sh

BASH(1)                      General Commands Manual                     BASH(1)



NAME
       bash - GNU Bourne-Again SHell

SYNOPSIS
       bash [options] [file]

COPYRIGHT
       Bash is 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 Korn and C shells (ksh and csh).

       Bash is ultimately intended to be a conformant implementation of the IEEE
       Posix Shell and Tools specification (IEEE Working Group 1003.2).

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

       -c string If the -c flag is present, then commands are read from string.
                 If there are arguments after the string, they are assigned to
                 the positional parameters, starting with $0.
       -i        If the -i flag is present, the shell is interactive.
       -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 read and execute the personal initialization file
                 ~/.bashrc if the shell is interactive.  This option is on by
                 default if the shell is invoked as sh.
       -noprofile
                 Do not read either the system-wide startup file /etc/profile or
                 any of the personal initialization files ~/.bash_profile,
                 ~/.bash_login, or ~/.profile.  By default, bash normally reads
                 these files when it is invoked as a login shell (see INVOCATION
                 below).
       -rcfile file
                 Execute commands from file instead of the standard personal
                 initialization file ~/.bashrc, if the shell is interactive (see
                 INVOCATION below).
       -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).  This is the default.
       -login    Make bash act as if it had been invoked as a login shell.
       -nobraceexpansion
                 Do not perform curly brace expansion (see Brace Expansion
                 below).
       -nolineediting
                 Do not use the GNU readline library to read command lines if
                 interactive.
       -posix    Change the behavior of bash where the default operation differs
                 from the Posix 1003.2 standard to match the standard

ARGUMENTS
       If arguments remain after option processing, and neither the -c nor the
       -s option has been supplied, the first argument is assumed to be the name
       of a file containing shell commands.  If bash is invoked in this fashion,
       $0 is set to the name of the file, and the positional parameters are set
       to the remaining arguments.  Bash reads and executes commands from this
       file, then exits.  Bash's exit status is the exit status of the last
       command executed in the script.

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 word consisting only of alphanumeric characters and underscores,
              and beginning with an alphabetic character or an underscore.  Also
              referred to as an identifier.
       metacharacter
              A character that, when unquoted, separates words.  One of the
              following:
              |  & ; ( ) < > space tab
       control operator
              A token that performs a control function.  It is one of the
              following symbols:
              || & && ; ;; ( ) | <newline>

RESERVED WORDS
       Reserved words are words that have a special meaning to the shell.  The
       following words are recognized as reserved when unquoted and either the
       first word of a simple command (see SHELL GRAMMAR below) or the third
       word of a case or for command:

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

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

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

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

              [ ! ] command [ | command2 ... ]

       The standard output of command is connected to the standard input of
       command2.  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 list is a sequence of one or more pipelines separated by one of the
       operators ;, &, &&, or ⎪⎪, and terminated by one of ;, &, or <newline>.

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

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

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

              command && command2

       command2 is executed if, and only if, command returns an exit status of
       zero.

       An OR list has the form

              command ⎪⎪ command2

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

   Compound Commands
       A compound command is one of the following:

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

       { list; }
              list is simply executed in the current shell environment.  This is
              known as a group command.  The return status is the exit status of
              list.

       for name [ in word; ] do list ; done
              The list of words following in is expanded, generating a list of
              items.  The variable name is set to each element of this list in
              turn, and list is executed each time.  If the in word is omitted,
              the for command executes list once for each positional parameter
              that is set (see PARAMETERS below).

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

       case word in [ pattern [ | pattern ] ... ) list ;; ] ... esac
              A case command first expands word, and tries to match it against
              each pattern in turn, using the same matching rules as for
              pathname expansion (see Pathname Expansion below).  When a match
              is found, the corresponding list is executed.  After the first
              match, no subsequent matches are attempted.  The exit status is
              zero if no patterns are matches.  Otherwise, it is the exit status
              of the last command executed in list.

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

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

       [ function ] name () { list; }
              This defines a function named name.  The body of the function is
              the list of commands between { and }.  This list is executed
              whenever name 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, or an interactive shell in which the -o
       interactive-comments option to the set builtin is enabled, a word
       beginning with # causes that word and all remaining characters on that
       line to be ignored.  An interactive shell without the -o
       interactive-comments option enabled does not allow comments.

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

       Each of the metacharacters listed above under DEFINITIONS has special
       meaning to the shell and must be quoted if they are to represent
       themselves.  There are three quoting mechanisms: the escape character,
       single quotes, and double quotes.

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

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

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

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

PARAMETERS
       A parameter is an entity that stores values, somewhat like a variable in
       a conventional programming language.  It can be a name, a number, or one
       of the special characters listed below under Special Parameters.  For the
       shell's purposes, a variable is a parameter denoted by a name.

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

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

              name=[value]

       If value is not given, the variable is assigned the null string.  All
       values undergo tilde expansion, parameter and variable expansion, command
       substitution, arithmetic expansion, and quote removal.  If the variable
       has its -i attribute set (see declare below in SHELL BUILTIN COMMANDS)
       then value 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 positional parameter is a parameter denoted by one or more digits,
       other than the single digit 0.  Positional parameters are assigned from
       the shell's arguments when it is invoked, and may be reassigned using the
       set builtin command.  Positional parameters may not be assigned to with
       assignment statements.  The positional parameters are temporarily
       replaced when a shell function is executed (see FUNCTIONS below).

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

   Special Parameters
       The shell treats several parameters specially.  These parameters may only
       be referenced; assignment to them is not allowed.
       *      Expands to the positional parameters, starting from one.  When the
              expansion occurs within double quotes, it expands to a single word
              with the value of each parameter separated by the first character
              of the IFS special variable.  That is, ``$*'' is equivalent to
              ``$1c$2c...'', where c is the first character of the value of the
              IFS variable.  If IFS is 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 nothing (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 () subshell, 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.  If bash is started with the
              -c option, then $0 is set to the first argument after the string
              to be executed, if one is present.  Otherwise, it is set to the
              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 command.
       REPLY  Set to the line of input read by the read builtin command when no
              arguments are supplied.
       UID    Expands to the user ID of the current user, initialized at shell
              startup.
       EUID   Expands to the effective user ID of the current user, initialized
              at shell startup.
       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 subsequent references is the
              number of seconds since the assignment plus the value assigned.
              If SECONDS is unset, it loses its special properties, even if it
              is subsequently reset.
       LINENO Each time this parameter is referenced, the shell substitutes a
              decimal number representing the current sequential line number
              (starting with 1) within a script or function.  When not in a
              script or function, the value substituted is not guaranteed to be
              meaningful.  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 simple commands executed in the
              current function.  If LINENO is unset, it loses its special
              properties, even if it is subsequently reset.
       HISTCMD
              The history number, or index in the history list, of the current
              command.  If HISTCMD is unset, it loses its special properties,
              even if it is subsequently reset.
       OPTARG The value of the last option argument processed by the getopts
              builtin command (see SHELL BUILTIN COMMANDS below).
       OPTIND The index of the next argument to be processed by the getopts
              builtin command (see SHELL BUILTIN COMMANDS below).
       HOSTTYPE
              Automatically set to a string that uniquely describes the type of
              machine on which bash is executing.  The default is system-
              dependent.
       OSTYPE Automatically set to a string that describes the operating system
              on which bash is executing.  The default is system-dependent.

