Skip to main content



       bash,  :,  ., [, alias, bg, bind, break, builtin, cd, command, compgen,
       complete, continue, declare, dirs, disown, echo, enable,  eval, exec,
       exit,  export,  fc,  fg, getopts, hash, help, history, jobs, kill, let,
       local, logout, popd, printf, pushd, pwd, read, readonly, return,  set,
       shift,  shopt,  source, suspend,  test, times, trap, type, typeset,
       ulimit, umask, unalias, unset,  wait  - bash  built-in commands,  see
       Unless otherwise noted, each builtin command documented in this section
       as accepting options preceded by - accepts -- to signify the end of the
       options.  For  example, the  :, true, false, and test builtins do not
       accept options. Also, please note that while executing in non-interac-
       tive  mode  and while  in  posix mode, any special builtin (like ., :,
       break, continue, eval,  exec,  exit,  export,  readonly, return,  set,
       shift,  source, times, trap,  unset)  exiting with a non-zero status
       causes the shell to stop execution.
       : [arguments]
     No effect; the command does nothing beyond  expanding  arguments
     and  performing any specified redirections.  A zero exit code is

.  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 exe-
     cuted from filename.  If filename does not contain a slash, file
     names  in PATH  are used to find the directory containing file-
     name.  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 posi-
     tional  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  sup-
     plied,  the  name and  value  of the  alias is printed. Alias
     returns true unless a name is given for which no alias has  been

     Note  aliases  are  not  expanded by default in non-interactive
     shell, and it can be enabled by setting the expand_aliases shell
     option using shopt.

       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-stan-
    dard,  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.
     -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.
     -s     Display  readline key  sequences bound to macros and the
    strings they output in such a way that they  can  be  re-
     -S     Display  readline key  sequences bound to macros and the
    strings they output.
     -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

     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 func-
     tionality 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.

       cd [-L|-P] [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 fol-
     lowed.  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  success-
     fully changed; false otherwise.

       caller [expr]
     Returns the context of any active subroutine call (a shell func-
     tion or a script executed with the . or source builtins. With-
     out expr, caller displays the line number and source filename of
     the current subroutine call.  If a non-negative integer is  sup-
     plied 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 sub-
     routine call or expr does not correspond to a valid position  in
     the call stack.

       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 can-
     not be found, the exit status is 127.  Otherwise, the exit  sta-
     tus 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  pro-
     grammable completion  code  had generated them directly from a
     completion specification with the same flags.  If word is speci-
     fied, 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] [-A action] [-G globpat]  [-W
       wordlist] [-P prefix] [-S suffix]
     [-X filterpat] [-F function] [-C command] name [name ...]
       complete -pr [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 spec-
     ification for each name, or, if no names are supplied, all  com-
     pletion specifications.

     The  process  of applying  these completion specifications when
     word completion is  attempted  is described  above  under  Pro-
     grammable 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 expan-
     sion before the complete builtin is invoked.
     -o comp-option
     The comp-option controls several aspects of  the comp-
     spec’s  behavior beyond the simple generation of comple-
     tions.  comp-option may be one of:
     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.
     Perform directory name completion if  the comp-
     spec generates no matches.
     Tell  readline that the compspec generates file-
     names, so it can perform any  filename-specific
     processing  (like adding a  slash to directory
     names 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
     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.
     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 names. May also be specified as -d.
     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.
     Names of shell functions.
     group   Group names.  May also be specified as -g.
     Help topics as accepted by the help builtin.
     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
     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
     shopt   Shell option names  as  accepted by  the shopt
     signal  Signal names.
     stopped Names of stopped jobs, if job control is active.
     user    User names.  May also be specified as -u.
     Names of all shell variables.  May also be spec-
     ified as -v.
     -G globpat
     The  filename  expansion pattern globpat is expanded to
     generate the possible completions.
     -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 com-
     -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  com-
     pletions are  retrieved from the value of the COMPREPLY
     array variable.
     -X filterpat
     filterpat is a pattern as used for  filename  expansion.
     It is applied to the list of possible completions gener-
     ated 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.
     -P prefix
     prefix is added at the beginning of each possible  com-
     pletion after all other options have been applied.
     -S suffix
     suffix is appended to each possible completion after all
     other options have been applied.

