
     line is read, before the shell breaks it into words.  It
     takes place in two parts.  The first is determining which
     line from the previous history to use during substitution.
     The second is to select portions of that line for inclusion
     into the current one.  The line selected from the previous
     history is the _✓e_✓v_✓e_✓n_✓t, and the portions of that line that are
     acted upon are _✓w_✓o_✓r_✓d_✓s.  The line is broken into words in the
     same fashion as when reading input, so that several English,
     or Unix, words surrounded by quotes are considered as one
     word.  Only backslash (\) can quote the history escape char-
     acter, which is ! by default.

     Event Designators

     An event designator is a reference to a command line entry
     in the history list.

     !    Start a history substitution, except when followed by a
          <space>, <tab>, <newline>, = or (.
     !!   Refer to the previous command.  This is a synonym for
          `!-1'.
     !_✓n   Refer to command line _✓n.
     !-_✓n  Refer to the current command line minus _✓n.
     !_✓s_✓t_✓r_✓i_✓n_✓g
          Refer to the most recent command starting with _✓s_✓t_✓r_✓i_✓n_✓g.
     !?_✓s_✓t_✓r_✓i_✓n_✓g[?]
          Refer to the most recent command containing _✓s_✓t_✓r_✓i_✓n_✓g.

     Word Designators

     A : separates the event specification from the word designa-
     tor.  It can 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 a 0 (zero).

     #    The entire command line typed so far.  This means the
          current command, not the previous command, so it really
          isn't a word designator, and doesn't belong in this
          section.
     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 argument.
     %    The word matched by the most recent `?_✓s_✓t_✓r_✓i_✓n_✓g?' search.



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     _✓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.

     Modifiers

     After the optional word designator, you can add a sequence
     of one or more of the following modifiers, each preceded by
     a `:'.

     h    Remove a trailing pathname component, leaving only the
          head.
     r    Remove a trailing suffix of the form ".xxx", leaving
          the basename.
     e    Remove all but the suffix.
     t    Remove all leading pathname components, leaving the
          tail.
     p    Print the new command but do not execute it.  This
          takes effect immediately, so it should be the last
          specifier on the line.

ARITHMETIC EVALUATION
     The shell allows arithmetic expressions to be evaluated,
     under certain circumstances (see the let builtin command and
     Arithmetic Expansion).  Evaluation is done in long integers
     with no check for overflow, though division by 0 is trapped
     and flagged as an error.  The following list of operators is
     grouped into levels of equal-precedence operators.  The lev-
     els are listed in order of decreasing precedence.

     -    unary minus
     !    logical NOT
     * / %
          multiplication, division, remainder
     + -  addition, subtraction
     <= >= < >
          comparison
     == !=
          equality and inequality
     =    assignment

     Shell variables are allowed as operands; parameter expansion
     is performed before the expression is evaluated. The value
     of a parameter is coerced to a long integer within an
     expression.  A shell variable need not have its integer
     attribute turned on to be used in an expression.

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



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SHELL BUILTIN COMMANDS
     : [_✓a_✓r_✓g_✓u_✓m_✓e_✓n_✓t_✓s]
          No effect; the command does nothing beyond expanding
          _✓a_✓r_✓g_✓u_✓m_✓e_✓n_✓t_✓s and performing any specified redirections.  A
          zero exit code is returned.
          Read and execute commands from _✓f_✓i_✓l_✓e_✓n_✓a_✓m_✓e in the current
          shell environment and return the exit status of the
          last command executed from _✓f_✓i_✓l_✓e_✓n_✓a_✓m_✓e.  Pathnames in PATH
          are used to find the directory containing _✓f_✓i_✓l_✓e_✓n_✓a_✓m_✓e, if
          _✓f_✓i_✓l_✓e_✓n_✓a_✓m_✓e does not contain a slash.  The file searched
          for in PATH need not be executable.  The current direc-
          tory is searched if no file is found in PATH.  The
          return status is the status of the last command exited
          within the script (true if no commands are executed),
          and false if _✓f_✓i_✓l_✓e_✓n_✓a_✓m_✓e is not found.

     alias [_✓n_✓a_✓m_✓e[=_✓v_✓a_✓l_✓u_✓e] ...]
          Alias with no arguments prints the list of aliases in
          the form _✓n_✓a_✓m_✓e=_✓v_✓a_✓l_✓u_✓e on standard output.  When arguments
          are supplied, an alias is defined for each _✓n_✓a_✓m_✓e whose
          _✓v_✓a_✓l_✓u_✓e is given.  A trailing space in _✓v_✓a_✓l_✓u_✓e causes the
          next word to be checked for alias substitution when the
          alias is expanded.  Alias returns true unless a _✓n_✓a_✓m_✓e is
          given for which no alias has been defined.

     bg [_✓j_✓o_✓b_✓s_✓p_✓e_✓c]
          Place _✓j_✓o_✓b_✓s_✓p_✓e_✓c in the background, as if it had been
          started with &.  If _✓j_✓o_✓b_✓s_✓p_✓e_✓c is not present, the shell's
          notion of the _✓c_✓u_✓r_✓r_✓e_✓n_✓t _✓j_✓o_✓b is used.

