/usr/bin/bash: Difference between revisions

Unless otherwise noted, each builtin command documented in this section as accepting options preceded by - accepts -- to signify the end of the options.  The :, true, false, and test/[ builtins do not accept options and do not treat -- specially.  The exit, logout, return, break,  continue, let,  and  shift  builtins  accept  and  process arguments beginning with - without requiring --.

Other builtins that accept arguments but are not specified as accepting options  interpret  arguments beginning with - as invalid options and require -- to prevent this interpretation.

;<nowiki>: [arguments]</nowiki>

:No  effect;  the command does nothing beyond expanding arguments and performing any specified redirections.  The return status is zero.

;<nowiki>.  filename [arguments]</nowiki>

;<nowiki>source filename [arguments]</nowiki>

:Read and execute commands from filename in the current shell environment  and  return  the exit  status  of  the last command executed from filename.  If filename does not contain a slash, filenames in PATH are used to find the directory  containing  filename.  The  file searched  for in PATH need not be executable.  When bash is not in posix mode, the current directory is searched if no file is found in PATH.  If the sourcepath option to the  shopt builtin  command  is turned off, the PATH is not searched.  If any arguments are supplied, they become the positional parameters when filename is executed.  Otherwise the positional parameters are unchanged.  If the -T option is enabled, source inherits any trap on DEBUG; if it is not, any DEBUG trap string is saved and restored around the call to  source,  and source  unsets  the  DEBUG trap while it executes.  If -T is not set, and the sourced file changes the DEBUG trap, the new value is retained when source completes.  The return  status is the status of the last command exited within the script (0 if no commands are executed), and false if filename is not found or cannot be read.

;<nowiki>alias [-p] [name[=value] ...]</nowiki>

: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.

;<nowiki>bg [jobspec ...]</nowiki>

: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.

;<nowiki>bind [-m keymap] [-lpsvPSVX]</nowiki>

;<nowiki>bind [-m keymap] [-q function] [-u function] [-r keyseq]</nowiki>

;<nowiki>bind [-m keymap] -f filename</nowiki>

;<nowiki>bind [-m keymap] -x keyseq:shell-command</nowiki>

;<nowiki>bind [-m keymap] keyseq:function-name</nowiki>

;<nowiki>bind [-m keymap] keyseq:readline-command</nowiki>

:Display current readline key and function bindings, bind a  key  sequence  to  a  readline function  or  macro, or set a readline variable.  Each non-option argument is a command as it would appear in .inputrc, but each binding or command must be passed as a separate  argument;  e.g.,  '"\C-x\C-r": re-read-init-file'.  Options, if supplied, have the following meanings:

::;-m keymap

:::Use keymap as the keymap to be affected by  the  subsequent  bindings.  Acceptable keymap  names  are  emacs,  emacs-standard,  emacs-meta,  emacs-ctlx,  vi, vi-move, vi-command, and vi-insert.  vi is equivalent to vi-command (vi-move is also a  synonym); emacs is equivalent to emacs-standard.

::;-l

:::List the names of all readline functions.

::;-p

:::Display  readline  function  names  and bindings in such a way that they can be re-read.

::;-P

:::List current readline function names and bindings.

::;-s

:::Display readline key sequences bound to macros and the strings they output in  such a way that they can be re-read.

::;-S

:::Display readline key sequences bound to macros and the strings they output.

::;-v

:::Display readline variable names and values in such a way that they can be re-read.

::;-V

:::List current readline variable names and values.

::;-f filename

:::Read key bindings from filename.

::;-q function

:::Query about which keys invoke the named function.

::;-u function

:::Unbind all keys bound to the named function.

::;-r keyseq

:::Remove any current binding for keyseq.

::;-x keyseq:shell-command

:::Cause  shell-command to be executed whenever keyseq is entered.  When shell-command is executed, the shell sets the READLINE_LINE variable to the contents of the read‐line line buffer and the READLINE_POINT and READLINE_MARK variables to the current location of the insertion point and the saved insertion point (the  mark),  respectively.  If  the executed command changes the value of any of READLINE_LINE, READLINE_POINT, or READLINE_MARK, those new values will be reflected  in  the  editing state.

::;-X

:::List  all  key  sequences  bound to shell commands and the associated commands in a format that can be reused as input.

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

;break [n]

:Exit from within a for, while, until, or select loop.  If n is specified, break n  levels. n  must  be  ≥ 1.  If n is greater than the number of enclosing loops, all enclosing loops are exited.  The return value is 0 unless n is not greater than or equal to 1.

;<nowiki>builtin shell-builtin [arguments]</nowiki>

: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.

;<nowiki>caller [expr]</nowiki>

:Returns the context of any active subroutine call (a shell function or a  script  executed with  the . or source builtins).  Without expr, caller displays the line number and source filename of the current subroutine call.  If a non-negative integer is supplied  as  expr, caller  displays  the  line number, subroutine name, and source file corresponding to that position in the current execution call stack.  This extra information may be used, for example,  to  print a stack trace.  The current frame is frame 0.  The return value is 0 unless the shell is not executing a subroutine call or expr does not correspond to  a  valid position in the call stack.