     The return value is true unless an invalid option is  supplied,
     an  option  other than -p or -r is supplied without a name argu-
     ment, 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.

       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 [-afFirtx] [-p] [name[=value] ...]
       typeset [-afFirtx] [-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, additional options are ignored.  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 following options can be used to restrict out-
     put to variables with the specified attribute or to  give vari-
     ables attributes:
     -a     Each name is an array variable (see Arrays above).
     -f     Use function names only.
     -i     The variable is treated as an integer; arithmetic evalua-
    tion (see ARITHMETIC EVALUATION ) is performed  when  the
    variable is assigned a value.
     -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
     -x     Mark  names  for  export  to  subsequent commands via the

     Using ‘+’ instead of ‘-’ turns off the attribute instead,  with
     the  exception that +a may not be used to destroy an array vari-
     able.  When used in a function, makes each name local,  as  with
     the  local  command.   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 read-
     only  status for a readonly variable, an attempt is made to turn
     off array status for an array variable, or an attempt is made to
     display a non-existent function with -f.

       dirs [-clpv] [+n] [-n]
     Without  options, displays  the list  of  currently remembered
     directories.  The default display is  on a  single  line  with
     directory names separated by spaces.  Directories are added to
     the list with  the  pushd command;  the popd  command  removes
     entries from the list.
     +n     Displays the nth entry counting from the left of the list
    shown by dirs when invoked without options, starting with
     -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
     -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, pre-
    fixing 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 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 job-
     spec 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, interpreta-
     tion of the following backslash-escaped characters  is  enabled.
     The  -E option disables the interpretation of these escape char-
     acters, 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 trailing newline
     \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)

       enable [-adnps] [-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 argu-
     ments, the list consists of all enabled shell builtins. If  -n
     is  supplied, only disabled builtins are printed. If -a is sup-
     plied, the list printed includes all builtins, with  an  indica-
     tion  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  com-
     mand.   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 begin-
     ning of the zeroth arg 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  can-
     not  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 envi-
     ronment 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 func-

       fc [-e ename] [-nlr] [first] [last]
       fc -s [pat=rep] [cmd]
     Fix  Command.  In the first form, a range of commands from first
     to last is selected from the history list.  First and  last  may
     be  specified  as a string (to locate the last command beginning
     with that string) or as a number (an  index  into  the  history
     list, where a negative number is used as an offset from the cur-
     rent 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 spec-
     ified  it is set to the previous command for editing and -16 for

     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. Other-
     wise,  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 com-

     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-exe-
     cuted,  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 spec-
     ify  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  parame-
     ters.   optstring contains  the option characters to be recog-
     nized; 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 automati-
     cally; it must be manually  reset  between  multiple  calls  to
     getopts within the same shell invocation if a new set of parame-
     ters 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 dis-
     played, 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]
     For each name, the full file name of the command is  determined
     by searching the directories in $PATH and remembered.  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 for-
     mat 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 [-s] [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.  The -s option restricts the  information
     displayed to  a short  usage synopsis. 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 num-
     bers.  Lines listed with a * have been modified. An argument of
     n lists only the last n lines.  If the shell variable  HISTTIME-
     FORMAT  is  set  and not null, it is used as a format string for
     strftime(3) to display the time stamp associated with each  dis-
     played  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, overwrit-
    ing 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 is set, the time stamp information associ-
     ated with each history entry is written  to  the history file.
     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 fol-
     lowing meanings:
     -l     List process IDs in addition to the normal information.
     -p     List  only the  process  ID  of  the job’s process group
     -n     Display information only about  jobs  that have  changed
    status  since the user was last notified of their status.
     -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 ARITH-
     METIC EVALUATION).  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 func-
     tion 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.

