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BASH内置手册

BASH_BUILTINS(1)                 General Commands Manual          BASH_BUILTINS(1)  

1、名称

名称 名称 名称
bash eval read
: exec readonly
. exit return
[ export set
alias false shift
bg fc shopt
bind fg source
break getopts suspend
builtin hash test
caller help times
cd history trap
command jobs true
compgen kill type
complete let typeset
compopt local ulimit
continue logout umask
declare mapfile unalias
dirs popd unset
disown printf wait
echo pushd
enable pwd

2、bash内置命令

说明:

    Unless otherwise noted, each builtin command documented in this section as accepting options preceded by - accepts -- to signify the end of the options.  The :, true, false, and test builtins do not accept options and do not treat -- specially.  The exit, logout, break, continue, let, and shift builtins accept and process arguments beginning with -  without  requiring  --.   Other builtins that accept arguments but are not specified as accepting options interpret arguments beginning with - as invalid options and require -- to prevent this interpretation.
: [arguments]
        No effect; the command does nothing beyond expanding arguments and performing any 
        specified redirections.  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, file names in PATH are used to find the directory containing 
        filename.  The file searched for in PATH need not be executable.  When bash is not 
        in posix mode, the current directory  is searched  if  no  file is found in PATH.  
        If the sourcepath option to the shopt builtin command is turned off, the PATH is not 
        searched.  If any arguments are supplied, they become the positional parameters when 
        filename is executed.  Otherwise the positional parameters are unchanged.  The 
        return status is the status of the last command exited within the script (0 if no 
        commands are executed), and false if filename is not found or cannot be read.
alias [-p] [name[=value] ...]
        Alias  with  no  arguments  or with the -p option prints the list of aliases in the 
        form alias name=value on standard output.  When arguments are supplied, an alias is 
        defined for each name whose value is given.  A trailing space in  value causes the 
        next word to be checked for alias substitution when the alias is expanded.  For each 
        name in  the  argument  list  for which no value is supplied, the name and value of 
        the alias is printed.  Alias returns true unless a name is given for which no alias 
        has been defined.
bg [jobspec ...]
        Resume  each suspended job jobspec in the background, as if it had been started with 
        &.  If jobspec is not present, the shell's notion of the current job is used.  bg 
        jobspec returns 0 unless run when job control is disabled or, when run with job 
        control enabled, any specified jobspec was not found or was started without job 
        control.
bind [-m keymap] [-lpsvPSV]
bind [-m keymap] [-q function] [-u function] [-r keyseq]
bind [-m keymap] -f filename
bind [-m keymap] -x keyseq:shell-command
bind [-m keymap] keyseq:function-name
bind readline-command
        Display current readline key and function bindings, bind a key sequence to a 
        readline function or macro, or set a readline variable.  Each non-option argument is 
        a command as it  would appear in .inputrc, but each binding or command must be 
        passed as a separate argument; e.g., '"\C-x\C-r": re-read-init-file'.  Options, if 
        supplied, have the following meanings:
        -m keymap
        Use  keymap  as  the  keymap  to be affected by the subsequent bindings.
        Acceptable keymap names are emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-
        move, vi-command, and vi-insert.  vi is equivalent to vi-command; emacs is 
        equivalent to emacs-standard.
    -l     
        List the names of all readline functions.
    -p     
        Display readline function names and bindings in such a way that they can be re-read.
    -P     
        List current readline function names and bindings.
    -s     
        Display readline key sequences bound to macros and the strings they output in such a 
        way that they can be re-read.
    -S     
        Display readline key sequences bound to macros and the strings they output.
    -v     
        Display readline variable names and values in such a way that they can be re-read.
    -V     
        List current readline variable names and values.
    -f filename
        Read key bindings from filename.
    -q function
        Query about which keys invoke the named function.
    -u function
        Unbind all keys bound to the named function.
    -r keyseq
        Remove any current binding for keyseq.
    -x keyseq:shell-command
        Cause shell-command to be executed whenever keyseq is entered.  When shell-command 
        is executed, the shell sets the READLINE_LINE variable to the contents of  the  
        readline  line buffer  and  the READLINE_POINT variable to the current location of 
        the insertion point.  If the executed command changes the value of READLINE_LINE or 
        READLINE_POINT, those newvalues will be reflected in the editing state.

    The return value is 0 unless an unrecognized option is given or an error occurred.
break [n]
        Exit from within a for, while, until, or select loop.  If n is specified, break n 
        levels.  n must be ≥ 1.  If n is greater than the number of enclosing loops, all 
        enclosing  loops  are exited.  The return value is non-zero when n is ≤ 0; 
        Otherwise, break returns 0 value.
builtin shell-builtin [arguments]
        Execute the specified shell builtin, passing it arguments, and return its exit 
        status.  This is useful when defining a function whose name is the same as a shell 
        builtin, retaining the functionality of the builtin within the function.  The cd 
        builtin is commonly redefined this way.  The return status is false if shell-builtin 
        is not a shell builtin command.
caller [expr]
        Returns the context of any active subroutine call (a shell function or a script 
        executed with the . or source builtins).  Without expr, caller displays the line 
        number and source file‐name of the current subroutine call.  If a non-negative 
        integer is supplied as expr, caller displays the line number, subroutine name, and 
        source file corresponding to that position in the current execution call stack.  
        This extra information may be used, for example, to print a stack trace.  The 
        current frame is frame 0.  The return value is 0 unless  the  shell  is not 
        executing a subroutine call or expr does not correspond to a valid position in the 
        call stack.
cd [-L|[-P [-e]]] [dir]
        Change the current directory to dir.  The variable HOME is the default dir.  The 
        variable CDPATH defines the search path for the directory containing dir.  
        Alternative directory names in CDPATH are separated by a colon (:).  A null 
        directory name in CDPATH is the same as the current directory, i.e., ``.''.  If dir 
        begins with a slash (/), then CDPATH  is  not  used.
        The  -P option says to use the physical directory structure instead of following 
        symbolic links (see also the -P option to the set builtin command); the -L option 
        forces symbolic links to be followed.  If the -e option is supplied with -P, and the 
        current working directory cannot be successfully determined after a successful 
        directory change, cd will return an unsuc‐cessful  status.   An argument of - is 
        equivalent to $OLDPWD.  If a non-empty directory name from CDPATH is used, or if - 
        is the first argument, and the directory change is successful, the absolute pathname 
        of the new working directory is written to the standard output.  The return value is 
        true if the directory was successfully changed; false otherwise.
command [-pVv] command [arg ...]
        Run command with args suppressing the normal shell function lookup. Only builtin 
        commands or commands found in the PATH are executed.  If the -p option is given, the 
        search for command is  performed  using a default value for PATH that is guaranteed 
        to find all of the standard utilities.  If either the -V or -v option is supplied, a 
        description of command is printed. 
        The -v option causes a single word indicating the command or file name used to 
        invoke command to be displayed; the -V option produces a more verbose  description.   
        If  the  -V  or  -v option  is  supplied,  the exit status is 0 if command was 
        found, and 1 if not.  If neither option is supplied and an error occurred or command 
        cannot be found, the exit status is 127. Otherwise, the exit status of the command 
        builtin is the exit status of command.
compgen [option] [word]
        Generate possible completion matches for word according to the options, which may be 
        any option accepted by the complete builtin with the exception of -p and -r, and 
        write the  matches to the standard output.  When using the -F or -C options, the 
        various shell variables set by the programmable completion facilities, while 
        available, will not have useful values.