     bind [-lvd] [-q _✓n_✓a_✓m_✓e]
     bind -f _✓f_✓i_✓l_✓e_✓n_✓a_✓m_✓e
     bind _✓k_✓e_✓y_✓s_✓e_✓q:_✓f_✓u_✓n_✓c_✓t_✓i_✓o_✓n-_✓n_✓a_✓m_✓e
          Display current readline key and function bindings, or
          bind a key sequence to a readline function or macro.
          The binding syntax accepted is identical to that of
          ._✓i_✓n_✓p_✓u_✓t_✓r_✓c, but each binding must be passed as a separate
          argument; e.g. '"\C-x\C-r": re-read-init-file'.
          Options, if supplied, have the following meanings:
          -l   List the names of all readline functions
          -v   List current function names and bindings
          -d   Dump function names and bindings in such a way
               that they can be re-read
          -f _✓f_✓i_✓l_✓e_✓n_✓a_✓m_✓e
               Read key bindings from _✓f_✓i_✓l_✓e_✓n_✓a_✓m_✓e
          -q _✓f_✓u_✓n_✓c_✓t_✓i_✓o_✓n
               Query about which keys invoke the named _✓f_✓u_✓n_✓c_✓t_✓i_✓o_✓n

     break [_✓n]
          Exit from within a for, while, or until loop.  If _✓n is
          specified, break _✓n levels.  _✓n must be _✓> 1.  If _✓n is
          greater than the number of enclosing loops, all



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          enclosing loops are exited.  The return value is 0
          unless the shell is not executing a loop when break is
          executed.

     builtin [_✓s_✓h_✓e_✓l_✓l-_✓b_✓u_✓i_✓l_✓t_✓i_✓n [_✓a_✓r_✓g_✓u_✓m_✓e_✓n_✓t_✓s]]
          Execute the specified shell builtin, passing it _✓a_✓r_✓g_✓u_✓-
          _✓m_✓e_✓n_✓t_✓s, and return its exit status.  This is useful when
          you wish to define a function whose name is the same as
          a shell builtin, but need the functionality of the
          builtin within the function itself.  The cd builtin is
          commonly redefined this way.

     cd [_✓d_✓i_✓r]
          Change the current directory to _✓d_✓i_✓r.  The variable HOME
          is the default _✓d_✓i_✓r.  The variable CDPATH defines the
          search path for the directory containing _✓d_✓i_✓r.  Alterna-
          tive directory names are separated by a colon (:).  A
          null directory name in CDPATH is the same as the
          current directory, i.e. ``.''.  If _✓d_✓i_✓r begins with a
          slash (/), then CDPATH is not used.  An argument of -
          is equivalent to $OLDPWD.  The return value is true if
          the directory was successfully changed; false other-
          wise.

     command [-p] [_✓c_✓o_✓m_✓m_✓a_✓n_✓d [_✓a_✓r_✓g ...]]
          Run _✓c_✓o_✓m_✓m_✓a_✓n_✓d with _✓a_✓r_✓g_✓s 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 _✓c_✓o_✓m_✓m_✓a_✓n_✓d is performed using a
          default value for PATH that is guaranteed to find all
          of the standard utilities.  An argument of -- disables
          option checking for the rest of the arguments.  If an
          error occurred or _✓c_✓o_✓m_✓m_✓a_✓n_✓d cannot be found, the exit
          status is 127.  Otherwise, the exit status of the com-
          mand builtin is the exit status of _✓c_✓o_✓m_✓m_✓a_✓n_✓d.

     continue [_✓n]
          Resume the next iteration of the enclosing for, while,
          or until 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 the shell is not executing a loop when con-
          tinue is executed.

     declare [-frxi] [_✓n_✓a_✓m_✓e[=_✓v_✓a_✓l_✓u_✓e]]
     typeset [-frxi] [_✓n_✓a_✓m_✓e[=_✓v_✓a_✓l_✓u_✓e]]
          Declare variables and/or give them attributes.  If no
          _✓n_✓a_✓m_✓es are given, then display the values of variables
          instead.
          -f   Use function names only
          -r   Make _✓n_✓a_✓m_✓es readonly.  These names cannot then be



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               assigned values by subsequent assignment state-
               ments.
          -x   Mark _✓n_✓a_✓m_✓es for export to subsequent commands via
               the environment.
          -i   The variable is treated as an integer; arithmetic
               evaluation (see ARITHMETIC EVALUATION ) is per-
               formed when the variable is assigned a value.

          Using `+' instead of `-' turns off the attribute
          instead.  When used in a function, makes _✓n_✓a_✓m_✓es local,
          as with the local command.

     dirs Display the list of currently remembered directories.
          Directories are added to the list with the pushd com-
          mand; the popd command moves back up through the list.

     echo [-ne] [_✓a_✓r_✓g ...]
          Output the _✓a_✓r_✓gs, separated by spaces.  If -n is speci-
          fied, the trailing newline is suppressed.  If the -e
          option is given, interpretation of the following
          backslash-escaped characters is enabled:
          \a   alert (bell)
          \b   backspace
          \c   suppress trailing newline
          \f   form feed
          \n   new line
          \r   carriage return
          \t   horizontal tab
          \v   vertical tab
          \\   backslash
          \nnn the character whose ASCII code is _✓n_✓n_✓n (octal)

     enable [-n] [_✓n_✓a_✓m_✓e ...]
          Enable and disable builtin shell commands.  This allows
          the execution of a disk command which has the same name
          as a shell builtin without specifying a full pathname.
          If -n is used, each _✓n_✓a_✓m_✓e is disabled; otherwise, _✓n_✓a_✓m_✓e_✓s
          are enabled.  For example, to use the test found in
          PATH instead of the shell builtin version, type
          ``enable -n test''.