       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 Internal Field Separator that is used for word splitting after
              expansion and to split lines into words with the read builtin
              command.  The default value is ``<space><tab><newline>''.
       PATH   The search path for commands.  It is a colon-separated list of
              directories in which the shell looks for commands (see COMMAND
              EXECUTION below).  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:.''.
       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 command.  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 containing commands to
              initialize the shell, as in .bashrc.  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 `?'.  $_ stands for the name of the
              current mailfile.  Example:
              MAILPATH='/usr/spool/mail/bfox?"You have mail":~/shell-mail?"$_
              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 mailfile 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 and used as the secondary
              prompt string.  The default is ``> ''.
       PS3    The value of this parameter is used as the prompt for the select
              command (see SHELL GRAMMAR above).
       PS4    The value of this parameter is expanded 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 ``+
              ''.
       HISTSIZE
              The number of commands to remember in the command history (see
              HISTORY below).  The default value is 500.
       HISTFILE
              The name of the file in which command history is saved.  (See
              HISTORY below.)  The default value is ~/.bash_history.  If unset,
              the command history is not saved when an interactive shell exits.
       HISTFILESIZE
              The maximum number of lines contained in the history file.  When
              this variable is assigned a value, the history file is truncated,
              if necessary, to contain no more than that number of lines.  The
              default value is 500.
       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
              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 as the first characters on an input line
              before bash exits.  If the variable exists but does not have a
              numeric value, or has no value, the default value is 10.  If it
              does not exist, EOF signifies the end of input to the shell.  This
              is only in effect for interactive shells.
       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
              A colon-separated list of suffixes to ignore when performing
              filename completion (see READLINE below).  A filename whose suffix
              matches one of the entries in FIGNORE is excluded from the list of
              matched filenames.  A sample value is ``.o:~''.
       INPUTRC
              The filename for the readline startup file, overriding the default
              of ~/.inputrc (see READLINE below).
       notify If set, bash reports terminated background jobs immediately,
              rather than waiting until before printing the next primary prompt
              (see also the -b option to the set builtin command).
       history_control
       HISTCONTROL
              If set to a value of ignorespace, lines which begin with a space
              character are not entered on the history list.  If set to a value
              of ignoredups, lines matching the last history line are not
              entered.  A value of ignoreboth combines the two options.  If
              unset, or if set to any other value than those above, all lines
              read by the parser are saved on the history list.

       command_oriented_history
              If set, bash attempts to save all lines of a multiple-line command
              in the same history entry.  This allows easy re-editing of
              multi-line commands.

       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 or three characters which control history expansion and
              tokenization (see HISTORY EXPANSION below).  The first character
              is the history expansion character, that is, the character which
              signals the start of a history expansion, normally `!'.  The
              second character is the quick substitution character, which is
              used as shorthand for re-running the previous command entered,
              substituting one string for another in the command.  The default
              is `^'.  The optional third character is the character which
              signifies that the remainder of the line is a comment, when found
              as the first character of a word, normally `#'.  The history
              comment character causes history substitution to be skipped for
              the remaining words on the line.  It does not necessarily cause
              the shell parser to treat the rest of the line as a comment.

       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 which
              change the current directory, such as cd.  See also the
              description of the -P option to the set builtin ( SHELL BUILTIN
              COMMANDS below).
       hostname_completion_file
       HOSTFILE
              Contains the name of a file in the same format as /etc/hosts that
              should be read when the shell needs to complete a hostname.  The
              file may be changed interactively; the next time hostname
              completion is attempted 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 user and
              job control.  If this variable is set, single word simple commands
              without redirections are treated as candidates for resumption of
              an existing stopped job.  There is no ambiguity allowed; if there
              is more than one job beginning with the string typed, the job most
              recently accessed is selected.  The name of a stopped job, in this
              context, is the command line used to start it.  If set to the
              value exact, the string supplied must match the name of a stopped
              job exactly; if set to substring, the string supplied needs to
              match a substring of the name of a stopped job.  The substring
              value provides functionality analogous to the %?  job id (see JOB
              CONTROL below).  If set to any other value, the supplied string
              must be a prefix of a stopped job's name; this provides
              functionality analogous to the % job id.

       no_exit_on_failed_exec
              If this variable exists, a non-interactive shell will not exit if
              it cannot execute the file specified in the exec builtin command.
              An interactive shell does not exit if exec fails.

       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.

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

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

       On systems that can support it, there is an additional expansion
       available: process substitution.

       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 single exception to this is the expansion of
       ``$@'' as explained above (see PARAMETERS).

   Brace Expansion
       Brace expansion is a mechanism by which arbitrary strings may be
       generated.  This mechanism is similar to pathname expansion, but the
       filenames generated need not exist.  Patterns to be brace expanded take
       the form of an optional preamble, followed by a series of comma-separated
       strings between a pair of braces, followed by an optional postamble.  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.  It
       is strictly textual.  Bash does not apply any syntactic interpretation to
       the context of the expansion or the text between the braces.

       A correctly-formed brace expansion must contain unquoted opening and
       closing braces, and at least one unquoted comma.  Any incorrectly formed
       brace expansion is left unchanged.

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

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

       Brace expansion introduces a slight incompatibility with 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
       expansion.  For example, a word entered to sh as file{1,2} appears
       identically in the output.  The same word is output as file1 file2 after
       expansion by bash.  If strict compatibility with sh is desired, start
       bash with the -nobraceexpansion 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 login name. If this login name 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 substituted
       instead.

       If a `+' follows the tilde, the value of PWD replaces the tilde and `+'.
       If a `-' follows, the value of OLDPWD is substituted.  If the value
       following the tilde is a valid login name, the tilde and login name are
       replaced with the home directory associated with that name.  If the name
       is invalid, or the tilde expansion fails, the word is unchanged.

       Each variable assignment is checked for unquoted instances of tildes
       following a : or =.  In these cases, tilde substitution is also
       performed.  Consequently, one may use pathnames with tildes in
       assignments to PATH, MAILPATH, and CDPATH, and the shell assigns the
       expanded value.

   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.

       ${parameter}
              The value of parameter is substituted.  The braces are required
              when parameter is a positional parameter with more than one digit,
              or when parameter is followed by a character which is not to be
              interpreted as part of its name.

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

       ${parameter:-word}
              Use Default Values.  If parameter is unset or null, the expansion
              of word is substituted.  Otherwise, the value of parameter is
              substituted.
       ${parameter:=word}
              Assign Default Values.  If parameter is unset or null, the
              expansion of word is assigned to parameter.  The value of
              parameter is then substituted.  Positional parameters and special
              parameters may not be assigned to in this way.
       ${parameter:?word}
              Display Error if Null or Unset.  If parameter is null or unset,
              the expansion of word (or a message to that effect if word is not
              present) is written to the standard error and the shell, if it is
              not interactive, exits.  Otherwise, the value of parameter is
              substituted.
       ${parameter:+word}
              Use Alternate Value.  If parameter is null or unset, nothing is
              substituted, otherwise the expansion of word is substituted.
       ${#parameter}
              The length in characters of the value of parameter is substituted.
              If parameter is * or @, the length substituted is the length of *
              expanded within double quotes.
       ${parameter#word}
       ${parameter##word}
              The word is expanded to produce a pattern just as in pathname
              expansion.  If the pattern matches the beginning of the value of
              parameter, then the expansion is the value of parameter with the
              shortest matching pattern deleted (the ``#'' case) or the longest
              matching pattern deleted (the ``##'' case).

       ${parameter%word}
       ${parameter%%word}
              The word is expanded to produce a pattern just as in pathname
              expansion.  If the pattern matches a trailing portion of the value
              of parameter, then the expansion is the value of parameter with
              the shortest matching pattern deleted (the ``%'' case) or the
              longest matching pattern deleted (the ``%%'' case).