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

        The return value is true unless an invalid option is supplied, or no matches were 
        generated.
complete [-abcdefgjksuv] [-o comp-option] [-DE] [-A action] [-G globpat] [-W wordlist] 
         [-F function] [-C command] [-X filterpat] [-P prefix] [-S suffix] name [name ...]
complete -pr [-DE] [name ...]
        Specify how arguments to each name should be completed.  If the -p option is 
        supplied, or if no options are supplied, existing completion specifications  are  
        printed  in  a  way  that allows  them  to  be reused as input.  The -r option 
        removes a completion specification for each name, or, if no names are supplied, all 
        completion specifications.  The -D option indicates that the remaining options and 
        actions should apply to the ``default'' command completion; that is, completion 
        attempted on a command for which no completion has previously  been defined.  The -
        E option indicates that the remaining options and actions should apply to ``empty'' 
        command completion; that is, completion attempted on a blank line.

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

        Other  options, if specified, have the following meanings.  The arguments to the -
        G, -W, and -X options (and, if necessary, the -P and -S options) should be quoted 
        to protect them from expansion before the complete builtin is invoked.
    -o comp-option
        The comp-option controls several aspects of the compspec's behavior beyond the 
        simple generation of completions.  comp-option may be one of:

        bashdefault
            Perform the rest of the default bash completions if the compspec generates no 
            matches.
        default 
            Use readline's default filename completion if the compspec generates no matches.
        dirnames
            Perform directory name completion if the compspec generates no matches.
        filenames
            Tell readline that the compspec generates filenames, so it can perform any 
            filename-specific processing (like adding a slash to directory names, quoting 
            special characters, or suppressing trailing spaces).  Intended to be used with 
            shell functions.
        nospace 
            Tell readline not to append a space (the default) to words completed at the end 
            of the line.
        plusdirs
            After any matches defined by the compspec are generated, directory name 
            completion is attempted and any matches are added to the results of the other 
            actions.
    -A action
        The action may be one of the following to generate a list of possible completions:

        alias   Alias names.  May also be specified as -a.
        arrayvar
                Array variable names.
        binding 
                Readline key binding names.
        builtin 
                Names of shell builtin commands.  May also be specified as -b.
        command 
                Command names.  May also be specified as -c.
        directory
                Directory names.  May also be specified as -d.
        disabled
                Names of disabled shell builtins.
        enabled 
                Names of enabled shell builtins.
        export  
                Names of exported shell variables.  May also be specified as -e.
        file    File names.  May also be specified as -f.
        function 
                Names of shell functions.
        group   Group names.  May also be specified as -g.
        helptopic
                Help topics as accepted by the help builtin.
        hostname
                Hostnames, as taken from the file specified by the HOSTFILE shell variable.
        job     Job names, if job control is active.  May also be specified as -j.
        keyword Shell reserved words.  May also be specified as -k.
        running Names of running jobs, if job control is active.
        service Service names.  May also be specified as -s.
        setopt  Valid arguments for the -o option to the set builtin.
        shopt   Shell option names as accepted by the shopt builtin.
        signal  Signal names.
        stopped Names of stopped jobs, if job control is active.
        user    User names.  May also be specified as -u.
        variable
                Names of all shell variables.  May also be specified as -v.
    -C command
        command is executed in a subshell environment, and its output is used as the 
        possible completions.
    -F function
        The  shell function function is executed in the current shell environment.  When it 
        finishes, the possible completions are retrieved from the value of the COMPREPLY 
        array variable.
    -G globpat
        The pathname expansion pattern globpat is expanded to generate the possible 
        completions.
    -P prefix
        prefix is added at the beginning of each possible completion after all other options 
        have been applied.
    -S suffix
        suffix is appended to each possible completion after all other options have been 
        applied.
    -W wordlist
        The wordlist is split using the characters in the IFS special variable as 
        delimiters, and each resultant word is expanded.  The possible completions  are  the  
        members  of  the resultant list which match the word being completed.
    -X filterpat
        filterpat  is a pattern as used for pathname expansion.  It is applied to the list 
        of possible completions generated by the preceding options and arguments, and each 
        completion matching filterpat is removed from the list.  A leading ! in filterpat 
        negates the pattern; in this case, any completion not matching filterpat is removed.

    The return value is true unless an invalid option is supplied, an option other than -p 
    or -r is supplied without a name argument, an attempt is made to remove a  completion  
    specification for a name for which no specification exists, or an error occurs adding a 
    completion specification.
compopt [-o option] [-DE] [+o option] [name]
              Modify  completion  options for each name according to the options, or for the 
              currently-executing completion if no names are supplied.  If no options are 
              given, display the completion options for each name or the current completion.  
              The possible values of option are those valid for the complete builtin 
              described above.  The -D option indicates  that  the  remaining
              options  should  apply  to  the ``default'' command completion; that is, 
              completion attempted on a command for which no completion has previously been 
              defined.  The -E option indicates that the remaining options should apply to 
              ``empty'' command completion; that is, completion attempted on a blank line.

              The return value is true unless an invalid option is supplied, an attempt is
              made to modify the options for a name for which no completion specification  
              exists,  or  an  output  error occurs.
continue [n]
              Resume  the next iteration of the enclosing for, while, until, or select loop.  
              If n is specified, resume at the nth enclosing loop.  n must be ≥ 1.  If n is 
              greater than the number of enclosing loops, the last enclosing loop (the 
              ``top-level'' loop) is resumed.  When continue is executed inside of loop, the 
              return value is non-zero when n is ≤ 0; Otherwise, continue
              returns 0 value. When continue is executed outside of loop, the return value 
              is 0.
 declare [-aAfFgilrtux] [-p] [name[=value] ...]
typeset [-aAfFgilrtux] [-p] [name[=value] ...]
              Declare variables and/or give them attributes.  If no names are given then 
              display the values of variables.  The -p option will display the attributes 
              and values of each name.  When -p is used with name arguments, additional 
              options are ignored.  When -p is supplied without name arguments, it will 
              display  the  attributes  and  values  of  all  variables  having  the
              attributes  specified  by  the additional options.  If no other options are 
              supplied with -p, declare will display the attributes and values of all shell 
              variables.  The -f option will restrict the display to shell functions.  The -
              F option inhibits the display of function definitions; only the function name 
              and attributes are printed.  If the extdebug  shell  option is  enabled using 
              shopt, the source file name and line number where the function is defined are 
              displayed as well.  The -F option implies -f.  The -g option forces variables 
              to be created or modified at the global scope, even when declare is executed 
              in a shell function.  It is ignored in all other cases.  The following options 
              can be used  to  restrict  output  to variables with the specified attribute 
              or to give variables attributes:
              -a     Each name is an indexed array variable (see Arrays above).
              -A     Each name is an associative array variable (see Arrays above).
              -f     Use function names only.
              -i     The variable is treated as an integer; arithmetic evaluation (see 
                     ARITHMETIC EVALUATION above) is performed when the variable is assigned 
                     a value.
              -l     When the variable is assigned a value, all upper-case characters are 
                     converted to lower-case.  The upper-case attribute is disabled.
              -r     Make names readonly.  These names cannot then be assigned values by 
                     subsequent assignment statements or unset.
              -t     Give each name the trace attribute.  Traced functions inherit the DEBUG 
                     and RETURN traps from the calling shell.  The trace attribute has no 
                     special meaning for variables.
              -u     When the variable is assigned a value, all lower-case characters are 
                     converted to upper-case.  The lower-case attribute is disabled.
              -x     Mark names for export to subsequent commands via the environment.