     eval [_✓a_✓r_✓g ...]
          The _✓a_✓r_✓gs are read and concatenated together into a sin-
          gle command.  This command is then read and executed by
          the shell, and its exit status is returned as the value
          of the eval command.  If there are no _✓a_✓r_✓g_✓s, or only
          null arguments, eval returns true.

     exec [[-] _✓c_✓o_✓m_✓m_✓a_✓n_✓d [_✓a_✓r_✓g_✓u_✓m_✓e_✓n_✓t_✓s]]
          If _✓c_✓o_✓m_✓m_✓a_✓n_✓d is specified, it replaces the shell.  No new
          process is created.  The _✓a_✓r_✓g_✓u_✓m_✓e_✓n_✓t_✓s become the arguments
          to _✓c_✓o_✓m_✓m_✓a_✓n_✓d.  If the first argument is -, the shell



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          places a dash in the zeroth arg passed to _✓c_✓o_✓m_✓m_✓a_✓n_✓d.
          This is what login does.  If the file cannot be exe-
          cuted for some reason, the shell exits, unless the
          shell variable no_exit_on_failed_exec exists.  If _✓c_✓o_✓m_✓-
          _✓m_✓a_✓n_✓d is not specified, any redirections take effect in
          the current shell.

     exit [_✓n]
     bye [_✓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 [-npf] [_✓n_✓a_✓m_✓e[=_✓w_✓o_✓r_✓d]] ...
          The supplied _✓n_✓a_✓m_✓e_✓s are marked for automatic export to
          the environment of subsequently executed commands.  If
          the -f option is given, the _✓n_✓a_✓m_✓e_✓s refer to functions.
          If no _✓n_✓a_✓m_✓e_✓s are given, or if the -p option is supplied,
          a list of all names that are exported in this shell is
          printed.  The -n option causes the export property to
          be removed from the named variables.  An argument of --
          disables option checking for the rest of the arguments.
          export returns an exit status of true unless an illegal
          option is encountered.

     fc [-e _✓e_✓n_✓a_✓m_✓e] [-nlr] [_✓f_✓i_✓r_✓s_✓t] [_✓l_✓a_✓s_✓t]
     fc -s [_✓p_✓a_✓t=_✓r_✓e_✓p] [_✓c_✓m_✓d]
          Fix Command.  In the first form, a range of commands
          from _✓f_✓i_✓r_✓s_✓t to _✓l_✓a_✓s_✓t is selected from the history list.
          _✓F_✓i_✓r_✓s_✓t and _✓l_✓a_✓s_✓t 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 nega-
          tive number is used as an offset from the current com-
          mand number).  If _✓l_✓a_✓s_✓t is not specified it is set to
          the current command for listing (so that fc -l -10
          prints the last 10 commands) and to _✓f_✓i_✓r_✓s_✓t otherwise.
          If _✓f_✓i_✓r_✓s_✓t is not specified it is set to the previous
          command for editing and -16 for listing.

          The -n flag suppresses the command numbers when list-
          ing.  The -r flag reverses the order of the commands.
          If the -l flag is given, the commands are listed on
          standard output.  Otherwise, the editor given by _✓e_✓n_✓a_✓m_✓e
          is invoked on a file containing those commands.  If
          _✓e_✓n_✓a_✓m_✓e 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, _✓v_✓i is used.  When editing is
          complete, the edited commands are echoed and executed.

          In the second form, the command is re-executed after
          the substitution _✓o_✓l_✓d=_✓n_✓e_✓w is performed.  A useful alias



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          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.

     fg [_✓j_✓o_✓b_✓s_✓p_✓e_✓c]
          Place _✓j_✓o_✓b_✓s_✓p_✓e_✓c in the foreground, and make it the
          current job.  If _✓j_✓o_✓b_✓s_✓p_✓e_✓c is not present, the shell's
          notion of the _✓c_✓u_✓r_✓r_✓e_✓n_✓t _✓j_✓o_✓b is used.

     getopts _✓o_✓p_✓t_✓s_✓t_✓r_✓i_✓n_✓g _✓n_✓a_✓m_✓e [_✓a_✓r_✓g_✓s]
          getopts is used by shell procedures to parse positional
          parameters.  _✓o_✓p_✓t_✓s_✓t_✓r_✓i_✓n_✓g contains the option letters to
          be recognized; if a letter is followed by a colon, the
          option is expected to have an argument, which should be
          separated from it by white space.  Each time it is
          invoked, getopts places the next option in the shell
          variable _✓n_✓a_✓m_✓e, initializing _✓n_✓a_✓m_✓e 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 argu-
          ment into the variable OPTARG.

          getopts can report errors in two ways.  If the first
          character of _✓o_✓p_✓t_✓s_✓t_✓r_✓i_✓n_✓g is a colon, _✓s_✓i_✓l_✓e_✓n_✓t error report-
          ing is used.  In normal operation diagnostic messages
          are printed when illegal options or missing option
          arguments are encountered.  If the variable OPTERR is
          set to 0, no error message will be displayed, even if
          the first character of _✓o_✓p_✓t_✓s_✓t_✓r_✓i_✓n_✓g is not a colon.