       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 follow-
     ing meanings:
     +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
     -n     Suppresses the normal change of directory when  removing
    directories  from the  stack,  so that only the stack is

     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-exis-
     tent directory stack entry is specified, or the directory change

       printf [-v var] format [arguments]
     Write the formatted arguments to the standard output  under  the
     control  of  the format. 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  for-
     mat  specifications,  each  of which causes printing of the next
     successive argument.  In addition to the standard printf(1) for-
     mats,  %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), and %q causes
     printf to output the corresponding argument in a format that can
     be reused as shell input.

     The -v option causes the output to be assigned to the  variable
     var rather than being printed to the standard output.

     The  format  is  reused as necessary to consume all of the argu-
     ments.  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] [dir]
       pushd [-n] [+n] [-n]
     Adds  a  directory to the top of the directory stack, or rotates
     the stack, making the new top of the stack the  current  working
     directory.  With no arguments, exchanges the top two directories
     and returns 0, unless the directory stack is empty.   Arguments,
     if supplied, have the following meanings:
     +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.
     -n     Suppresses the  normal  change  of directory when adding
    directories to the stack, so  that  only the  stack  is
     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 direc-
     tory  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] [-u fd] [-t timeout] [-a aname] [-p prompt] [-n nchars] [-d
       delim] [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  interven-
     ing  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  fol-
     lowing 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
     -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.
     -n nchars
    read returns after reading nchars characters rather  than
    waiting for a complete line of input.
     -p prompt
    Display prompt on standard error, without a trailing new-
    line, 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 back-
    slash is considered to be part of the line.  In  particu-
    lar,  a  backslash-newline pair may not be used as a line
     -s     Silent mode.  If input is coming from a terminal, charac-
    ters 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.  This
    option  has  no  effect if read is not reading input from
    the terminal or a pipe.
     -u fd  Read input from file descriptor fd.

     If no names are supplied, the line read is assigned to the vari-
     able  REPLY.   The  return  code is zero, unless end-of-file is
     encountered, read times out, or an invalid  file descriptor  is
     supplied as the argument to -u.

       readonly [-apf] [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 arrays. If no
     name  arguments  are  given,  or if the -p option is supplied, a
     list of all readonly names is printed.   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 vari-
     able  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

       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 [--abefhkmnptuvxBCHP] [-o option] [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 can-
     not  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 the options are processed are  treated
     as  values  for  the  positional parameters and are assigned, in
     order, to $1, $2, ...  $n.  Options, if specified, have the fol-
     lowing 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 immedi-
     ately, rather than before the next primary prompt.  This
     is effective only when job control is enabled.
     -e      Exit  immediately if a simple command (see SHELL GRAMMAR
     above) exits with a non-zero status.  The shell does not
     exit  if the  command that fails is part of the command
     list immediately following a  while  or  until  keyword,
     part  of the test in an if statement, part of a && or ││
     list, or if the command’s return value is being inverted
     via  !. A  trap on ERR, if set, is executed before the
     shell exits.
     -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 pro-
     cesses run in a separate process group and a  line  con-
     taining  their exit status is printed upon their comple-
     -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:
     Same as -a.
     Same as -B.
     emacs   Use an emacs-style command line  editing inter-
     face.  This is enabled by default when the shell
     is interactive, unless the shell is started with
     the --noediting option.
     Same as -E.
     Same as -T.
     errexit Same as -e.
     hashall Same as -h.
     Same as -H.
     history Enable command history, as described above under
     HISTORY. This option is on by default in inter-
     active shells.
     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.
     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.
     Same as -P.
     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).
     Same as -p.
     verbose Same as -v.
     vi      Use a vi-style command line editing interface.
     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
     -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
     variable, if it appears in the environment, is  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
     -t      Exit after reading and executing one command.
     -u      Treat unset variables as an error when performing param-
     eter  expansion. If expansion is attempted on an unset
     variable, the shell prints an error message, and, if not
     interactive, exits with a non-zero status.
     -v      Print shell input lines as they are read.
     -x      After  expanding each simple command, for command, case
     command, select command, or arithmetic for command, dis-
     play  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 redi-
     rection operator >| instead of >.
     -E      If set, any trap on ERR is inherited by shell functions,
     command  substitutions,  and commands executed in a sub-
     shell environment.  The ERR trap is normally not inher-
     ited 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 parame-
     ters 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 posi-
     tional 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 encoun-