              Using  `+' instead of `-' turns off the attribute instead, with the exceptions 
              that +a may not be used to destroy an array variable and +r will not remove 
              the readonly attribute.  When
              used in a function, makes each name local, as with the local command, unless 
              the -g option is supplied, If a variable name is followed by =value, the value 
              of the variable  is  set  to value.   The return value is 0 unless an invalid 
              option is encountered, an attempt is made to define a function using ``-f 
              foo=bar'', an attempt is made to assign a value to a readonly variable, an 
              attempt is made to assign a value to an array variable without using the 
              compound assignment syntax (see Arrays above), one of the names is  not  a  
              valid  shell  variable name, an attempt is made to turn off readonly status 
              for a readonly variable, an attempt is made to turn off array status for an 
              array variable, or an attempt is made to display a non-existent function with 
              -f.
dirs [+n] [-n] [-clpv]
              Without options, displays the list of currently remembered directories.  The 
              default display is on a single line with directory names separated by spaces.  
              Directories are added to the
              list with the pushd command; the popd command removes entries from the list.

              +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.
              -c     Clears the directory stack by deleting all of the entries.
              -l     Produces a longer listing; the default listing format uses a tilde to 
                     denote the home directory.
              -p     Print the directory stack with one entry per line.
              -v     Print the directory stack with one entry per line, prefixing each entry 
                     with its index in the stack.

              The return value is 0 unless an invalid option is supplied or n indexes beyond 
              the end of the directory stack.
disown [-ar] [-h] [jobspec ...]
              Without  options,  each  jobspec is removed from the table of active jobs.  If 
              jobspec is not present, and neither -a nor -r is supplied, the shell's notion 
              of the current job is used.
              If the -h option is given, each jobspec is not removed from the table, but is 
              marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP.  
              If no  jobspec  is  present, and  neither  the -a nor the -r option is 
              supplied, the current job is used.  If no jobspec is supplied, the -a option 
              means to remove or mark all jobs; the -r option without a jobspec argument 
              restricts operation to running jobs.  The return value is 0 unless a jobspec 
              does not specify a valid job.
echo [-neE] [arg ...]
              Output the args, separated by spaces, followed by a newline.  The return 
              status is always 0.  If -n is specified, the trailing newline is suppressed.  
              If the -e option is given, inter-pretation of the following backslash-escaped 
              characters is enabled.  The -E option disables the interpretation of these 
              escape characters, even on systems where they are interpreted by default.  The 
              xpg_echo shell option may be used to dynamically determine whether or not echo 
              expands these escape characters by default.  echo does not interpret -- to 
              mean the end  of options.  echo interprets the following escape sequences:

              \a     alert (bell)
              \b     backspace
              \c     suppress further output
              \e
              \E     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \0nnn  the eight-bit character whose value is the octal value nnn (zero to 
                     three octal digits)
              \xHH   the eight-bit character whose value is the hexadecimal value HH (one or 
                     two hex digits)
              \uHHHH the Unicode (ISO/IEC 10646) character whose value is the hexadecimal 
                     value HHHH (one to four hex digits)
              \UHHHHHHHH
                     the Unicode (ISO/IEC 10646) character whose value is the hexadecimal 
                     value HHHHHHHH (one to eight hex digits)
enable [-a] [-dnps] [-f filename] [name ...]
              Enable and disable builtin shell commands.  Disabling a builtin allows a disk 
              command which has the same name as a shell builtin to be executed without 
              specifying a full pathname, even though the shell normally searches for 
              builtins before disk commands.  If -n is used, each name is disabled; 
              otherwise, names are enabled.  For example, to use the  test  binary  found
              via  the  PATH instead of the shell builtin version, run ``enable -n test''.  
              The -f option means to load the new builtin command name from shared object 
              filename, on systems that support dynamic loading.  The -d option will delete 
              a builtin previously loaded with -f.  If no name arguments are given, or if 
              the -p option is supplied, a  list  of  shell  builtins  is printed.   With no 
              other option arguments, the list consists of all enabled shell builtins.  If -
              n is supplied, only disabled builtins are printed.  If -a is supplied, the 
              list printed includes all builtins, with an indication of whether or not each 
              is enabled.  If -s is supplied, the output is restricted to the POSIX special 
              builtins.  The return value is 0 unless a name is not a shell builtin or there 
              is an error loading a new builtin from a shared object.
eval [arg ...]
              The args are read and concatenated together into a single command.  This 
              command is then read and executed by the shell, and its exit status is 
              returned as the value of eval.  If there are no args, or only null arguments, 
              eval returns 0.
exec [-cl] [-a name] [command [arguments]]
              If command is specified, it replaces the shell.  No new process is created.  
              The arguments become the arguments to command.  If the -l option is supplied, 
              the shell places  a  dash  at the  beginning  of  the  zeroth argument passed 
              to command.  This is what login(1) does.  The -c option causes command to be 
              executed with an empty environment.  If -a is supplied, the shell passes name 
              as the zeroth argument to the executed command.  If command cannot be executed 
              for some reason, a non-interactive shell exits, unless the  shell  option  
              execfail  is enabled,  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.  
              If there is a redirection error, the return status is 1.
exit [n]
              Cause the shell to exit with a status of n.  If n is omitted, the exit status 
              is that of the last command executed.  A trap on EXIT is executed before the 
              shell terminates.
export [-fn] [name[=word]] ...
export -p
              The supplied names are marked for automatic export to the environment of 
              subsequently executed commands.  If the -f option is given, the names refer to  
              functions.   If  no  names  are given,  or  if  the -p option is supplied, a 
              list of all names that are exported in this shell is printed.  The -n option 
              causes the export property to be removed from each name.  If a variable name 
              is followed by =word, the value of the variable is set to word.  export 
              returns an exit status of 0 unless an invalid option is encountered, one of 
              the  names  is  not  a valid shell variable name, or -f is supplied with a 
              name that is not a function.
fc [-e ename] [-lnr] [first] [last]
fc -s [pat=rep] [cmd]
              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 option suppresses the command numbers when listing.  The -r option 
              reverses the order of the commands.  If the -l option is given, the commands 
              are listed  on  standard  output.
              Otherwise, the editor given by ename is invoked on a file containing those 
              commands.  If ename is not given, the value of the FCEDIT variable is used, 
              and the value of EDITOR if FCEDIT is not set.  If neither variable is set, 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 invalid option is 
              encountered or first or last specify history lines out of range.  If the -e 
              option is supplied, the return value is the value of the last command executed 
              or failure if an error occurs with the temporary file of commands.  If the 
              second form is used, the return status is that of the command re-executed, 
              unless cmd does not specify a valid history line, in which case fc returns 
              failure.
fg [jobspec]
              Resume  jobspec  in  the  foreground,  and  make it the current job.  If 
              jobspec is not present, the shell's notion of the current job is used.  The 
              return value is that of the command placed into the foreground, or failure if 
              run when job control is disabled or, when run with job control enabled, if 
              jobspec does not specify a valid job or  jobspec  specifies  a  job that was 
              started without job control.
getopts optstring name [args]
              getopts  is  used  by  shell procedures to parse positional parameters.  
              optstring contains the option characters to be recognized; if a character is 
              followed by a colon, the option is expected to have an argument, which should 
              be separated from it by white space.  The colon and question mark characters 
              may not be used as option characters.  Each time it is  invoked, getopts  
              places the next option in the shell variable name, initializing name if it 
              does not exist, and the index of the next argument to be processed into the 
              variable OPTIND.  OPTIND is initialized to 1 each time the shell or a shell 
              script is invoked.  When an option requires an argument, getopts places that 
              argument into the variable OPTARG.  The shell  does  not reset OPTIND 
              automatically; it must be manually reset between multiple calls to getopts 
              within the same shell invocation if a new set of parameters is to be used.