          If an illegal option is seen, getopts places ? into
          _✓n_✓a_✓m_✓e and, if not silent, prints an error message and
          unsets OPTARG.  If getopts is silent, the option char-
          acter found is placed in OPTARG and no diagnostic mes-
          sage is printed.

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

          getopts normally parses the positional parameters, but
          if more arguments are given in _✓a_✓r_✓g_✓s, getopts parses
          those instead.  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 [-r] [_✓n_✓a_✓m_✓e]
          For each _✓n_✓a_✓m_✓e, the full pathname of the command is



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          determined and remembered.  The -r option causes the
          shell to forget all remembered locations.  If no argu-
          ments are given, information about remembered commands
          is printed.  An argument of -- disables option checking
          for the rest of the arguments.  The return status is
          true unless a _✓n_✓a_✓m_✓e is not found or an illegal option is
          supplied.

     help [_✓p_✓a_✓t_✓t_✓e_✓r_✓n]
          Display helpful information about builtin commands.  If
          _✓p_✓a_✓t_✓t_✓e_✓r_✓n is specified, help gives detailed help on all
          commands matching _✓p_✓a_✓t_✓t_✓e_✓r_✓n; otherwise a list of the
          builtins is printed.

     history [_✓n]
     history -rwan [_✓f_✓i_✓l_✓e_✓n_✓a_✓m_✓e]
          With no options, display the command history list with
          line numbers.  Lines listed with with a * have been
          modified.  An argument of _✓n lists only the last _✓n
          lines.  If a non-option argument is supplied, it is
          used as the name of the history file; if not, the value
          of HISTFILE (default ~/._✓b_✓a_✓s_✓h__✓h_✓i_✓s_✓t_✓o_✓r_✓y) is used.
          Options, if supplied, have the following meanings:
          -a   Append the ``new'' history lines (history lines
               entered since the beginning of the current bash
               session) 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 use them
               as the current history
          -w   write the current history to the history file,
               overwriting the history file's contents.

     jobs [-lnp] [ _✓j_✓o_✓b_✓s_✓p_✓e_✓c ... ]
          Lists the active jobs.  The -l option lists process IDs
          in addition to the normal information; the -p option
          lists only the process ID of the job's process group
          leader.  The -n option displays only jobs that have
          changed status since last notfied.  If _✓j_✓o_✓b_✓s_✓p_✓e_✓c is
          given, output is restricted to information about that
          job.

     kill [-s sigspec | -sigspec] [_✓p_✓i_✓d | _✓j_✓o_✓b_✓s_✓p_✓e_✓c] ...
     kill -l [_✓s_✓i_✓g_✓n_✓u_✓m]
          Send the signal named by _✓s_✓i_✓g_✓s_✓p_✓e_✓c to the processes named
          by _✓p_✓i_✓d or _✓j_✓o_✓b_✓s_✓p_✓e_✓c.  _✓s_✓i_✓g_✓s_✓p_✓e_✓c is either a signal name
          such as SIGKILL or a signal number.  If _✓s_✓i_✓g_✓s_✓p_✓e_✓c is a
          signal name, the name is case insensitive and may be
          given with or without the SIG prefix.  If _✓s_✓i_✓g_✓s_✓p_✓e_✓c is
          not present, then SIGTERM is assumed.  An argument of



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          -l lists the signal names.  If any arguments are sup-
          plied when -l is given, the names of the specified sig-
          nals are listed.  An argument of -- disables option
          checking for the rest of the arguments.  kill returns
          true if at least one signal was successfully sent, or
          false if an error occurs.

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

     local [_✓n_✓a_✓m_✓e[=_✓v_✓a_✓l_✓u_✓e]]
          Create a local variable named _✓n_✓a_✓m_✓e, and assign it
          _✓v_✓a_✓l_✓u_✓e.  When local is used within a function, it causes
          the variable _✓n_✓a_✓m_✓e to have a visible scope restricted to
          that function and its children.  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.

     logout
          Exit a login shell.

     popd [+/-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.
          +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 variable pushd_silent is unset and the popd com-
          mand is successful, a dirs is performed as well.

     pushd _✓d_✓i_✓r
     pushd +/-n
          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,
          exchanges the top two directories.
          +n   Rotates the stack so that the _✓nth directory
               (counting from the left of the list shown by dirs)
               is at the top.
          -n   Rotates the stack so that the _✓nth directory
               (counting from the right) is at the top.
          dir  adds _✓d_✓i_✓r to the directory stack at the top, making



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               it the new current working directory.

          If the variable pushd_silent is not set and the pushd
          command is successful, a dirs is performed as well.

     pwd  Print the absolute pathname of the current working
          directory.  The path printed contains no symbolic links
          (but see the description of nolinks under Shell Vari-
          ables above).

     read [-r] [_✓n_✓a_✓m_✓e ...]
          One line is read from the standard input, and the first
          word is assigned to the first _✓n_✓a_✓m_✓e, the second word to
          the second _✓n_✓a_✓m_✓e, and so on, with leftover words
          assigned to the last _✓n_✓a_✓m_✓e.  Only the characters in IFS
          are recognized as word delimiters.  The return code is
          zero, unless end-of-file is encountered.  If the -r
          option is given, a backslash-newline pair is not
          ignored, and the backslash is considered to be part of
          the line.