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

              $(command)
       or
              `command`

       Bash performs the expansion by executing command and replacing 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 $(command) form, all characters between the parentheses make up
       the command; none are treated specially.

       Command substitutions may be nested.  To nest when using the 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.  There are two formats for arithmetic
       expansion:

              $[expression]

              $((expression))

       The expression is treated as if it were within double quotes, but a
       double quote inside the braces or parentheses is not treated specially.
       All tokens in the expression undergo parameter expansion, command
       substitution, and quote removal.  Arithmetic substitutions may be nested.

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

   Process Substitution
       Process substitution is supported on systems that support named pipes
       (FIFOs) or the /dev/fd method of naming open files.  It takes the form of
       <(list) or >(list).  The process list is run with its input or output
       connected to a FIFO or some file in /dev/fd.  The name of this file is
       passed as an argument to the current command as the result of the
       expansion.  If the >(list) form is used, writing to the file will provide
       input for list.  If the <(list) form is used, the file passed as an
       argument should be read to obtain the output of list.

       On systems that support it, process substitution is performed
       simultaneously with parameter and variable expansion, command
       substitution, and arithmetic expansion.

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

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

       Explicit null arguments ("" or '') are retained.  Implicit null
       arguments, resulting from the expansion of parameters that have no
       values, are removed.

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

   Pathname Expansion
       After word splitting, unless the -f option has been set, bash scans each
       word for the characters *, ?, and [.  If one of these characters appears,
       then the word is regarded as a pattern, and replaced with an
       alphabetically sorted list of 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, and no matches are found, the word is removed.  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 range; any character lexically
              between those two characters, inclusive, is matched.  If the first
              character following 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 redirected
       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 precede or appear
       anywhere within a simple command or may follow a command.  Redirections
       are processed in the order they appear, from left to right.

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

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

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

              ls > dirlist 2>&1

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

              ls 2>&1 > dirlist

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

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

       The general format for redirecting input is:

              [n]<word

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

       The general format for redirecting output is:

              [n]>word

       If the redirection operator is >|, then the value of the -C option to the
       set builtin command is not tested, and file creation is attempted.  (See
       also the description of noclobber under Shell Variables above.)

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

       The general format for appending output is:

              [n]>>word

   Redirecting Standard Output and Standard Error
       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 word with this construct.

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

              &>word
       and
              >&word

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

              >word 2>&1

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

       The format of here-documents is as follows:

              <<[-]word
                      here-document
              delimiter

       No parameter expansion, command substitution, pathname expansion, or
       arithmetic expansion is performed on word.  If any characters in word are
       quoted, the delimiter is the result of quote removal on word, 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 containing delimiter.  This allows
       here-documents within shell scripts to be indented in a natural fashion.

   Duplicating File Descriptors
       The redirection operator

              [n]<&word

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

       The operator

              [n]>&word

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

   Opening File Descriptors for Reading and Writing
       The redirection operator

              [n]<>word

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

FUNCTIONS
       A shell function, defined as described above under SHELL GRAMMAR, stores
       a series of commands for later execution.  Functions are executed in the
       context of the current shell; no new process is created to interpret them
       (contrast this with the execution of a shell script).  When a function is
       executed, the arguments to the function become the positional parameters
       during its execution.  The special parameter # is updated to reflect the
       change.  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 command 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 and definitions 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 aliases that may be set and unset with the
       alias and unalias builtin commands (see SHELL BUILTIN COMMANDS below).
       The first word of each command, if unquoted, is checked to see if it has
       an alias.  If so, that word is replaced by the text of the alias.  The
       alias name and the replacement text may contain any valid shell input,
       including the metacharacters listed above, with the exception that the
       alias name may not contain =.  The first word of the replacement text is
       tested for aliases, but a word that is identical to an alias being
       expanded is not expanded a second time.  This means that one may alias ls
       to ls -F, for instance, and bash does not try to recursively expand the
       replacement text.  If the last character of the alias value is a blank,
       then the next command word following the alias is also checked for alias
       expansion.

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

       There is no mechanism for using arguments in the replacement text, as in
       csh.  If arguments are needed, a shell function should be used.

       Aliases are not expanded when the shell is not interactive.

       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 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 commands following
       the alias definition on that line are not affected by the new alias.
       This behavior is also an issue when functions are executed.  Aliases are
       expanded when the function definition is read, not when the function is
       executed, 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.

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

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

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

              [1] 25647

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

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

       If the operating system on which bash is running supports job control,
       bash allows you to use it.  Typing the suspend character (typically ^Z,
       Control-Z) while a process is running causes that process to be stopped
       and returns you to bash.  Typing the delayed suspend character (typically
       ^Y, Control-Y) causes the process to be stopped when it attempts to read
       input from the terminal, and control to be returned to bash.  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, refers to any job
       containing the string ce in its command line.  If the substring matches
       more than one job, bash reports an error.  The symbols %% and %+ refer to
       the shell's notion of the current job, which is the last job stopped
       while it was in the foreground.  The previous job 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 foreground: %1 is a
       synonym for ``fg %1'', bringing job 1 from the background into the
       foreground.  Similarly, ``%1 &'' resumes job 1 in the background,
       equivalent to ``bg %1''.

       The shell learns immediately whenever a job changes state.  Normally,
       bash waits until it is about to print a prompt before reporting changes
       in a job's status so as to not interrupt any other output.  If the -b
       option to the set builtin command is set, bash reports such changes
       immediately.  (See also the description of notify variable under Shell
       Variables above.)

       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 the
       wait builtin is interruptible).  In all cases, 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.  When job control is not in effect,
       background jobs (jobs started with &) ignore SIGINT and SIGQUIT.
       Commands 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 following actions are
       taken.

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

       If the name is neither a shell function nor a builtin, and contains no
       slashes, bash searches each element of the PATH for a directory
       containing an executable file by that name.  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 arguments to the command are set to the
       arguments given, if any.

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

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

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

       The shell 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 export to child
       processes.  Executed commands inherit the environment.  The export and
       declare -x commands allow parameters and functions to be added to and
       deleted from the environment.  If the value of a parameter in the
       environment is modified, the new value becomes part of the environment,
       replacing the old.  The environment inherited by any executed command
       consists of the shell's initial environment, whose values may be modified
       in the shell, less any pairs removed by the unset command, plus any
       additions via the export and declare -x commands.

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

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

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

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.

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

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

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 these prompt strings to be
       customized by inserting a number of backslash-escaped special characters
       that are decoded as follows:
              \t     the current time in HH:MM:SS format
              \d     the date in "Weekday Month Date" format (e.g., "Tue May
                     26")
              \n     newline
              \s     the name of the shell, the basename of $0 (the 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   the character corresponding to the octal number nnn
              \\     a backslash
              \[     begin a sequence of non-printing characters, which could be
                     used to embed a terminal control sequence into the prompt
              \]     end a sequence of non-printing characters

       The command number and the history number are usually different: the
       history number of a command is its position in the history list, which
       may include commands restored from the history file (see HISTORY below),
       while the command number is the position in the sequence of commands
       executed during the current shell session.  After the string is decoded,
       it is expanded via parameter expansion, command substitution, arithmetic
       expansion, and 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-key, e.g., C-n means Control-N.  Similarly,
       meta keys are denoted by M-key, so M-x means Meta-X.  (On keyboards
       without a meta key, M-x means ESC x, i.e., press the Escape key then the
       x key.  This makes ESC the meta prefix.  The combination M-C-x means
       ESC-Control-x, or press the Escape key then hold the Control key while
       pressing the x key.)