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

              getopts normally parses the positional parameters, but if more arguments are 
              given in args, getopts parses those instead.

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

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

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

              getopts returns true if an option, specified or unspecified, is found.  It 
              returns false if the end of options is encountered or an error occurs.
hash [-lr] [-p filename] [-dt] [name]
              Each  time  hash is invoked, the full pathname of the command name is 
              determined by searching the directories in $PATH and remembered.  Any 
              previously-remembered pathname is discarded.
              If the -p option is supplied, no path search is performed, and filename is 
              used as the full file name of the command.  The -r option causes the shell to  
              forget  all  remembered  locations.   The  -d option causes the shell to 
              forget the remembered location of each name.  If the -t option is supplied, 
              the full pathname to which each name corresponds is printed.  If multiple name 
              arguments are supplied with -t, the name is printed before the hashed full 
              pathname.  The -l option causes output to be displayed in a format that may be 
              reused as input.
              If  no  arguments  are given, or if only -l is supplied, information about 
              remembered commands is printed.  The return status is true unless a name is 
              not found or an invalid option is supplied.
help [-dms] [pattern]
              Display helpful information about builtin commands.  If pattern is specified, 
              help gives detailed help on all commands matching pattern; otherwise help for 
              all the builtins  and  shell control structures is printed.
              -d     Display a short description of each pattern
              -m     Display the description of each pattern in a manpage-like format
              -s     Display only a short usage synopsis for each pattern

              The return status is 0 unless no command matches pattern.
history [n]
history -c
history -d offset
history -anrw [filename]
history -p arg [arg ...]
history -s arg [arg ...]
              With  no  options,  display the command history list with line numbers.  Lines 
              listed with a * have been modified.  An argument of n lists only the last n 
              lines.  If the shell variable HISTTIMEFORMAT is set and not null, it is used 
              as a format string for strftime(3) to display the time stamp associated with 
              each displayed  history  entry.   No  intervening  blank  is printed between 
              the formatted time stamp and the history line.  If filename is supplied, it is 
              used as the name of the history file; if not, the value of HISTFILE is used.  
              Options, if supplied, have the following meanings:
              -c     Clear the history list by deleting all the entries.
              -d offset
                     Delete the history entry at position offset.
              -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.
              -p     Perform  history  substitution  on the following args and display the 
                     result on the standard output.  Does not store the results in the 
                     history list.  Each arg must be quoted to disable normal history 
                     expansion.
              -s     Store the args in the history list as a single entry.  The last command 
                     in the history list is removed before the args are added.

              If the HISTTIMEFORMAT variable is set, the time stamp information associated 
              with each history entry is written to the history file, marked with the 
              history  comment  character.   When the  history  file  is read, lines 
              beginning with the history comment character followed immediately by a digit 
              are interpreted as timestamps for the previous history line.  The return
              value is 0 unless an invalid option is encountered, an error occurs while 
              reading or writing the history file, an invalid offset is supplied as an 
              argument to -d, or the history expansion supplied as an argument to -p fails.
jobs [-lnprs] [ jobspec ... ]
jobs -x command [ args ... ]
              The first form lists the active jobs.  The options have the following 
              meanings:
              -l     List process IDs in addition to the normal information.
              -n     Display information only about jobs that have changed status since the 
                     user was last notified of their status.
              -p     List only the process ID of the job's process group leader.
              -r     Restrict output to running jobs.
              -s     Restrict output to stopped jobs.

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

              If  the -x option is supplied, jobs replaces any jobspec found in command or 
              args with the corresponding process group ID, and executes command passing it 
              args, returning its exit status.
kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
kill -l [sigspec | exit_status]
              Send the signal named by sigspec or signum to the processes named by pid or 
              jobspec.  sigspec is either a case-insensitive signal name such as SIGKILL 
              (with or without the SIG  prefix) or a signal number; signum is a signal 
              number.  If sigspec is not present, then SIGTERM is assumed.  An argument of -
              l lists the signal names.  If any arguments are supplied when -l is given, the 
              names of the signals corresponding to the arguments are listed, and the return 
              status is 0.  The exit_status argument to -l is a number specifying either a 
              signal number  or the exit status of a process terminated by a signal.  kill 
              returns true if at least one signal was successfully sent, or false if an 
              error occurs or an invalid option is encountered.
let arg [arg ...]
              Each arg is an arithmetic expression to be evaluated (see ARITHMETIC 
              EVALUATION above).  If the last arg evaluates to 0, let returns 1; 0 is 
              returned otherwise.
local [option] [name[=value] ...]
              For  each  argument,  a  local  variable named name is created, and assigned 
              value.  The option can be any of the options accepted by declare.  When local 
              is used within a function, it causes the variable name to have a visible scope 
              restricted to that function and its children.  With no operands, local writes 
              a list of local variables to the standard output.  It  is an error to use 
              local when not within a function.  The return status is 0 unless local is used 
              outside a function, an invalid name is supplied, or name is a readonly 
              variable.
logout 
              Exit a login shell.
 mapfile [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
readarray [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
              Read lines from the standard input into the indexed array variable array, or 
              from file descriptor fd if the -u option is supplied.  The variable MAPFILE is 
              the default array.  Options, if supplied, have the following meanings:
              -n     Copy at most count lines.  If count is 0, all lines are copied.
              -O     Begin assigning to array at index origin.  The default index is 0.
              -s     Discard the first count lines read.
              -t     Remove a trailing newline from each line read.
              -u     Read lines from file descriptor fd instead of the standard input.
              -C     Evaluate callback each time quantum lines are read.  The -c option 
                     specifies quantum.
              -c     Specify the number of lines read between each call to callback.

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

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

              mapfile returns successfully unless an invalid option or option argument is 
              supplied, array is invalid or unassignable, or if array is not an indexed 
              array.
popd [-n] [+n] [-n]
              Removes  entries  from  the directory stack.  With no arguments, removes the 
              top directory from the stack, and performs a cd to the new top directory.  
              Arguments, if supplied, have the following meanings:
              -n     Suppresses the normal change of directory when removing directories 
                     from the stack, so that only the stack is manipulated.
              +n     Removes the nth entry counting from the left of the list shown by dirs, 
                     starting with zero.  For example: ``popd +0'' removes the first 
                     directory, ``popd +1'' the second.
              -n     Removes the nth entry counting from the right of the list shown by 
                     dirs, starting with zero.  For example: ``popd -0'' removes the last 
                     directory, ``popd -1'' the next to last.

              If the popd command is successful, a dirs is performed as well, and the return 
              status is 0.  popd returns false if an invalid option is encountered, the 
              directory  stack  is  empty,  a non-existent directory stack entry is 
              specified, or the directory change fails.
printf [-v var] format [arguments]
              Write  the  formatted arguments to the standard output under the control of 
              the format.  The -v option causes the output to be assigned to the variable 
              var rather than being printed to the standard output.