       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 behav-
     ior.  With no options, or with the -p option, a list of all set-
     table 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 fol-
     lowing 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 oth-
     -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 dis-
     play is limited to those options which are set or unset, respec-
     tively. Unless otherwise noted, the shopt options are disabled
     (unset) by default.

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

     The list of shopt options is:

     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 com-
     ponent in a cd command will be  corrected.   The errors
     checked for are transposed characters, a missing charac-
     ter, and one character too many. If  a correction  is
     found,  the corrected file name is printed, and the com-
     mand proceeds.  This option is only used by  interactive
     If set, bash checks that a command found in the hash ta-
     ble exists before trying to execute  it. If  a hashed
     command  no  longer exists, a normal path search is per-
     If set, bash checks the window size after each  command
     and,  if necessary,  updates  the  values  of LINES and
     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.
     dotglob If set, bash includes filenames beginning with a ‘.’  in
     the results of pathname expansion.
     If set, a non-interactive shell will not exit if it can-
     not execute the file specified as an  argument  to  the
     exec  builtin  command. An  interactive shell does not
     exit if exec fails.
     If set, aliases are expanded as  described  above under
     ALIASES. This option is enabled by default for interac-
     tive shells.
     If set,  behavior intended  for use  by debuggers  is
     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  sub-
    routine  (a shell function or a shell script exe-
    cuted 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  substitu-
    tion, 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 ERROR trap.
     extglob If set, the extended pattern matching features described
     above under Pathname Expansion are enabled.
     If  set, $'string'  and $"string" quoting is performed
     within  ${parameter}  expansions enclosed   in double
     quotes.  This option is enabled by default.
     If  set, patterns  which fail to match filenames during
     pathname expansion result in an expansion error.
     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 possi-
     ble  completions.  See  SHELL  VARIABLES above for  a
     description of  FIGNORE. This  option  is  enabled  by
     If set, shell error messages are written in the standard
     GNU error message format.
     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.
     If set, and readline is being used, a user is given  the
     opportunity to re-edit a failed history substitution.
     If  set, and readline is being used, the results of his-
     tory substitution are  not  immediately  passed  to  the
     shell  parser.   Instead, the  resulting line is loaded
     into the readline editing buffer, allowing further modi-
     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.
     If set, bash will send SIGHUP to all jobs when an inter-
     active login shell exits.
     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.
     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.
     The shell sets this option if it is started as  a login
     shell  (see  INVOCATION  above). The  value may not be
     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  dis-
     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.
     If  set, bash  matches  filenames in a case-insensitive
     fashion when performing pathname expansion (see Pathname
     Expansion above).
     If  set, bash  matches  patterns in a case-insensitive
     fashion when performing matching while executing case or
     [[ conditional commands.
     If  set, bash allows patterns which match no files (see
     Pathname Expansion above) to expand to  a null  string,
     rather than themselves.
     If set, the programmable completion facilities (see Pro-
     grammable Completion above) are enabled. This option is
     enabled by default.
     If set, prompt strings undergo parameter expansion, com-
     mand  substitution,  arithmetic  expansion,  and quote
     removal  after  being expanded as described in PROMPTING
     above.  This option is enabled by default.
     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 dis-
     cover whether or not a shell is restricted.
     If set, the shift builtin prints an error message  when
     the shift count exceeds the number of positional parame-
     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.
     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 com-
     mand 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.
     ! 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
     2 arguments
    If the first argument is !, the expression is true if and
    only if the second argument is null.  If the first argu-
    ment  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
     3 arguments
    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.  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.
    The -a and -o operators are considered  binary  operators
    in this case.
     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 eval-
    uated according to precedence  using  the rules listed
     5 or more arguments
    The  expression  is  parsed  and  evaluated  according to
    precedence using the rules listed above.