       The default key-bindings may be changed with an ~/.inputrc file.  The
       value of the shell variable INPUTRC, if set, is used instead of
       ~/.inputrc.  Other programs that use this library may add their own
       commands and bindings.

       For example, placing

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

       The following symbolic character names are recognized: RUBOUT, DEL, ESC,
       LFD, NEWLINE, RET, RETURN, SPC, SPACE, and TAB.  In addition to command
       names, readline allows keys to be bound to a string that is inserted when
       the key is pressed (a macro).

       Readline is customized by putting commands in an initialization file.
       The name of this file is taken from the value of the INPUTRC variable.
       If that variable is unset, the default is ~/.inputrc.  When a program
       which uses the readline library starts up, the init file is read, and the
       key bindings and variables are set.  There are only a few basic
       constructs allowed in the readline init file.  Blank lines are ignored.
       Lines beginning with a # are comments.  Lines beginning with a $ indicate
       conditional constructs.  Other lines denote key bindings and variable
       settings.

       The syntax for controlling key bindings in the ~/.inputrc file is simple.
       All that is required is the name of the command or the text of a macro
       and a key sequence to which it should be bound. The name may be specified
       in one of two ways: as a symbolic key name, possibly with Meta- or
       Control- prefixes, or as a key sequence.  When using the form
       keyname:function-name or macro, keyname is the name of a key spelled out
       in English.  For example:

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

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

       In the second form, "keyseq":function-name or macro, keyseq differs from
       keyname above in that strings denoting an entire key sequence may be
       specified by placing the sequence within double quotes.  Some GNU Emacs
       style key escapes can be used, as in the following example.

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

       In this example, C-u is again bound to the function universal-argument.
       C-x C-r is bound to the function re-read-init-file, and ESC [ 1 1 ~ is
       bound to insert the text Function Key 1.  The full set of escape
       sequences is

              \C-    control prefix

              \M-    meta prefix

              \e     an escape character

              \\     backslash

              \"     literal "

              \'     literal '

       When entering the text of a macro, single or double quotes should be used
       to indicate a macro definition.  Unquoted text is assumed to be a
       function name.  Backslash will quote any character in the macro text,
       including " and '.

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

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

              set variable-name value

       Except where noted, readline variables can take the values On or Off.
       The variables and their default values are:

       horizontal-scroll-mode (Off)
              When set to On, makes readline use a single line for display,
              scrolling the input horizontally on a single screen line when it
              becomes longer than the screen width rather than wrapping to a new
              line.
       editing-mode (emacs)
              Controls whether readline begins with a set of key bindings
              similar to emacs or vi.  editing-mode can be set to either emacs
              or vi.
       mark-modified-lines (Off)
              If set to On, history lines that have been modified are displayed
              with a preceding asterisk (*).
       bell-style (audible)
              Controls what happens when readline wants to ring the terminal
              bell.  If set to none, readline never rings the bell.  If set to
              visible, readline uses a visible bell if one is available.  If set
              to audible, readline attempts to ring the terminal's bell.
       comment-begin (``#'')
              The string that is inserted in vi mode when the vi-comment command
              is executed.
       meta-flag (Off)
              If set to On, readline will enable eight-bit input (that is, it
              will not strip the high bit from the characters it reads),
              regardless of what the terminal claims it can support.
       convert-meta (On)
              If set to On, readline will convert characters with the eighth bit
              set to an ASCII key sequence by stripping the eighth bit and
              prepending an escape character (in effect, using escape as the
              meta prefix).
       output-meta (Off)
              If set to On, readline will display characters with the eighth bit
              set directly rather than as a meta-prefixed escape sequence.
       completion-query-items (100)
              This determines when the user is queried about viewing the number
              of possible completions generated by the possible-completions
              command.  It may be set to any integer value greater than or equal
              to zero.  If the number of possible completions is greater than or
              equal to the value of this variable, the user is asked whether or
              not he wishes to view them; otherwise they are simply listed on
              the terminal.
       keymap (emacs)
              Set the current readline keymap.  The set of legal keymap names is
              emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move, vi-
              command, and vi-insert.  vi is equivalent to vi-command; emacs is
              equivalent to emacs-standard.  The default value is emacs; the
              value of editing-mode also affects the default keymap.
       show-all-if-ambiguous (Off)
              This alters the default behavior of the completion functions.  If
              set to on, words which have more than one possible completion
              cause the matches to be listed immediately instead of ringing the
              bell.
       expand-tilde (Off)
              If set to on, tilde expansion is performed when readline attempts
              word completion.

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

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

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

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

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

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

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

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

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

       The following is a list of the names of the commands and the default key
       sequences to which they are bound.

   Commands for Moving
       beginning-of-line (C-a)
              Move to the start of the current line.
       end-of-line (C-e)
              Move to the end of the line.
       forward-char (C-f)
              Move forward a character.
       backward-char (C-b)
              Move back a character.
       forward-word (M-f)
              Move forward to the end of the next word.  Words are composed of
              alphanumeric characters (letters and digits).
       backward-word (M-b)
              Move back to the start of this, or the previous, word.  Words are
              composed of alphanumeric characters (letters and digits).
       clear-screen (C-l)
              Clear the screen leaving the current line at the top of the
              screen.  With an argument, refresh the current line without
              clearing the screen.
       redraw-current-line
              Refresh the current line.  By default, this is unbound.

   Commands for Manipulating the History
       accept-line (Newline, Return)
              Accept the line regardless of where the cursor is.  If this line
              is non-empty, add it to the history list according to the state of
              the HISTCONTROL variable.  If the line is a modified history line,
              then restore the history line to its original state.
       previous-history (C-p)
              Fetch the previous command from the history list, moving back in
              the list.
       next-history (C-n)
              Fetch the next command from the history list, moving forward in
              the list.
       beginning-of-history (M-<)
              Move to the first line in the history.
       end-of-history (M->)
              Move to the end of the input history, i.e., the line currently
              being entered.
       reverse-search-history (C-r)
              Search backward starting at the current line and moving `up'
              through the history as necessary.  This is an incremental search.
       forward-search-history (C-s)
              Search forward starting at the current line and moving `down'
              through the history as necessary.  This is an incremental search.
       non-incremental-reverse-search-history (M-p)
              Search backward through the history starting at the current line
              using a non-incremental search for a string supplied by the user.
       non-incremental-forward-search-history (M-n)
              Search forward through the history using a non-incremental search
              for a string supplied by the user.
       history-search-forward
              Search forward through the history for the string of characters
              between the start of the current line and the current point.  This
              is a non-incremental search.  By default, this command is unbound.
       history-search-backward
              Search backward through the history for the string of characters
              between the start of the current line and the current point.  This
              is a non-incremental search.  By default, this command is unbound.
       yank-nth-arg (M-C-y)
              Insert the first argument to the previous command (usually the
              second word on the previous line) at point (the current cursor
              position).  With an argument n, insert the nth word from the
              previous command (the words in the previous command begin with
              word 0).  A negative argument inserts the nth word from the end of
              the previous command.
       yank-last-arg (M-., M-_)
              Insert the last argument to the previous command (the last word on
              the previous line).  With an argument, behave exactly like yank-
              nth-arg.
       shell-expand-line (M-C-e)
              Expand the line the way the shell does when it reads it.  This
              performs alias and history expansion as well as all of the shell
              word expansions.  See HISTORY EXPANSION below for a description of
              history expansion.
       history-expand-line (M-^)
              Perform history expansion on the current line.  See HISTORY
              EXPANSION below for a description of history expansion.
       insert-last-argument (M-., M-_)
              A synonym for yank-last-arg.
       operate-and-get-next (C-o)
              Accept the current line for execution and fetch the next line
              relative to the current line from the history for editing.  Any
              argument is ignored.