              The format is a character string which contains three types of objects: plain 
              characters, which are simply copied to standard output, character escape 
              sequences,  which  are  converted and  copied  to  the standard output, and 
              format specifications, each of which causes printing of the next successive 
              argument.  In addition to the standard printf(1) format specifications, printf 
              interprets the following extensions:
              %b     causes printf to expand backslash escape sequences in the corresponding 
                     argument (except that \c terminates output, backslashes in \', \", and 
                     \?  are  not  removed,  and  octal escapes beginning with \0 may 
                     contain up to four digits).
              %q     causes printf to output the corresponding argument in a format that can 
                     be reused as shell input.
              %(datefmt)T
                     causes  printf  to output the date-time string resulting from using 
                     datefmt as a format string for strftime(3).  The corresponding argument 
                     is an integer representing the number of seconds since the epoch.  Two 
                     special argument values may be used: -1 represents the current time, 
                     and -2 represents the time the shell was invoked.

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

              The  format  is reused as necessary to consume all of the arguments.  If the 
              format requires more arguments than are supplied, the extra format 
              specifications behave as if a zero value or null string, as appropriate, had 
              been supplied.  The return value is zero on success, non-zero on failure.
pushd [-n] [+n] [-n]
pushd [-n] [dir]
              Adds a directory to the top of the directory stack, or rotates the stack, 
              making the new top of the stack the current working directory.  With  no  
              arguments,  exchanges  the  top  two directories and returns 0, unless the 
              directory stack is empty.  Arguments, if supplied, have the following 
              meanings:
              -n     Suppresses the normal change of directory when adding directories to 
                     the stack, so that only the stack is manipulated.
              +n     Rotates the stack so that the nth directory (counting from the left of 
                     the list shown by dirs, starting with zero) is at the top.
              -n     Rotates the stack so that the nth directory (counting from the right of 
                     the list shown by dirs, starting with zero) is at the top.
              dir    Adds dir to the directory stack at the top, making it the new current 
                     working directory.

              If  the  pushd command is successful, a dirs is performed as well.  If the 
              first form is used, pushd returns 0 unless the cd to dir fails.  With the 
              second form, pushd returns 0 unless the directory stack is empty, a non-
              existent directory stack element is specified, or the directory change to the 
              specified new current directory fails.
pwd [-LP]
              Print the absolute pathname of the current working directory.  The pathname 
              printed contains no symbolic links if the -P option is supplied or the -o 
              physical option to the set builtin command  is  enabled.   If  the -L option 
              is used, the pathname printed may contain symbolic links.  The return status 
              is 0 unless an error occurs while reading the name of the current directory or 
              an invalid option is supplied.
read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] 
     [-t timeout] [-u fd] [name ...]
              One line is read from the standard input, or from the file descriptor fd 
              supplied as an argument to the -u option, and the first word is assigned to 
              the first name, the second word  to the second name, and so on, with leftover 
              words and their intervening separators assigned to the last name.  If there 
              are fewer words read from the input stream than names, the remaining names are 
              assigned empty values.  The characters in IFS are used to split the line into 
              words.  The backslash character (\) may be used to remove any special meaning 
              for  the  next character read and for line continuation.  Options, if 
              supplied, have the following meanings:
              -a aname
                     The words are assigned to sequential indices of the array variable 
                     aname, starting at 0.  aname is unset before any new values are 
                     assigned.  Other name arguments are ignored.
              -d delim
                     The first character of delim is used to terminate the input line, 
                     rather than newline.
              -e     If the standard input is coming from a terminal, readline (see READLINE 
                     above) is used to obtain the line.  Readline uses the current (or 
                     default, if line editing was not previously active) editing settings.
              -i text
                     If readline is being used to read the line, text is placed into the 
                     editing buffer before editing begins.
              -n nchars
                     read returns after reading nchars characters rather than waiting for a 
                     complete line of input, but honor a delimiter if fewer than nchars 
                     characters are read before  the  delimiter.
              -N nchars
                     read returns after reading exactly nchars characters rather than 
                     waiting for a complete line of input, unless EOF is encountered or read 
                     times out.  Delimiter characters encountered in the input are not 
                     treated specially and do not cause read to return until nchars 
                     characters are read.
              -p prompt
                     Display prompt on standard error, without a trailing newline, before 
                     attempting to read any input.  The prompt is displayed only if input is 
                     coming from a terminal.
              -r     Backslash does not act as an escape character.  The backslash is 
                     considered to be part of the line.  In particular, a backslash-newline 
                     pair may not be used as a line  continuation.
              -s     Silent mode.  If input is coming from a terminal, characters are not 
                     echoed.
              -t timeout
                     Cause  read  to  time out and return failure if a complete line of 
                     input is not read within timeout seconds.  timeout may be a decimal 
                     number with a fractional portion following the decimal point.  This 
                     option is only effective if read is reading input from a terminal, 
                     pipe, or other special file; it has no effect when reading from  
                     regular  files.   If timeout is 0, read returns success if input is 
                     available on the specified file descriptor, failure otherwise.  The 
                     exit status is greater than 128 if the timeout is exceeded.
              -u fd  Read input from file descriptor fd.