     readonly [-pf] [_✓n_✓a_✓m_✓e ...]
          The given _✓n_✓a_✓m_✓e_✓s are marked readonly and the values of
          these _✓n_✓a_✓m_✓e_✓s may not be changed by subsequent assign-
          ment.  If the -f option is supplied, the functions
          corresponding to the _✓n_✓a_✓m_✓e_✓s are so marked.  If no argu-
          ments are given, or if the -p option is supplied, a
          list of all readonly names is printed.  An argument of
          -- disables option checking for the rest of the argu-
          ments.

     return [_✓n]
          Causes a function to exit with the return value speci-
          fied by _✓n.  If _✓n is omitted, the return status is that
          of the last command executed in the function body.  If
          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.

     set [-aefhknotuvxldCH] [_✓a_✓r_✓g ...]
          -a      Automatically mark variables which are modified
                  or created for export to the environment of
                  subsequent commands.
          -e      Exit immediately if a _✓s_✓i_✓m_✓p_✓l_✓e-_✓c_✓o_✓m_✓m_✓a_✓n_✓d (see SHELL
                  GRAMMAR above) exits with a non-zero status.
                  The shell does not exit if the command that
                  fails is part of an _✓u_✓n_✓t_✓i_✓l or _✓w_✓h_✓i_✓l_✓e loop, part
                  of an _✓i_✓f statement, part of a && or || list, or
                  if the command's return value is being inverted
                  via !.



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          -f      Disable pathname expansion.
          -h      Locate and remember function commands as func-
                  tions are defined.  Function commands are nor-
                  mally looked up when the function is executed.
          -k      All keyword arguments are placed in the
                  environment for a command, not just those that
                  precede the command name.
          -m      Monitor mode.  Job control is enabled.  This
                  flag is on by default for interactive shells on
                  systems that support it (see JOB CONTROL
                  above).  Background processes run in a separate
                  process group and a line containing their exit
                  status is printed upon their completion.
          -n      Read commands but do not execute them.  This
                  may be used to check a shell script for syntax
                  errors.  This is ignored for interactive
                  shells.
          -o _✓o_✓p_✓t_✓i_✓o_✓n-_✓n_✓a_✓m_✓e
                  The _✓o_✓p_✓t_✓i_✓o_✓n-_✓n_✓a_✓m_✓e can be one of the following:
                  allexport
                          Same as -a.
                  braceexpand
                          The shell performs curly brace expan-
                          sion (see Brace Expansion above).  This
                          is on by default.
                  emacs   Use an emacs-style command line editing
                          interface.
                  errexit Same as -e.
                  histexpand
                          Same as -H.
                  ignoreeof
                          The effect is as if the shell command
                          `IGNOREEOF=10' had been executed (see
                          Shell Variables above).
                  monitor Same as -m.
                  noclobber
                          Same as -C.
                  noexec  Same as -n.
                  noglob  Same as -f.
                  nohash  Same as -d.
                  notify  The effect is as if the shell command
                          `notify=' had been executed (see Shell
                          Variables above).
                  nounset Same as -u.
                  verbose Same as -v.
                  vi      Use a vi-style command line editing
                          interface.
                  xtrace  Same as -x.
                  If no _✓o_✓p_✓t_✓i_✓o_✓n-_✓n_✓a_✓m_✓e is supplied, the values of
                  the current options are printed.
          -t      Exit after reading and executing one command.
          -u      Treat unset variables as an error when



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                  performing parameter expansion.  If expansion
                  is attempted on an unset variable, the shell
                  prints an error message, and, if not interac-
                  tive, exits with a non-zero status.
          -v      Print shell input lines as they are read.
          -x      After expanding each _✓s_✓i_✓m_✓p_✓l_✓e-_✓c_✓o_✓m_✓m_✓a_✓n_✓d, bash
                  displays the expanded value of PS4, followed by
                  the command and its expanded arguments.
          -l      Save and restore the binding of _✓n_✓a_✓m_✓e in a for
                  _✓n_✓a_✓m_✓e [in word] command (see SHELL GRAMMAR
                  above).
          -d      Disable the hashing of commands that are looked
                  up for execution.  Normally, commands are
                  remembered in a hash table, and once found, do
                  not have to be looked up again.
          -C      The effect is as if the shell command
                  `noclobber=' had been executed (see Shell Vari-
                  ables above).
          -H      Enable ! style history substitution.  This flag
                  is on by by default.
          --      If no arguments follow this flag, then the
                  positional parameters are unset.  Otherwise,
                  the positional parameters are set to the _✓a_✓r_✓gs,
                  even if some of them begin with a -.
          -       Signal the end of options, cause all remaining
                  _✓a_✓r_✓gs to be assigned to the positional parame-
                  ters.  The -x and -v options are turned off.
                  If there are no _✓a_✓r_✓gs, the positional parameters
                  remain unchanged.