   Commands for Changing Text
       delete-char (C-d)
              Delete the character under the cursor.  If point is at the
              beginning of the line, there are no characters 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.  When given a numeric
              argument, save the deleted text on the kill-ring.
       quoted-insert (C-q, C-v)
              Add the next character that you type to the line verbatim.  This
              is how to insert characters like C-q, for example.
       tab-insert (C-v TAB)
              Insert a tab character.
       self-insert (a, b, A, 1, !, ...)
              Insert the character typed.
       transpose-chars (C-t)
              Drag the character before point forward over the character at
              point.  Point moves forward as well.  If point is at the end of
              the line, then transpose the two characters 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)
              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.
       backward-kill-line (C-x C-Rubout)
              Kill backward to the beginning of the line.
       unix-line-discard (C-u)
              Kill backward from point to the beginning of the line.
       kill-whole-line
              Kill all characters on the current line, no matter where the
              cursor is.  By default, this is unbound.
       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.  Word boundaries are the same
              as those used by forward-word.
       backward-kill-word (M-Rubout)
              Kill the word behind the cursor.  Word boundaries are the same as
              those used by backward-word.
       unix-word-rubout (C-w)
              Kill the word behind the cursor, using white space as a word
              boundary.  The word boundaries are different from
              backward-kill-word.
       delete-horizontal-space
              Delete all spaces and tabs around point.  By default, this is
              unbound.
       yank (C-y)
              Yank the top of the kill ring into the buffer at the cursor.
       yank-pop (M-y)
              Rotate the kill-ring, and yank the new top.  Only works following
              yank or yank-pop.

   Numeric Arguments
       digit-argument (M-0, M-1, ..., M--)
              Add this digit to the argument already accumulating, or start a
              new argument.  M-- starts a negative argument.
       universal-argument
              Each time this is executed, the argument count is multiplied by
              four.  The argument count is initially one, so executing this
              function the first time makes the argument count four.  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 variable (if the text
              begins with $), username (if the text begins with ~), hostname (if
              the text begins with @), or command (including aliases and
              functions) in turn.  If none of these produces a match, filename
              completion is attempted.
       possible-completions (M-?)
              List the possible completions of the text before point.
       insert-completions
              Insert all completions of the text before point that would have
              been generated by possible-completions.  By default, this is not
              bound to a key.
       complete-filename (M-/)
              Attempt filename completion on the text before point.
       possible-filename-completions (C-x /)
              List the possible completions of the text before point, treating
              it as a filename.
       complete-username (M-~)
              Attempt completion on the text before point, treating it as a
              username.
       possible-username-completions (C-x ~)
              List the possible completions of the text before point, treating
              it as a username.
       complete-variable (M-$)
              Attempt completion on the text before point, treating it as a
              shell variable.
       possible-variable-completions (C-x $)
              List the possible completions of the text before point, treating
              it as a shell variable.
       complete-hostname (M-@)
              Attempt completion on the text before point, treating it as a
              hostname.
       possible-hostname-completions (C-x @)
              List the possible completions of the text before point, treating
              it as a hostname.
       complete-command (M-!)
              Attempt completion on the text before point, treating it as a
              command name.  Command completion attempts to match the text
              against aliases, reserved words, shell functions, builtins, and
              finally executable filenames, in that order.
       possible-command-completions (C-x !)
              List the possible completions of the text before point, treating
              it as a command name.
       dynamic-complete-history (M-TAB)
              Attempt completion on the text before point, comparing the text
              against lines from the history list for possible completion
              matches.
       complete-into-braces (M-{)
              Perform filename completion and return the list of possible
              completions enclosed within braces so the list is available to the
              shell (see Brace Expansion above).

   Keyboard Macros
       start-kbd-macro (C-x ()
              Begin saving the characters typed into the current keyboard macro.
       end-kbd-macro (C-x ))
              Stop saving the characters typed into the current keyboard macro
              and save the definition.
       call-last-kbd-macro (C-x e)
              Re-execute the last keyboard macro defined, by making the
              characters in the macro appear as if typed at the keyboard.

   Miscellaneous
       re-read-init-file (C-x C-r)
              Read in the contents of your init file, and incorporate any
              bindings or variable assignments found there.
       abort (C-g)
              Abort the current editing command and ring the terminal's bell
              (subject to the setting of bell-style).
       do-uppercase-version (M-a, M-b, ...)
              Run the command that is bound to the corresponding uppercase
              character.
       prefix-meta (ESC)
              Metafy the next character typed.  ESC f is equivalent to Meta-f.
       undo (C-_, C-x C-u)
              Incremental undo, separately remembered for each line.
       revert-line (M-r)
              Undo all changes made to this line.  This is like typing the undo
              command enough times to return the line to its initial state.
       tilde-expand (M-~)
              Perform tilde expansion on the current word.
       dump-functions
              Print all of the functions and their key bindings to the readline
              output stream.  If a numeric argument is supplied, the output is
              formatted in such a way that it can be made part of an inputrc
              file.
       display-shell-version (C-x C-v)
              Display version information about the current instance of bash.

HISTORY
       When interactive, the shell provides access to the command history, the
       list of commands previously typed.  The text of the last HISTSIZE
       commands (default 500) is saved in a history list.  The shell stores each
       command in the history list prior to parameter and variable expansion
       (see EXPANSION above) but after history expansion is performed, subject
       to the values of the shell variables command_oriented_history and
       HISTCONTROL.  On startup, the history is initialized from the file named
       by the variable HISTFILE (default ~/.bash_history).  HISTFILE is
       truncated, if necessary, to contain no more than HISTFILESIZE lines.  The
       builtin command fc (see SHELL BUILTIN COMMANDS below) may be used to list
       or edit and re-execute a portion of the history list.  The history
       builtin can be used to display the history list and manipulate the
       history file.  When using the command-line editing, search commands are
       available in each editing mode that provide access to the history list.
       When an interactive shell exits, the last HISTSIZE lines are copied from
       the history list to HISTFILE.  If HISTFILE is unset, or if the history
       file is unwritable, the history is not saved.

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

       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 to determine 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 event, and the portions of that line that are acted upon
       are words.  The line is broken into words in the same fashion as when
       reading input, so that several metacharacter-separated words surrounded
       by quotes are considered as one word.  Only backslash (\) and single
       quotes can quote the history escape character, which is ! by default.

       The shell allows control of the various characters used by the history
       expansion mechanism (see the description of histchars above under Shell
       Variables).

   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 blank,
              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.
       !string
              Refer to the most recent command starting with string.
       !?string[?]
              Refer to the most recent command containing string.
       ^string1^string2^
              Quick substitution.  Repeat the last command, replacing string1
              with string2.  Equivalent to ``!!:s/string1/string2/'' (see
              Modifiers below).
       !#     The entire command line typed so far.

   Word Designators
       A : separates the event specification from the word designator.  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).

       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 `?string?' search.
       x-y    A range of words; `-y' abbreviates `0-y'.
       *      All of the words but the zeroth.  This is a synonym for `1-$'.  It
              is not an error to use * if there is just one word in the event;
              the empty string is returned in that case.
       x*     Abbreviates x-$.
       x-     Abbreviates x-$ like x*, but omits the last word.