              If no names are supplied, the line read is assigned to the variable REPLY.  
              The return code is zero, unless end-of-file is encountered, read times out (in 
              which case the return code is greater than 128), or an invalid file descriptor 
              is supplied as the argument to -u.
readonly [-aAf] [-p] [name[=word] ...]
              The given names are marked readonly; the values of these names may not be 
              changed by subsequent assignment.  If the -f option is supplied, the functions 
              corresponding to the names  are so  marked.   The  -a option restricts the 
              variables to indexed arrays; the -A option restricts the variables to 
              associative arrays.  If both options are supplied, -A takes precedence.
              If no name arguments are given, or if the -p option is supplied, a list of all 
              readonly names is printed.  The other options may be used to restrict the 
              output to a subset of  the  set of  readonly  names.  The -p option causes 
              output to be displayed in a format that may be reused as input.  If a variable 
              name is followed by =word, the value of the variable is set to word.  The 
              return status is 0 unless an invalid option is encountered, one of the names 
              is not a valid shell variable name, or -f is supplied with a name that is not 
              a function.
return [n]
              Causes a function to 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.  Any command 
              associated with  the RETURN trap is executed before execution resumes after 
              the function or script.
set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
              Without  options, the name and value of each shell variable are displayed in a 
              format that can be reused as input for setting or resetting the currently-set 
              variables.  Read-only variables cannot be reset.  In posix mode, only shell 
              variables are listed.  The output is sorted according to the current locale.  
              When options are specified,  they  set  or  unset  shell attributes.  Any 
              arguments remaining after option processing are treated as values for the 
              positional parameters and are assigned, in order, to $1, $2, ...  $n.  
              Options, if specified, have the following meanings:
              -a      Automatically mark variables and functions which are modified or 
                      created for export to the environment of subsequent commands.
              -b      Report the status of terminated background jobs immediately, rather 
                      than before the next primary prompt.  This is effective only when job 
                      control is enabled.
              -e      Exit immediately if a pipeline (which may consist of a single simple 
                      command),  a subshell command enclosed in parentheses, or one of the 
                      commands executed as part of a command list  enclosed by braces (see 
                      SHELL GRAMMAR above) exits with a non-zero status.  The shell does not 
                      exit if the command that fails is part of the command list immediately 
                      following a while or until keyword, part of the test following the if 
                      or elif reserved words, part of any command executed in a && or || 
                      list  except  the  command  following  the final  &&  or ||, any 
                      command in a pipeline but the last, or if the command's return value 
                      is being inverted with !.  A trap on ERR, if set, is executed before 
                      the shell exits.
                      This option applies to the shell environment and each subshell 
                      environment separately (see COMMAND EXECUTION ENVIRONMENT above), and 
                      may cause subshells to exit before  executing all the commands in the 
                      subshell.
              -f      Disable pathname expansion.
              -h      Remember the location of commands as they are looked up for execution.  
                      This is enabled by default.
              -k      All arguments in the form of assignment statements are placed in the 
                      environment for a command, not just those that precede the command 
                      name.
              -m      Monitor  mode.   Job control is enabled.  This option is on by default 
                      for interactive shells on systems that support it (see JOB CONTROL 
                      above).  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 by interactive 
                      shells.
              -o option-name
                      The option-name can be one of the following:
                      allexport
                              Same as -a.
                      braceexpand
                              Same as -B.
                      emacs   Use an emacs-style command line editing interface.  This is 
                              enabled by default when the shell is interactive, unless the 
                              shell is started with the  --noediting  option.
                              This also affects the editing interface used for read -e.
                      errexit Same as -e.
                      errtrace
                              Same as -E.
                      functrace
                              Same as -T.
                      hashall Same as -h.
                      histexpand
                              Same as -H.
                      history Enable command history, as described above under HISTORY.  
                              This option is on by default in interactive shells.
                      ignoreeof
                              The effect is as if the shell command ``IGNOREEOF=10'' had 
                              been executed (see Shell Variables above).
                      keyword Same as -k.
                      monitor Same as -m.
                      noclobber
                              Same as -C.
                      noexec  Same as -n.
                      noglob  Same as -f.
                      nolog   Currently ignored.
                      notify  Same as -b.
                      nounset Same as -u.
                      onecmd  Same as -t.
                      physical
                              Same as -P.
                      pipefail
                              If  set,  the  return value of a pipeline is the value of the 
                              last (rightmost) command to exit with a non-zero status, or 
                              zero if all commands in the pipeline exit successfully.  This 
                              option is disabled by default.
                      posix   Change the behavior of bash where the default operation 
                              differs from the POSIX standard to match the standard (posix 
                              mode).
                      privileged
                              Same as -p.
                      verbose Same as -v.
                      vi      Use a vi-style command line editing interface.  This also 
                              affects the editing interface used for read -e.
                      xtrace  Same as -x.

                      If -o is supplied with no option-name, the values of the current 
                      options are printed.  If +o is supplied with no option-name, a series 
                      of set commands to recreate  the  current option settings is displayed 
                      on the standard output.
              -p      Turn  on  privileged  mode.   In this mode, the $ENV and $BASH_ENV 
                      files are not processed, shell functions are not inherited from the 
                      environment, and the SHELLOPTS, BASHOPTS, CDPATH, and GLOBIGNORE 
                      variables, if they appear in the environment, are ignored.  If the 
                      shell is started with the effective user (group) id not equal to the 
                      real user (group) id,  and  the  -p  option is not supplied, these 
                      actions are taken and the effective user id is set to the real user 
                      id.  If the -p option is supplied at startup, the effective
                      user id is not reset.  Turning this option off causes the effective 
                      user and group ids to be set to the real user and group ids.
              -t      Exit after reading and executing one command.
              -u      Treat unset variables and parameters other than the special parameters 
                      "@" and "*" as an error when performing parameter expansion.  If 
                      expansion is attempted on an unset variable or parameter, the shell 
                      prints an error message, and, if not interactive, exits with a non-
                      zero status.
              -v      Print shell input lines as they are read.
              -x      After  expanding  each  simple command, for command, case command, 
                      select command, or arithmetic for command, display the expanded value 
                      of PS4, followed by the command and its
                      expanded arguments or associated word list.
              -B      The shell performs brace expansion (see Brace Expansion above).  This 
                      is on by default.
              -C      If set, bash does not overwrite an existing file with the >, >&, and 
                      <> redirection operators.  This may be overridden when creating output 
                      files by using the redirection operator >| instead of >.
              -E      If set, any trap on ERR is inherited by shell functions, command 
                      substitutions, and commands executed in a subshell environment.  The 
                      ERR trap is normally not inherited in such cases.
              -H      Enable !  style history substitution.  This option is on by default 
                      when the shell is interactive.
              -P      If set, the shell does not follow symbolic links when executing 
                      commands such as cd that change the current  working  directory.   It  
                      uses  the  physical  directory  structure instead.  By default, bash 
                      follows the logical chain of directories when performing commands 
                      which change the current directory.
              -T      If  set, any traps on DEBUG and RETURN are inherited by shell 
                      functions, command substitutions, and commands executed in a subshell 
                      environment.  The DEBUG and RETURN traps are normally not inherited in 
                      such cases.
              --      If no arguments follow this option, then the positional parameters are 
                      unset.  Otherwise, the positional parameters are set to the args, even 
                      if some of them begin with a -.
              -       Signal the end of options, cause all remaining args to be assigned to 
                      the positional parameters.  The -x and -v options are turned off.  If 
                      there are no  args,  the  positional parameters remain unchanged.

              The options are off by default unless otherwise noted.  Using + rather than - 
              causes these options to be turned off.  The options can also be specified as 
              arguments to an invocation of the shell.  The current set of options may be 
              found in $-.  The return status is always true unless an invalid option is 
              encountered.
shift [n]
              The positional parameters from n+1 ... are renamed to $1 ....  Parameters 
              represented by the numbers $# down to $#-n+1 are unset.  n must be a non-
              negative number less than or equal to $#.  If n is 0, no parameters are 
              changed.  If n is not given, it is assumed to be 1.  If n is greater than $#, 
              the positional parameters are not changed.  The return status is greater than 
              zero if n is greater than $# or less than zero; otherwise 0.
shopt [-pqsu] [-o] [optname ...]
              Toggle the values of variables controlling optional shell behavior.  With no 
              options, or with the -p option, a list of all settable options is displayed, 
              with an indication of  whether or not each is set.  The -p option causes 
              output to be displayed in a form that may be reused as input.  Other options 
              have the following meanings:
              -s     Enable (set) each optname.
              -u     Disable (unset) each optname.
              -q     Suppresses  normal  output  (quiet mode); the return status indicates 
                     whether the optname is set or unset.  If multiple optname arguments are 
                     given with -q, the return status is zero if all optnames are enabled; 
                     non-zero otherwise.
              -o     Restricts the values of optname to be those defined for the -o option 
                     to the set builtin.