          Using + rather than - causes these flags to be turned
          off.  The flags can also be specified as options to an
          invocation of the shell.  The current set of flags may
          be found in $-.  After the option arguments are pro-
          cessed, the remaining _✓a_✓r_✓gs are treated as values for
          the positional parameters and are assigned, in order,
          to $1, $2, ... $9.  If no options or _✓a_✓r_✓gs are supplied,
          all shell variables are printed.  The return status is
          always true unless an illegal option is encountered.

     shift [_✓n]
          The positional parameters from _✓n+1 ... are renamed to
          $1 .... If _✓n is not given, it is assumed to be 1.  The
          exit status is 1 if _✓n is greater than $#; otherwise 0.

     suspend [-f]
          Suspend the execution of this shell until it receives a
          SIGCONT signal.  The -f option says not to complain if
          this is a login shell; just suspend anyway.

     test _✓e_✓x_✓p_✓r
     [ _✓e_✓x_✓p_✓r ]



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          Return a status of 0 (true) or 1 (false) depending on
          the evaluation of the conditional expression _✓e_✓x_✓p_✓r.
          Expressions may be unary or binary.  Unary expressions
          are often used to examine the status of a file.  There
          are string operators and numeric comparison operators
          as well.
          -b _✓f_✓i_✓l_✓e
               True if _✓f_✓i_✓l_✓e exists and is block special.
          -c _✓f_✓i_✓l_✓e
               True if _✓f_✓i_✓l_✓e exists and is character special.
          -d _✓f_✓i_✓l_✓e
               True if _✓f_✓i_✓l_✓e exists and is a directory.
          -e _✓f_✓i_✓l_✓e
               True if _✓f_✓i_✓l_✓e exists
          -f _✓f_✓i_✓l_✓e
               True if _✓f_✓i_✓l_✓e exists and is a regular file.
          -g _✓f_✓i_✓l_✓e
               True if _✓f_✓i_✓l_✓e exists and is set-group-id.
          -k _✓f_✓i_✓l_✓e
               True if _✓f_✓i_✓l_✓e has its ``sticky'' bit set.
          -L _✓f_✓i_✓l_✓e
               True if _✓f_✓i_✓l_✓e exists and is a symbolic link.
          -p _✓f_✓i_✓l_✓e
               True if _✓f_✓i_✓l_✓e exists and is a named pipe.
          -r _✓f_✓i_✓l_✓e
               True if _✓f_✓i_✓l_✓e exists and is readable.
          -s _✓f_✓i_✓l_✓e
               True if _✓f_✓i_✓l_✓e exists and has a size greater than
               zero.
          -S _✓f_✓i_✓l_✓e
               True if _✓f_✓i_✓l_✓e exists and is a socket.
          -t [_✓f_✓d]
               True if _✓f_✓d is opened on a terminal.  If _✓f_✓d is
               omitted, it defaults to 1 (standard output).
          -u _✓f_✓i_✓l_✓e
               True if _✓f_✓i_✓l_✓e exists and its set-user-id bit is
               set.
          -w _✓f_✓i_✓l_✓e
               True if _✓f_✓i_✓l_✓e exists and is writable.
          -x _✓f_✓i_✓l_✓e
               True if _✓f_✓i_✓l_✓e exists and is executable.
          -O _✓f_✓i_✓l_✓e
               True if _✓f_✓i_✓l_✓e exists and is owned by the effective
               user id.
          -G _✓f_✓i_✓l_✓e
               True if _✓f_✓i_✓l_✓e exists and is owned by the effective
               group id.
          _✓f_✓i_✓l_✓e_✓1 -nt _✓f_✓i_✓l_✓e_✓2
               True if _✓f_✓i_✓l_✓e_✓1 is newer (according to modification
               date) than _✓f_✓i_✓l_✓e_✓2.
          _✓f_✓i_✓l_✓e_✓1 -ot _✓f_✓i_✓l_✓e_✓2
               True if _✓f_✓i_✓l_✓e_✓1 is older than file2.



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          _✓f_✓i_✓l_✓e_✓1 -ef _✓f_✓i_✓l_✓e
               True if _✓f_✓i_✓l_✓e_✓1 and _✓f_✓i_✓l_✓e_✓2 have the same device and
               inode numbers.
          -z _✓s_✓t_✓r_✓i_✓n_✓g
               True if the length of _✓s_✓t_✓r_✓i_✓n_✓g is zero.
          -n _✓s_✓t_✓r_✓i_✓n_✓g
          _✓s_✓t_✓r_✓i_✓n_✓g
               True if the length of _✓s_✓t_✓r_✓i_✓n_✓g is non-zero.
          _✓s_✓t_✓r_✓i_✓n_✓g_✓1 = _✓s_✓t_✓r_✓i_✓n_✓g_✓2
               True if the strings are equal.
          _✓s_✓t_✓r_✓i_✓n_✓g_✓1 != _✓s_✓t_✓r_✓i_✓n_✓g_✓2
               True if the strings are not equal.
          ! _✓e_✓x_✓p_✓r
               True if _✓e_✓x_✓p_✓r is false.
          _✓e_✓x_✓p_✓r_✓1 -a _✓e_✓x_✓p_✓r_✓2
               True if both _✓e_✓x_✓p_✓r_✓1 AND _✓e_✓x_✓p_✓r_✓2 are true.
          _✓e_✓x_✓p_✓r_✓1 -o _✓e_✓x_✓p_✓r_✓2
               True if either _✓e_✓x_✓p_✓r_✓1 OR _✓e_✓x_✓p_✓r_✓2 is true.
          _✓a_✓r_✓g_✓1 OP _✓a_✓r_✓g_✓2
               OP is one of -eq, -ne, -lt, -le, -gt, or -ge.
               These arithmetic binary operators return true if
               _✓a_✓r_✓g_✓1 is equal, not-equal, less-than, less-than-
               or-equal, greater-than, or greater-than-or-equal
               than _✓a_✓r_✓g_✓2, respectively.  _✓A_✓r_✓g_✓1 and _✓a_✓r_✓g_✓2 may be
               positive integers, negative integers, or the spe-
               cial expression -l _✓s_✓t_✓r_✓i_✓n_✓g, which evaluates to the
               length of _✓s_✓t_✓r_✓i_✓n_✓g.