   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 trailing suffix.
       t      Remove all leading pathname components, leaving the tail.
       p      Print the new command but do not execute it.
       q      Quote the substituted words, escaping further substitutions.
       x      Quote the substituted words as with q, but break into words at
              blanks and newlines.
       s/old/new/
              Substitute new for the first occurrence of old in the event line.
              Any delimiter can be used in place of /.  The final delimiter is
              optional if it is the last character of the event line.  The
              delimiter may be quoted in old and new with a single backslash.
              If & appears in new, it is replaced by old.  A single backslash
              will quote the &.
       &      Repeat the previous substitution.
       g      Cause changes to be applied over the entire event line.  This is
              used in conjunction with `:s' (e.g., `:gs/old/new/') or `:&'.  If
              used with `:s', any delimiter can be used in place of /, and the
              final delimiter is optional if it is the last character of the
              event line.

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
       levels are listed in order of decreasing precedence.

       - +    unary minus and plus
       ! ~    logical and bitwise negation
       * / %  multiplication, division, remainder
       + -    addition, subtraction
       << >>  left and right bitwise shifts
       <= >= < >
              comparison
       == !=  equality and inequality
       &      bitwise AND
       ^      bitwise exclusive OR
       |      bitwise OR
       &&     logical AND
       ||     logical OR
       = *= /= %= += -= <<= >>= &= ^= |=
              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.

       Constants with a leading 0 are interpreted as octal numbers.  A leading
       0x or 0X denotes hexadecimal.  Otherwise, numbers take the form [base#]n,
       where base is a decimal number between 2 and 36 representing the
       arithmetic base, and n is a number in that base.  If base is omitted,
       then base 10 is used.

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

SHELL BUILTIN COMMANDS
       : [arguments]
              No effect; the command does nothing beyond expanding arguments and
              performing any specified redirections.  A zero exit code is
              returned.

        .  filename [arguments]
       source filename [arguments]
              Read and execute commands from filename in the current shell
              environment and return the exit status of the last command
              executed from filename.  If filename does not contain a slash,
              pathnames in PATH are used to find the directory containing
              filename.  The file searched for in PATH need not be executable.
              The current directory is searched if no file is found in PATH.  If
              any arguments are supplied, they become the positional parameters
              when file is executed.  Otherwise the positional parameters are
              unchanged.  The return status is the status of the last command
              exited within the script (0 if no commands are executed), and
              false if filename is not found.

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

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

       bind [-m keymap] [-lvd] [-q name]
       bind [-m keymap] -f filename
       bind [-m keymap] keyseq:function-name
              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 .inputrc, 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:
              -m keymap
                     Use keymap as the keymap to be affected by the subsequent
                     bindings.  Acceptable keymap names are emacs, emacs-
                     standard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command,
                     and vi-insert.  vi is equivalent to vi-command; emacs is
                     equivalent to emacs-standard.
              -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 filename
                     Read key bindings from filename
              -q function
                     Query about which keys invoke the named function

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

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

       builtin shell-builtin [arguments]
              Execute the specified shell builtin, passing it arguments, 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.  The return status is
              false if shell-builtin is not a shell builtin command.

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

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

       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
              continue is executed.

       declare [-frxi] [name[=value]]
       typeset [-frxi] [name[=value]]
              Declare variables and/or give them attributes.  If no names are
              given, then display the values of variables instead.  The options
              can be used to restrict output to variables with the specified
              attribute.
              -f     Use function names only
              -r     Make names readonly.  These names cannot then be assigned
                     values by subsequent assignment statements.
              -x     Mark names for export to subsequent commands via the
                     environment.
              -i     The variable is treated as an integer; arithmetic
                     evaluation (see ARITHMETIC EVALUATION ) is performed when
                     the variable is assigned a value.

              Using `+' instead of `-' turns off the attribute instead.  When
              used in a function, makes names local, as with the local command.
              The return value is 0 unless an illegal option is encountered, an
              attempt is made to define a function using "-f foo=bar", one of
              the names is not a legal shell variable name, an attempt is made
              to turn off readonly status for a readonly variable, or an attempt
              is made to display a non-existant function with -f.

       dirs [-l] [+/-n]
              Display the list of currently remembered directories.  Directories
              are added to the list with the pushd command; the popd command
              moves back up through the list.
              +n     displays the nth entry counting from the left of the list
                     shown by dirs when invoked without options, starting with
                     zero.
              -n     displays the nth entry counting from the right of the list
                     shown by dirs when invoked without options, starting with
                     zero.
              -l     produces a longer listing; the default listing format uses
                     a tilde to denote the home directory.

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

       echo [-neE] [arg ...]
              Output the args, separated by spaces.  The return status is always
              0.  If -n is specified, the trailing newline is suppressed.  If
              the -e option is given, interpretation of the following backslash-
              escaped characters is enabled.  The -E option disables the
              interpretation of these escape characters, even on systems where
              they are interpreted by default.
              \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 nnn (octal)

       enable [-n] [-all] [name ...]
              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
              name is disabled; otherwise, names are enabled.  For example, to
              use the test binary found via the PATH instead of the shell
              builtin version, type ``enable -n test''.  If no arguments are
              given, a list of all enabled shell builtins is printed.  If only
              -n is supplied, a list of all disabled builtins is printed.  If
              only -all is supplied, the list printed includes all builtins,
              with an indication of whether or not each is enabled.  enable
              accepts -a as a synonym for -all.  The return value is 0 unless a
              name is not a shell builtin.

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

       exec [[-] command [arguments]]
              If command is specified, it replaces the shell.  No new process is
              created.  The arguments become the arguments to command.  If the
              first argument is -, the shell places a dash in the zeroth arg
              passed to command.  This is what login does.  If the file cannot
              be executed for some reason, a non-interactive shell exits, unless
              the shell variable no_exit_on_failed_exec exists, in which case it
              returns failure.  An interactive shell returns failure if the file
              cannot be executed.  If command is not specified, any redirections
              take effect in the current shell, and the return status is 0.

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

       export [-nf] [name[=word]] ...
       export -p
              The supplied names are marked for automatic export to the
              environment of subsequently executed commands.  If the -f option
              is given, the names refer to functions.  If no names are given, or
              if the -p option is supplied, a list of 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 0 unless an illegal
              option is encountered, one of the names is not a legal shell
              variable name, or -f is supplied with a name that is not a
              function.

       fc [-e ename] [-nlr] [first] [last]
       fc -s [pat=rep] [cmd]
              Fix Command.  In the first form, a range of commands from first to
              last is selected from the history list.  First and last may be
              specified as a string (to locate the last command beginning with
              that string) or as a number (an index into the history list, where
              a negative number is used as an offset from the current command
              number).  If last is not specified it is set to the current
              command for listing (so that fc -l -10 prints the last 10
              commands) and to first otherwise.  If first is not specified it is
              set to the previous command for editing and -16 for listing.

              The -n flag suppresses the command numbers when listing.  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 ename is invoked on a file containing those commands.  If
              ename is not given, the value of the FCEDIT variable is used, and
              the value of EDITOR if FCEDIT is not set.  If neither variable is
              set, vi is used.  When editing is complete, the edited commands
              are echoed and executed.