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

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

              The list of shopt options is:

              autocd  If set, a command name that is the name of a directory is executed as 
                      if it were the argument to the cd command.  This option is only used 
                      by interactive shells.
              cdable_vars
                      If set, an argument to the cd builtin command that is not a directory 
                      is assumed to be the name of a variable whose value is the directory 
                      to change to.
              cdspell If set, minor errors in the spelling of a directory component in a cd 
                      command will be corrected.  The errors checked for are transposed 
                      characters, a missing character, and one character too many.  If a 
                      correction is found, the corrected file name is printed, and the 
                      command proceeds.  This option is only used by interactive shells.
              checkhash
                      If set, bash checks that a command found in the hash table exists 
                      before trying to execute it.  If a hashed command no longer exists, a 
                      normal path search is performed.
              checkjobs
                      If  set, bash lists the status of any stopped and running jobs before 
                      exiting an interactive shell.  If any jobs are running, this causes 
                      the exit to be deferred until a second exit is attempted without an 
                      intervening command (see JOB CONTROL above).  The shell always 
                      postpones exiting if any jobs are stopped.
              checkwinsize
                      If set, bash checks the window size after each command and, if 
                      necessary, updates the values of LINES and COLUMNS.
              cmdhist If set, bash attempts to save all lines of a multiple-line command in 
                      the same history entry.  This allows easy re-editing of multi-line 
                      commands.
              compat31
                      If set, bash changes its behavior to that of version 3.1 with respect 
                      to quoted arguments to the [[ conditional command's =~ operator.
              compat32
                      If set, bash changes its behavior to that of version 3.2 with respect 
                      to locale-specific string comparison when using the [[ conditional 
                      command's < and > operators.  Bash versions prior to bash-4.1 use 
                      ASCII collation and strcmp(3); bash-4.1 and later use the current 
                      locale's collation sequence and strcoll(3).
              compat40
                      If set, bash changes its behavior to that of version 4.0 with respect 
                      to locale-specific string comparison when using the [[ conditional 
                      command's < and > operators (see previous item) and the effect of 
                      interrupting a command list.
              compat41
                      If set, bash, when in posix mode, treats a single quote in a double-
                      quoted parameter expansion as a special character.  The single quotes 
                      must match (an even  number)  and  the characters between the single 
                      quotes are considered quoted.  This is the behavior of posix mode 
                      through version 4.1.  The default bash behavior remains as in previous 
                      versions.
              direxpand
                      If set, bash replaces directory names with the results of word 
                      expansion when performing filename completion.  This changes the 
                      contents of the readline editing buffer.  If not set, bash attempts to 
                      preserve what the user typed.
              dirspell
                      If set, bash attempts spelling correction on directory names during 
                      word completion if the directory name initially supplied does not 
                      exist.
              dotglob If set, bash includes filenames beginning with a `.' in the results of 
                      pathname expansion.
              execfail
                      If set, a non-interactive shell will not exit if it cannot execute the 
                      file specified as an argument to the exec builtin command.  An 
                      interactive shell does not  exit  if  exec fails.
              expand_aliases
                      If set, aliases are expanded as described above under ALIASES.  This 
                      option is enabled by default for interactive shells.
              extdebug
                      If set, behavior intended for use by debuggers is enabled:
                      1.     The -F option to the declare builtin displays the source file 
                             name and line number corresponding to each function name 
                             supplied as an argument.
                      2.     If the command run by the DEBUG trap returns a non-zero value, 
                             the next command is skipped and not executed.
                      3.     If  the  command  run  by the DEBUG trap returns a value of 2, 
                             and the shell is executing in a subroutine (a shell function or 
                             a shell script executed by the . or source builtins), a call to 
                             return is simulated.
                      4.     BASH_ARGC and BASH_ARGV are updated as described in their 
                             descriptions above.
                      5.     Function tracing is enabled:  command substitution, shell 
                             functions, and subshells invoked with ( command ) inherit the 
                             DEBUG and RETURN traps.
                      6.     Error tracing is enabled:  command substitution, shell 
                             functions, and subshells invoked with ( command ) inherit the 
                             ERR trap.
              extglob If set, the extended pattern matching features described above under 
                      Pathname Expansion are enabled.
              extquote
                      If set, $'string' and $"string" quoting is performed within 
                      ${parameter} expansions enclosed in double quotes.  This option is 
                      enabled by default.
              failglob
                      If set, patterns which fail to match filenames during pathname 
                      expansion result in an expansion error.
              force_fignore
                      If set, the suffixes specified by the FIGNORE shell variable cause 
                      words to be ignored when performing word completion even if the 
                      ignored words are the only  possible  completions.  See SHELL 
                      VARIABLES above for a description of FIGNORE.  This option is enabled 
                      by default.
              globstar
                      If  set,  the  pattern  **  used  in a pathname expansion context will 
                      match all files and zero or more directories and subdirectories.  If 
                      the pattern is followed by a /, only directories and subdirectories 
                      match.
              gnu_errfmt
                      If set, shell error messages are written in the standard GNU error 
                      message format.
              histappend
                      If set, the history list is appended to the file named by the value of 
                      the HISTFILE variable when the shell exits, rather than overwriting 
                      the file.
              histreedit
                      If set, and readline is being used, a user is given the opportunity to 
                      re-edit a failed history substitution.
              histverify
                      If set, and readline is being used, the results of history 
                      substitution are not immediately passed to the shell parser.  Instead, 
                      the resulting line is loaded into the readline editing buffer, 
                      allowing further modification.
              hostcomplete
                      If  set, and readline is being used, bash will attempt to perform 
                      hostname completion when a word containing a @ is being completed (see 
                      Completing under READLINE above).  This is enabled by default.
              huponexit
                      If set, bash will send SIGHUP to all jobs when an interactive login 
                      shell exits.
              interactive_comments
                      If set, allow a word beginning with # to cause that word and all 
                      remaining characters on that line to be ignored in an interactive 
                      shell (see COMMENTS above).  This  option  is enabled by default.
              lastpipe
                      If set, and job control is not active, the shell runs the last command 
                      of a pipeline not executed in the background in the current shell 
                      environment.
              lithist If set, and the cmdhist option is enabled, multi-line commands are 
                      saved to the history with embedded newlines rather than using 
                      semicolon separators where possible.
              login_shell
                      The shell sets this option if it is started as a login shell (see 
                      INVOCATION above).  The value may not be changed.
              mailwarn
                      If set, and a file that bash is checking for mail has been accessed 
                      since the last time it was checked, the message ``The mail in mailfile 
                      has been read'' is displayed.
              no_empty_cmd_completion
                      If set, and readline is being used, bash will not attempt to search 
                      the PATH for possible completions when completion is attempted on an 
                      empty line.
              nocaseglob
                      If set, bash matches filenames in a case-insensitive fashion when 
                      performing pathname expansion (see Pathname Expansion above).
              nocasematch
                      If set, bash matches patterns in a case-insensitive fashion when 
                      performing matching while executing case or [[ conditional commands.
              nullglob
                      If set, bash allows patterns which match no files (see Pathname 
                      Expansion above) to expand to a null string, rather than themselves.
              progcomp
                      If set, the programmable completion facilities (see Programmable 
                      Completion above) are enabled.  This option is enabled by default.
              promptvars
                      If  set,  prompt  strings undergo parameter expansion, command 
                      substitution, arithmetic expansion, and quote removal after being 
                      expanded as described in PROMPTING above.  This option is enabled by 
                      default.
              restricted_shell
                      The shell sets this option if it is started in restricted mode (see 
                      RESTRICTED SHELL below).  The value may not be changed.  This is not 
                      reset when the startup files  are  executed, allowing the startup 
                      files to discover whether or not a shell is restricted.
              shift_verbose
                      If set, the shift builtin prints an error message when the shift count 
                      exceeds the number of positional parameters.
              sourcepath
                      If set, the source (.) builtin uses the value of PATH to find the 
                      directory containing the file supplied as an argument.  This option is 
                      enabled by default.
              xpg_echo
                      If set, the echo builtin expands backslash-escape sequences by 
                      default.
suspend [-f]
              Suspend  the  execution of this shell until it receives a SIGCONT signal. When 
              the suspended shell is a background process, it can be restarted by the fg 
              command. For more information, read the JOB CONTROL section. The suspend 
              command can not suspend the login shell. However, when -f option is specified, 
              suspend command can suspend even login shell.  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 or 1 depending on the evaluation of the conditional 
              expression expr.  Each operator and operand must be a separate argument.  
              Expressions are composed of the primaries described above under CONDITIONAL 
              EXPRESSIONS.  test does not accept any options, nor does it accept and ignore 
              an argument of -- as signifying the end of options.