     times
          Print the accumulated user and system times for the
          shell and for processes run from the shell.

     trap [_✓a_✓r_✓g] [_✓s_✓i_✓g_✓s_✓p_✓e_✓c]
          The command _✓a_✓r_✓g is to be read and executed when the
          shell receives signal(s) _✓s_✓i_✓g_✓s_✓p_✓e_✓c.  If _✓a_✓r_✓g is absent or
          -, all specified signals are are reset to their origi-
          nal values (the values they had upon entrance to the
          shell).  If _✓a_✓r_✓g is the null string this signal is
          ignored by the shell and by the commands it invokes.
          _✓s_✓i_✓g_✓s_✓p_✓e_✓c is either a signal name in <signal.h>, or a
          signal number. If _✓s_✓i_✓g_✓s_✓p_✓e_✓c is EXIT (0) the command _✓a_✓r_✓g
          is executed on exit from the shell.  With no arguments,
          trap prints the list of commands associated with each
          signal number.  The -l option causes the shell to print
          a list of signal names and their corresponding numbers.
          An argument of -- disables option checking for the rest
          of the arguments.  Signals ignored upon entry to the
          shell cannot be trapped or reset.  Trapped signals are
          reset to their original values in a child process when
          it is created.  The return status is false if either
          then trap name or number is invalid; otherwise trap
          returns true.



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     type [-all] [-type | -path] [_✓n_✓a_✓m_✓e ...]
          With no options, indicate how each _✓n_✓a_✓m_✓e would be inter-
          preted if used as a command name.  If the -type flag is
          used, type prints a phrase which is one of _✓a_✓l_✓i_✓a_✓s, _✓k_✓e_✓y_✓-
          _✓w_✓o_✓r_✓d, _✓f_✓u_✓n_✓c_✓t_✓i_✓o_✓n, _✓b_✓u_✓i_✓l_✓t_✓i_✓n, or _✓f_✓i_✓l_✓e if _✓n_✓a_✓m_✓e 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 -path flag is used, type either returns the name of
          the disk file that would be executed if _✓n_✓a_✓m_✓e were
          specified as a command name, or nothing if -type would
          not return _✓f_✓i_✓l_✓e.  If a command is hashed, -path prints
          the hashed value, not necessarily the file that appears
          first in PATH.  If the -all flag is used, type prints
          all of the places that contain an executable named
          _✓n_✓a_✓m_✓e.  This includes aliases and functions, if and only
          if the -path flag is not also used.  The table of
          hashed commands is not consulted when using -all.  type
          accepts -a, -t, and -p in place of -all, -type, and
          -path, respectively.  An argument of -- disables option
          checking for the rest of the arguments.  type returns
          true if any of the arguments are found, false if none
          are found.

     ulimit [-SHacdfmstpn [_✓l_✓i_✓m_✓i_✓t]]
          Ulimit provides control over the resources available to
          the shell and to processes started by it, on systems
          that allow such control.  The value of _✓l_✓i_✓m_✓i_✓t can be a
          number in the unit specified for the resource, or the
          value unlimited.  The H and S options specify that the
          hard or soft limit is set for the given resource.  A
          hard limit cannot be increased 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, the command
          applies to the soft limit.  If _✓l_✓i_✓m_✓i_✓t 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 is
          printed before the value.  Other options are inter-
          preted as follows:
          -a   all current limits are reported
          -c   the maximum size of core files created
          -d   the maximum size of a process's data segment
          -f   the maximum size of files created by the shell
          -m   the maximum resident set size
          -s   the maximum stack size
          -t   the maximum amount of cpu time in seconds
          -p   the pipe size in 512-byte blocks (this may not be
               set)
          -n   the maximum number of open file descriptors (most
               systems do not allow this value to be set, only
               displayed)



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          An argument of -- disables option checking for the rest
          of the arguments.  If _✓l_✓i_✓m_✓i_✓t is given, it is the new
          value of the specified resource (the -a option is
          display only).  If no option is given, then -f is
          assumed.  Values are in 1024-byte increments, except
          for -t, which is in seconds, and -p, which is in units
          of 512-byte blocks.

     umask [-S] [_✓m_✓o_✓d_✓e]
          The user file-creation mask is set to _✓m_✓o_✓d_✓e.  If _✓m_✓o_✓d_✓e
          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 _✓c_✓h_✓m_✓o_✓d(_✓1).  If _✓m_✓o_✓d_✓e is
          omitted, or if the -S option is supplied, 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.  An argument of -- disables option
          checking for the rest of the arguments.

     unalias [_✓n_✓a_✓m_✓e ...]
          Remove _✓n_✓a_✓m_✓es from the list of defined aliases.  The
          return value is true unless _✓n_✓a_✓m_✓e is not a defined
          alias.

     unset [-fv] [_✓n_✓a_✓m_✓e ...]
          For each _✓n_✓a_✓m_✓e, remove the corresponding variable or,
          given the -f option, function.  An argument of -- dis-
          ables option checking for the rest of the arguments.
          Note that PATH, IFS, PPID, PS1, PS2, UID, and EUID can-
          not be unset.  If any of RANDOM, SECONDS, or LINENO are
          unset, they lose their special properties, even if they
          are subsequently reset.  The exit status is true unless
          the variable _✓n_✓a_✓m_✓e does not exist or is non-unsettable.

     wait [_✓n]
          Wait for the specified process and report its termina-
          tion status.  _✓n may be a process ID or a job specifica-
          tion; if a job spec is given, all processes in that
          job's pipeline are waited for.  If _✓n is not given, all
          currently active child processes are waited for, and
          the return code is zero.