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

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

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

       getopts optstring name [args]
              getopts is used by shell procedures to parse positional
              parameters.  optstring contains the option 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 name, initializing name if it does
              not exist, and the index of the next argument to be processed into
              the variable OPTIND.  OPTIND is initialized to 1 each time the
              shell or a shell script is invoked.  When an option requires an
              argument, getopts places that argument into the variable OPTARG.
              The shell does not reset OPTIND automatically; it must be manually
              reset between multiple calls to getopts within the same shell
              invocation if a new set of parameters is to be used.

              getopts can report errors in two ways.  If the first character of
              optstring is a colon, silent error reporting is used.  In normal
              operation diagnostic messages are printed when 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 optstring is not a colon.

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

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

              getopts normally parses the positional parameters, but if more
              arguments are given in args, 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] [name]
              For each name, the full pathname of the command is determined and
              remembered.  The -r option causes the shell to forget all
              remembered locations.  If no arguments 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 name is not found or an illegal option is
              supplied.

       help [pattern]
              Display helpful information about builtin commands.  If pattern is
              specified, help gives detailed help on all commands matching
              pattern; otherwise a list of the builtins is printed.  The return
              status is 0 unless no command matches pattern.

       history [n]
       history -rwan [filename]
              With no options, display the command history list with line
              numbers.  Lines listed with a * have been modified.  An argument
              of n lists only the last n lines.  If a non-option argument is
              supplied, it is used as the name of the history file; if not, the
              value of HISTFILE is used.  Options, if supplied, have the
              following meanings:
              -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.

              The return value is 0 unless an illegal option is encountered or
              an error occurs while reading or writing the history file.

       jobs [-lnp] [ jobspec ... ]
       jobs -x command [ args ... ]
              The first form 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
              notified.  If jobspec is given, output is restricted to
              information about that job.  The return status is 0 unless an
              illegal option is encountered or an illegal jobspec is supplied.

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

       kill [-s sigspec | -sigspec] [pid | jobspec] ...
       kill -l [signum]
              Send the signal named by sigspec to the processes named by pid or
              jobspec.  sigspec is either a signal name such as SIGKILL or a
              signal number.  If sigspec is a signal name, the name is case
              insensitive and may be given with or without the SIG prefix.  If
              sigspec is not present, then SIGTERM is assumed.  An argument of
              -l lists the signal names.  If any arguments are supplied when -l
              is given, the names of the specified signals are listed, and the
              return status is 0.  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 or an
              illegal option is encountered.

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

       local [name[=value] ...]
              For each argument, create a local variable named name, and assign
              it value.  When local is used within a function, it causes the
              variable name 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.  The return status is 0 unless local
              is used outside a function, or an illegal name is supplied.

       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 popd command is successful, a dirs is performed as well,
              and the return status is 0.  popd returns false if an illegal
              option is encountered, the directory stack is empty, a non-
              existent directory stack entry is specified, or the directory
              change fails.

       pushd [dir]
       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
              and returns 0, unless the directory stack is empty.
              +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 dir to the directory stack at the top, making it the
                     new current working directory.

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

       pwd    Print the absolute pathname of the current working directory.  The
              path printed contains no symbolic links if the -P option to the
              set builtin command is set.  See also the description of nolinks
              under Shell Variables above).  The return status is 0 unless an
              error occurs while reading the pathname of the current directory.

       read [-r] [name ...]
              One line is read from the standard input, and the first word is
              assigned to the first name, the second word to the second name,
              and so on, with leftover words assigned to the last name.  Only
              the characters in IFS are recognized as word delimiters.  If no
              names are supplied, the line read is assigned to the variable
              REPLY.  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 [-f] [name ...]
       readonly -p
              The given names are marked readonly and the values of these names
              may not be changed by subsequent assignment.  If the -f option is
              supplied, the functions corresponding to the names are so marked.
              If no arguments 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 arguments.  The return status
              is 0 unless an illegal option is encountered, one of the names is
              not a legal shell variable name, or -f is supplied with a name
              that is not a function.

       return [n]
              Causes a function to exit with the return value specified 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.  If used outside a function and not
              during execution of a script by ., the return status is false.

       set [--abefhkmnptuvxldCHP] [-o option] [arg ...]
              -a      Automatically mark variables which are modified or created
                      for export to the environment of subsequent commands.
              -b      Cause the status of terminated background jobs to be
                      reported immediately, rather than before the next primary
                      prompt.  (Also see notify under Shell Variables above).
              -e      Exit immediately if a simple-command (see SHELL GRAMMAR
                      above) exits with a non-zero status.  The shell does not
                      exit if the command that fails is part of an until or
                      while loop, part of an if statement, part of a && or ⎪⎪
                      list, or if the command's return value is being inverted
                      via !.
              -f      Disable pathname expansion.
              -h      Locate and remember function commands as functions are
                      defined.  Function commands are normally 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 option-name
                      The option-name can be one of the following:
                      allexport
                              Same as -a.
                      braceexpand
                              The shell performs brace expansion (see Brace
                              Expansion above).  This is on by default.
                      emacs   Use an emacs-style command line editing interface.
                              This is enabled by default when the shell is
                              interactive, unless the shell is started with the
                              -nolineediting option.
                      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).
                      interactive-comments
                              Allow a word beginning with # to cause that word
                              and all remaining characters on that line to be
                              ignored in an interactive shell (see COMMENTS
                              above).
                      monitor Same as -m.
                      noclobber
                              Same as -C.
                      noexec  Same as -n.
                      noglob  Same as -f.
                      nohash  Same as -d.
                      notify  Same as -b.
                      nounset Same as -u.
                      physical
                              Same as -P.
                      posix   Change the behavior of bash where the default
                              operation differs from the Posix 1003.2 standard
                              to match the standard.
                      privileged
                              Same as -p.
                      verbose Same as -v.
                      vi      Use a vi-style command line editing interface.
                      xtrace  Same as -x.
                      If no option-name is supplied, the values of the current
                      options are printed.
              -p      Turn on privileged mode.  In this mode, the $ENV file is
                      not processed, and shell functions are not inherited from
                      the environment.  This is enabled automatically on startup
                      if the effective user (group) id is not equal to the real
                      user (group) id.  Turning this option off causes the
                      effective user and group ids to be set to the real user
                      and group ids.
              -t      Exit after reading and executing one command.
              -u      Treat unset variables as an error when performing
                      parameter expansion.  If expansion is attempted on an
                      unset variable, the shell prints an error message, and, if
                      not interactive, exits with a non-zero status.
              -v      Print shell input lines as they are read.
              -x      After expanding each simple-command, bash displays the
                      expanded value of PS4, followed by the command and its
                      expanded arguments.
              -l      Save and restore the binding of name in a for name [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 Variables above).
              -H      Enable !  style history substitution.  This flag is on by
                      default when the shell is interactive.
              -P      If set, do not follow symbolic links when performing
                      commands such as cd which change the current directory.
                      The physical directory is used instead.
              --      If no arguments follow this flag, then the positional
                      parameters are unset.  Otherwise, the positional
                      parameters are set to the args, even if some of them begin
                      with a -.
              -       Signal the end of options, cause all remaining args to be
                      assigned to the positional parameters.  The -x and -v
                      options are turned off.  If there are no args, the
                      positional parameters remain unchanged.