       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 cor-
     responding 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 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 && or ││ list, or
     if  the  command’s  return value is being inverted via !. These
     are the same conditions obeyed by the  errexit  option. If  a
     sigspec is RETURN, the command arg is executed each time a shell
     function or a script executed with the . or source builtins fin-
     ishes executing. 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 child process
     when it 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 speci-
     fied 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 func-
     tion lookup, as with the command builtin. type returns true  if
     any of the arguments are found, false if none are found.

       ulimit [-SHacdefilmnpqrstuvx [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  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 fol-
     -a     All current limits are reported
     -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
     -i     The maximum number of pending signals
     -l     The maximum size that may be locked into memory
     -m     The maximum resident set size (has no effect on Linux)
     -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
     -v     The maximum amount of virtual  memory  available  to  the
     -x     The maximum number of file locks

     If limit is given, it is the new value of the specified resource
     (the -a option is display only). If no option is given, then -f
     is  assumed.  Values are in 1024-byte increments, except for -t,
     which is in seconds, -p, which is in units of  512-byte  blocks,
     and  -n and -u, which are unscaled values.  The return status is
     0 unless an invalid option or argument is supplied, or an error
     occurs while setting a new limit.

       umask [-p] [-S] [mode]
     The user file-creation mask is set to mode.  If mode begins with
     a digit, it is interpreted as an octal number; otherwise it  is
     interpreted  as a symbolic mode mask similar to that accepted by
     chmod(1). If mode is omitted, the current value of the mask  is
     printed. The  -S  option causes the mask to be printed in sym-
     bolic 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 func-
     tion, and the function definition is removed.  Each unset vari-
     able  or function is removed from the environment passed to sub-
     sequent commands. If any of RANDOM, SECONDS,  LINENO,  HISTCMD,
     FUNCNAME, GROUPS, or DIRSTACK are unset, they lose their special
     properties, even if they are subsequently reset. The exit  sta-
     tus is true unless a name is readonly.

       wait [n ...]
     Wait  for each specified process and return its termination sta-
     tus.  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  pro-
     cesses  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.

       bash(1), sh(1)

GNU Bash-3.0  2004 Apr 20      BASH_BUILTINS(1)


Popular posts from this blog

Creating Multiple VLANs over Bonding Interfaces with Proper Routing on a Centos Linux Host

In this post, I am going to explain configuring multiple VLANs on a bond interface. First and foremost, I would like to describe the environment and give details of the infrastructure. The server has 4 Ethernet links to a layer 3 switch with names: enp3s0f0, enp3s0f1, enp4s0f0, enp4s0f1 There are two bond interfaces both configured as active-backup bond0, bond1 enp4s0f0 and enp4s0f1 interfaces are bonded as bond0. Bond0 is for making ssh connections and management only so corresponding switch ports are not configured in trunk mode. enp3s0f0 and enp3s0f1 interfaces are bonded as bond1. Bond1 is for data and corresponding switch ports are configured in trunk mode. Bond0 is the default gateway for the server and has IP address Bond1 has three subinterfaces with VLAN 4, 36, 41. IP addresses are,, respectively. Proper communication with other servers on the network we should use routing tables. There are three

PowerShell Script for Switching Between Multiple Windows

Windows PowerShell has strong capabilities. I have a separate computer with a big lcd screen in which I am watching regularly some web based monitoring applications. So I need those application windows switch between on a timely basis. Then I wrote this simple powershell script to achieve this. You can change it according to your needs.