              Expressions may be combined using the following operators, listed in 
              decreasing order of precedence.  The evaluation depends on the number of 
              arguments; see below.  Operator precedence is used when there are five or more 
              arguments.

              ! expr True if expr is false.
              ( expr )
                     Returns the value of expr.  This may be used to override the normal 
                     precedence of operators.
              expr1 -a expr2
                     True if both expr1 and expr2 are true.
              expr1 -o expr2
                     True if either expr1 or expr2 is true.

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

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

              When used with test or [, the < and > operators sort lexicographically using 
              ASCII ordering.
times  Print the accumulated user and system times for the shell and for processes run from 
       the shell.  The return status is 0.
trap [-lp] [[arg] sigspec ...]
              The command arg is to be read and executed when the shell receives signal(s) 
              sigspec.  If arg is absent (and there is a single sigspec) or -, each 
              specified  signal  is  reset  to  its original  disposition  (the  value  it  
              had  upon entrance to the shell).  If arg is the null string the signal 
              specified by each sigspec is ignored by the shell and by the commands it 
              invokes.  If arg is not present and -p has been supplied, then the trap 
              commands associated with each sigspec are displayed.  If no arguments are 
              supplied or if only -p is given,  trap prints the list of commands associated 
              with each signal.  The -l option causes the shell to print a list of signal 
              names and their corresponding numbers.  Each sigspec is either a signal name 
              defined in <signal.h>, or a signal number.  Signal names are case insensitive 
              and the SIG prefix is optional.

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

              If  a sigspec is ERR, the command arg is executed whenever a simple command 
              has a non-zero exit status, subject to the following conditions.  The ERR trap 
              is not executed if the failed command is part of the command list immediately 
              following a while or until keyword, part of the test in an if statement, part 
              of a command executed in a && or || list, or if  the  command's return value 
              is being inverted via !.  These are the same conditions obeyed by the errexit 
              option.

              Signals  ignored  upon  entry  to the shell cannot be trapped, reset or 
              listed.  Trapped signals that are not being ignored are reset to their 
              original values in a subshell or subshell environment when one is created.  
              The return status is false if any sigspec is invalid; otherwise trap returns 
              true.
type [-aftpP] name [name ...]
              With no options, indicate how each name would be interpreted if used as a 
              command name.  If the -t option is used, type prints a string  which  is  one  
              of  alias,  keyword,  function, builtin,  or  file  if  name  is an alias, 
              shell reserved word, function, builtin, or disk file, respectively.  If the 
              name is not found, then nothing is printed, and an exit status of false is 
              returned.  If the -p option is used, type either returns the name of the disk 
              file that would be executed if name were specified as a command name, or  
              nothing  if  ``type  -t name''  would  not  return  file.  The -P option 
              forces a PATH search for each name, even if ``type -t name'' would not return 
              file.  If a command is hashed, -p and -P print the hashed value, not 
              necessarily the file that appears first in PATH.  If the -a option is used, 
              type prints all of the places that contain an executable named name.  This 
              includes  aliases  and functions,  if  and  only  if the -p option is not also 
              used.  The table of hashed commands is not consulted when using -a.  The -f 
              option suppresses shell function lookup, as with the command builtin.  type 
              returns true if all of the arguments are found, false if any are not found.
ulimit [-HSTabcdefilmnpqrstuvx [limit]]
              Provides control over the resources available to the shell and to processes 
              started by it, on systems that allow such control.  The -H and -S options 
              specify  that  the  hard  or  soft limit  is  set for the given resource.  A 
              hard limit cannot be increased by a non-root user once it is set; a soft limit 
              may be increased up to the value of the hard limit.  If neither -H nor -S is 
              specified, both the soft and hard limits are set.  The value of limit can be a 
              number in the unit specified for the resource or one of the special values  
              hard,  soft,  or unlimited,  which  stand  for  the  current hard limit, the 
              current soft limit, and no limit, respectively.  If limit is omitted, the 
              current value of the soft limit of the resource is printed, unless the -H 
              option is given.  When more than one resource is specified, the limit name and 
              unit are printed before the value.  Other options are interpreted as follows:
              -a     All current limits are reported
              -b     The maximum socket buffer size
              -c     The maximum size of core files created
              -d     The maximum size of a process's data segment
              -e     The maximum scheduling priority ("nice")
              -f     The maximum size of files written by the shell and its children
              -i     The maximum number of pending signals
              -l     The maximum size that may be locked into memory
              -m     The maximum resident set size (many systems do not honor this limit)
              -n     The maximum number of open file descriptors (most systems do not allow 
                     this value to be set)
              -p     The pipe size in 512-byte blocks (this may not be set)
              -q     The maximum number of bytes in POSIX message queues
              -r     The maximum real-time scheduling priority
              -s     The maximum stack size
              -t     The maximum amount of cpu time in seconds
              -u     The maximum number of processes available to a single user
              -v     The maximum amount of virtual memory available to the shell and, on 
                     some systems, to its children
              -x     The maximum number of file locks
              -T     The maximum number of threads

              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 -T, -b, -n, and -u, which are 
              unscaled values.  The return status is 0 unless an invalid option or argument 
              is supplied, or an error occurs while setting a new limit.  In POSIX Mode 512-
              byte blocks are used for the `-c' and `-f' options.
umask [-p] [-S] [mode]
              The user file-creation mask is set to mode.  If mode begins with a digit, it 
              is interpreted as an octal number; otherwise it is interpreted as a symbolic  
              mode  mask  similar  to  that accepted  by chmod(1).  If mode is omitted, the 
              current value of the mask is printed.  The -S option causes the mask to be 
              printed in symbolic form; the default output is an octal number.  If the -p 
              option is supplied, and mode is omitted, the output is in a form that may be 
              reused as input.  The return status is 0 if the mode was successfully changed 
              or if no mode argument was supplied, and false otherwise.
unalias [-a] [name ...]
              Remove each name from the list of defined aliases.  If -a is supplied, all 
              alias definitions are removed.  The return value is true unless a supplied 
              name is not a defined alias.
unset [-fv] [name ...]
              For each name, remove the corresponding variable or function.  If no options 
              are supplied, or the -v option is given, each name refers to a shell variable.  
              Read-only variables may not be unset.  If -f is specified, each name refers to 
              a shell function, and the function definition is removed.  Each unset variable 
              or function is removed from the environment passed  to subsequent  commands.  
              If any of COMP_WORDBREAKS, RANDOM, SECONDS, LINENO, HISTCMD, FUNCNAME, GROUPS, 
              or DIRSTACK are unset, they lose their special properties, even if they are 
              subsequently reset.  The exit status is true unless a name is readonly.
wait [n ...]
              Wait for each specified process and return its termination status.  Each 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-existent process or job, the return status is 127.  Otherwise, 
              the return status is the exit status of the last process or job waited for.
SEE ALSO
       bash(1), sh(1)


GNU Bash-4.0                    2004 Apr 20                       BASH_BUILTINS(1)