              The flags are off by default unless otherwise noted.  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 processed, the remaining n args are treated as
              values for the positional parameters and are assigned, in order,
              to $1, $2, ...  $n.  If no options or args 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 ....
              Parameters represented by the numbers $# down to $#-n+1 are unset.
              If n is 0, no parameters are changed.  If n is not given, it is
              assumed to be 1.  n must be a non-negative number less than or
              equal to $#.  If n is greater than $#, the positional parameters
              are not changed.  The return status is greater than 0 if n is
              greater than $# or less than 0; 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.  The return status is 0 unless the
              shell is a login shell and -f is not supplied, or if job control
              is not enabled.

       test expr
       [ expr ]
              Return a status of 0 (true) or 1 (false) depending on the
              evaluation of the conditional expression expr.  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.  Each operator and operand must be a
              separate argument.  If file is of the form /dev/fd/n, then file
              descriptor n is checked.
              -b file
                     True if file exists and is block special.
              -c file
                     True if file exists and is character special.
              -d file
                     True if file exists and is a directory.
              -e file
                     True if file exists.
              -f file
                     True if file exists and is a regular file.
              -g file
                     True if file exists and is set-group-id.
              -k file
                     True if file has its ``sticky'' bit set.
              -L file
                     True if file exists and is a symbolic link.
              -p file
                     True if file exists and is a named pipe.
              -r file
                     True if file exists and is readable.
              -s file
                     True if file exists and has a size greater than zero.
              -S file
                     True if file exists and is a socket.
              -t fd  True if fd is opened on a terminal.
              -u file
                     True if file exists and its set-user-id bit is set.
              -w file
                     True if file exists and is writable.
              -x file
                     True if file exists and is executable.
              -O file
                     True if file exists and is owned by the effective user id.
              -G file
                     True if file exists and is owned by the effective group id.
              file1 -nt file2
                     True if file1 is newer (according to modification date)
                     than file2.
              file1 -ot file2
                     True if file1 is older than file2.
              file1 -ef file
                     True if file1 and file2 have the same device and inode
                     numbers.
              -z string
                     True if the length of string is zero.
              -n string
              string True if the length of string is non-zero.
              string1 = string2
                     True if the strings are equal.
              string1 != string2
                     True if the strings are not equal.
              ! expr True if expr is false.
              expr1 -a expr2
                     True if both expr1 AND expr2 are true.
              expr1 -o expr2
                     True if either expr1 OR expr2 is true.
              arg1 OP arg2
                     OP is one of -eq, -ne, -lt, -le, -gt, or -ge.  These
                     arithmetic binary operators return true if arg1 is equal,
                     not-equal, less-than, less-than-or-equal, greater-than, or
                     greater-than-or-equal than arg2, respectively.  Arg1 and
                     arg2 may be positive integers, negative integers, or the
                     special expression -l string, which evaluates to the length
                     of string.

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

       trap [-l] [arg] [sigspec]
              The command arg is to be read and executed when the shell receives
              signal(s) sigspec.  If arg is absent or -, all specified signals
              are reset to their original values (the values they had upon
              entrance to the shell).  If arg is the null string this signal is
              ignored by the shell and by the commands it invokes.  sigspec is
              either a signal name defined in <signal.h>, or a signal number.
              If sigspec is EXIT (0) the command arg 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 the trap name or number is invalid; otherwise
              trap returns true.

       type [-all] [-type | -path] name [name ...]
              With no options, indicate how each name would be interpreted if
              used as a command name.  If the -type flag is used, type prints a
              phrase which is one of alias, keyword, function, builtin, or file
              if name is an alias, shell reserved word, function, builtin, or
              disk file, respectively. If the name is not found, then nothing is
              printed, and an exit status of false is returned.  If the -path
              flag is used, type either returns the name of the disk file that
              would be executed if name were specified as a command name, or
              nothing if -type would not return file.  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 name.  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 [-SHacdfmstpnuv [limit]]
              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 limit 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 limit
              is omitted, the current value of the soft limit of the resource is
              printed, unless the H option is given.  When more than one
              resource is specified, the limit name and unit is printed before
              the value.  Other options are interpreted 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)
              -u     the maximum number of processes available to a single user
              -v     The maximum amount of virtual memory available to the shell

              An argument of -- disables option checking for the rest of the
              arguments.  If limit 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, -p, which is in units of
              512-byte blocks, and -n and -u, which are unscaled values.  The
              return status is 0 unless an illegal option is encountered, a non-
              numeric argument other than unlimited is supplied as limit, or an
              error occurs while setting a new limit.

       umask [-S] [mode]
              The user file-creation mask is set to mode.  If mode begins with a
              digit, it is interpreted as an octal number; otherwise it is
              interpreted as a symbolic mode mask similar to that accepted by
              chmod(1).  If mode is omitted, 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.  The return status is 0 if the mode was
              successfully changed or if no mode argument was supplied, and
              false otherwise.

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

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

       wait [n]
              Wait for the specified process and return its termination status.
              n may be a process ID or a job specification; if a job spec is
              given, all processes in that job's pipeline are waited for.  If n
              is not given, all currently active child processes are waited for,
              and the return status is zero.  If n specifies a non-existant
              process or job, the return status is 127.  Otherwise, the return
              status is the exit status of the last process or job waited for.

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

       An interactive shell is one whose standard input and output are both
       connected to terminals (as determined by isatty(3)), or one started with
       the -i option.  PS1 is set and $- includes i if bash is interactive,
       allowing a shell script or a startup file to test this state.

       Login shells:
         On login (subject to the -noprofile option):
               if /etc/profile exists, source it.

               if ~/.bash_profile exists, source it,
                 else if ~/.bash_login exists, source it,
                   else if ~/.profile exists, source it.

         On exit:
               if ~/.bash_logout exists, source it.

       Non-login interactive shells:
         On startup (subject to the -norc and -rcfile options):
               if ~/.bashrc exists, source it.

       Non-interactive shells:
         On startup:
               if the environment variable ENV is non-null, expand
               it and source the file it names, as if the command
                       if [ "$ENV" ]; then . $ENV; fi
               had been executed, but do not use PATH to search
               for the pathname.  When not started in Posix mode, bash
               looks for BASH_ENV before ENV.

       If Bash is invoked as sh, it tries to mimic the behavior of sh as closely
       as possible.  For a login shell, it attempts to source only /etc/profile
       and ~/.profile, in that order.  The -noprofile option may still be used
       to disable this behavior.  A shell invoked as sh does not attempt to
       source any other startup files.

       When bash is started in posix mode, as with the -posix command line
       option, it follows the Posix standard for startup files.  In this mode,
       the ENV variable is expanded and that file sourced; no other startup
       files are read.

SEE ALSO
       Bash Features, Brian Fox and Chet Ramey
       The Gnu Readline Library, Brian Fox and Chet Ramey
       The Gnu History Library, Brian Fox and Chet Ramey
       A System V Compatible Implementation of 4.2BSD Job Control, David Lennert
       Portable Operating System Interface (POSIX) Part 2: Shell and Utilities,
       IEEE
       sh(1), ksh(1), csh(1)
       emacs(1), vi(1)
       readline(3)

FILES
       /bin/bash
              The bash executable
       /etc/profile
              The systemwide initialization file, executed for login shells
       ~/.bash_profile
              The personal initialization file, executed for login shells
       ~/.bashrc
              The individual per-interactive-shell startup file
       ~/.inputrc
              Individual readline initialization file

AUTHORS
              Brian Fox, Free Software Foundation (primary author)
              bfox@ai.MIT.Edu

              Chet Ramey, Case Western Reserve University
              chet@ins.CWRU.Edu

BUG REPORTS
       If you find a bug in bash, you should report it.  But first, you should
       make sure that it really is a bug, and that it appears in the latest
       version of bash that you have.

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

       ALL bug reports should include:

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

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

       Comments and bug reports concerning this manual page should be directed
       to chet@ins.CWRU.Edu.

BUGS
       It's too big and too slow.

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

       Aliases are confusing in some uses.




GNU                                1995 May 5                            BASH(1)