INVOCATION
     A _✓l_✓o_✓g_✓i_✓n _✓s_✓h_✓e_✓l_✓l is one whose first character of argument zero
     is a - , or one started with the -login flag.

     An _✓i_✓n_✓t_✓e_✓r_✓a_✓c_✓t_✓i_✓v_✓e shell is one whose standard input and output
     are both connected to terminals (as determined by
     _✓i_✓s_✓a_✓t_✓t_✓y(3)), or one started with the -i flag.  PS1 is set and
     $- includes i if bash is interactive, allowing a way to test
     this state from a shell script or a startup file.




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     Login shells:
       On login:
             if /_✓e_✓t_✓c/_✓p_✓r_✓o_✓f_✓i_✓l_✓e exists, source it.

             if ~/._✓b_✓a_✓s_✓h__✓p_✓r_✓o_✓f_✓i_✓l_✓e exists, source it,
               else if ~/._✓b_✓a_✓s_✓h__✓l_✓o_✓g_✓i_✓n exists, source it,
                 else if ~/._✓p_✓r_✓o_✓f_✓i_✓l_✓e exists, source it.

       On logout:
             if ~/._✓b_✓a_✓s_✓h__✓l_✓o_✓g_✓o_✓u_✓t exists, source it.

     Non-login interactive shells:
       On startup:
             if ~/._✓b_✓a_✓s_✓h_✓r_✓c exists, source it.

     Non-interactive shells:
       On startup:
             if the environment variable ENV is non-null, expand
          it and source the file it names.

SEE ALSO
     _✓T_✓h_✓e _✓G_✓n_✓u _✓R_✓e_✓a_✓d_✓l_✓i_✓n_✓e _✓L_✓i_✓b_✓r_✓a_✓r_✓y, Brian Fox
     _✓T_✓h_✓e _✓G_✓n_✓u _✓H_✓i_✓s_✓t_✓o_✓r_✓y _✓L_✓i_✓b_✓r_✓a_✓r_✓y, Brian Fox
Lennert
     _✓A _✓S_✓y_✓s_✓t_✓e_✓m _✓V _✓C_✓o_✓m_✓p_✓a_✓t_✓i_✓b_✓l_✓e _✓I_✓m_✓p_✓l_✓e_✓m_✓e_✓n_✓t_✓a_✓t_✓i_✓o_✓n _✓o_✓f _✓4._✓2_✓B_✓S_✓D _✓J_✓o_✓b _✓C_✓o_✓n_✓t_✓r_✓o_✓l, David
     _✓H_✓o_✓w _✓t_✓o _✓w_✓e_✓a_✓r _✓w_✓e_✓i_✓r_✓d _✓p_✓a_✓n_✓t_✓s _✓f_✓o_✓r _✓f_✓u_✓n _✓a_✓n_✓d _✓p_✓r_✓o_✓f_✓i_✓t, Brian Fox
     _✓s_✓h(1), _✓k_✓s_✓h(1), _✓c_✓s_✓h(1)

FILES
     /_✓b_✓i_✓n/_✓b_✓a_✓s_✓h
          The bash executable
     /_✓e_✓t_✓c/_✓p_✓r_✓o_✓f_✓i_✓l_✓e
          The systemwide initialization file, executed for login
          shells
     ~/._✓b_✓a_✓s_✓h__✓p_✓r_✓o_✓f_✓i_✓l_✓e
          The personal initialization file, executed for login
          shells
     ~/._✓b_✓a_✓s_✓h_✓r_✓c
          The individual per-interactive-shell startup file
     ~/._✓i_✓n_✓p_✓u_✓t_✓r_✓c
          Individual _✓R_✓e_✓a_✓d_✓l_✓i_✓n_✓e initialization file

AUTHORS
          Brian Fox, Free Software Foundation (primary author)
          [e-mail]

          Chet Ramey, Case Western Reserve University
          [e-mail]

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



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BASH(1)                   1991 July 15                    BASH(1)



     appears in the latest version of bash that you have.

     Once you have determined that a bug actually exists, mail a
     bug report to _✓b_✓a_✓s_✓h-_✓m_✓a_✓i_✓n_✓t_✓a_✓i_✓n_✓e_✓r_✓s@_✓a_✓i._✓M_✓I_✓T._✓E_✓d_✓u.  If you have a
     fix, you are welcome to mail that as well!  Suggestions and
     `philosophical' bug reports may be mailed to _✓b_✓u_✓g-
     _✓b_✓a_✓s_✓h@_✓a_✓i._✓M_✓I_✓T._✓E_✓d_✓u 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

     Comments and bug reports concerning this manual page should
     be directed to _✓c_✓h_✓e_✓t@_✓i_✓n_✓s._✓C_✓W_✓R_✓U._✓E_✓d_✓u.

BUGS
     It's too big and too slow.

     There are some subtle differences between bash and tradi-
     tional versions of sh, mostly because of the POSIX specifi-
     cation.

     Aliases are confusing in some uses.



























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