;<nowiki>cd [-L|[-P [-e]] [-@]] [dir]</nowiki>

:Change  the current directory to dir.  if dir is not supplied, the value of the HOME shell variable is the default.  Any additional arguments following dir are ignored.  The  variable CDPATH defines the search path for the directory containing dir: each directory name in CDPATH is searched for dir.  Alternative directory names in CDPATH are separated  by  a colon  (:).  A  null directory name in CDPATH is the same as the current directory, i.e., ``.''.  If dir begins with a slash (/), then CDPATH is not used.  The -P option causes  cd to  use  the physical directory structure by resolving symbolic links while traversing dir and before processing instances of .. in dir (see also the -P option to  the  set  builtin command);  the  -L option forces symbolic links to be followed by resolving the link after processing instances of .. in dir.  If .. appears in dir, it is processed by removing  the immediately previous pathname component from dir, back to a slash or the beginning of dir. If the -e option is supplied with -P, and the current working directory cannot be successfully determined after a successful directory change, cd will return an unsuccessful status.  On systems that support it, the -@ option presents the extended  attributes  associated with a file as a directory.  An argument of - is converted to $OLDPWD before the directory change is attempted.  If a non-empty directory name from CDPATH is used, or  if  - is  the  first  argument, and the directory change is successful, the absolute pathname of the new working directory is written to the standard output.  The return value is true  if the directory was successfully changed; false otherwise.

;<nowiki>command [-pVv] command [arg ...]</nowiki>

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

;<nowiki>compgen [option] [word]</nowiki>

: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.

;<nowiki>complete [-abcdefgjksuv] [-o comp-option] [-DEI] [-A action] [-G globpat] [-W wordlist]</nowiki>

;;<nowiki>[-F function] [-C command] [-X filterpat] [-P prefix] [-S suffix] name [name ...]</nowiki>

;<nowiki>complete -pr [-DEI] [name ...]</nowiki>

Specify  how arguments to each name should be completed.  If the -p option is supplied, or if no options are supplied, existing completion specifications are printed in a  way  that allows  them  to be reused as input.  The -r option removes a completion specification for each name, or, if no names are supplied, all completion specifications.  The -D option indicates that  other  supplied options and actions should apply to the ``default'' command completion; that is, completion attempted on a command for which no completion has  previously been  defined.  The  -E  option  indicates that other supplied options and actions should apply to ``empty'' command completion; that is, completion  attempted  on  a  blank line.  The  -I  option  indicates that other supplied options and actions should apply to completion on the initial non-assignment word on the line, or after  a  command  delimiter such  as  ;  or |, which is usually command name completion.  If multiple options are supplied, the -D option takes precedence over -E, and both take precedence over -I.  If  any of  -D,  -E,  or  -I are supplied, any other name arguments are ignored; these completions only apply to the case specified by the option.

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

Other  options,  if  specified, have the following meanings.  The arguments to the -G, -W, and -X options (and, if necessary, the -P and -S options) should be quoted to protect them from expansion before the complete builtin is invoked.

;;-o comp-option

::The  comp-option  controls  several  aspects of the compspec's behavior beyond the simple generation of completions.  comp-option may be one of:  

:::bashdefault  

::::Perform the rest of the default bash completions if the compspec generates no matches.  

:::default  

::::Use  readline's  default  filename completion if the compspec generates no matches.  

:::dirnames  

::::Perform directory name completion if the compspec generates no matches.

:::filenames

::::Tell readline that the compspec generates filenames, so it can perform any filename-specific  processing  (like  adding  a  slash to directory names, quoting special characters, or suppressing trailing spaces).  Intended  to be used with shell functions.

:::noquote  

::::Tell  readline  not  to  quote  the  completed words if they are filenames (quoting filenames is the default).

:::nosort   

::::Tell readline not to sort the list of possible completions alphabetically.

:::nospace  

::::Tell readline not to append a space (the default) to  words  completed  at the end of the line.

:::plusdirs

::::After  any  matches  defined by the compspec are generated, directory name completion is attempted and any matches are added to the  results  of  the other actions.

;;-A action

::The action may be one of the following to generate a list of possible completions:

:::alias   

::::Alias names.  May also be specified as -a.

:::arrayvar

::::Array variable names.

:::binding  

::::Readline key binding names.

:::builtin  

::::Names of shell builtin commands.  May also be specified as -b.

:::command  

::::Command names.  May also be specified as -c.

:::directory

::::Directory names.  May also be specified as -d.

:::disabled

::::Names of disabled shell builtins.

:::enabled  

::::Names of enabled shell builtins.

:::export   

::::Names of exported shell variables.  May also be specified as -e.

:::file     

::::File names.  May also be specified as -f.

:::function

::::Names of shell functions.

:::group   

::::Group names.  May also be specified as -g.

:::helptopic

::::Help topics as accepted by the help builtin.

:::hostname

::::Hostnames,  as  taken  from the file specified by the HOSTFILE shell variable.

:::job     

::::Job names, if job control is active.  May also be specified as -j.

:::keyword  

::::Shell reserved words.  May also be specified as -k.

:::running  

::::Names of running jobs, if job control is active.

:::service  

::::Service names.  May also be specified as -s.

:::setopt   

::::Valid arguments for the -o option to the set builtin.

:::shopt   

::::Shell option names as accepted by the shopt builtin.

:::signal   

::::Signal names.

:::stopped  

::::Names of stopped jobs, if job control is active.

:::user     

::::User names.  May also be specified as -u.

:::variable

::::Names of all shell variables.  May also be specified as -v.

;;-C command

::command is executed in a subshell environment, and its output is used as the  possible completions.

;;-F function

::The  shell  function  function is executed in the current shell environment.  When the function is executed, the first argument ($1) is the name of the command whose arguments  are  being  completed,  the second argument ($2) is the word being completed, and the third argument ($3) is the word preceding the word being completed on  the  current command line.  When it finishes, the possible completions are retrieved from the value of the COMPREPLY array variable.

;;-G globpat

::The pathname expansion pattern globpat is expanded to generate the  possible  completions.

;;-P prefix

::prefix  is  added at the beginning of each possible completion after all other options have been applied.

;;-S suffix

::suffix is appended to each possible completion after all other options  have  been applied.

;;-W wordlist

::The  wordlist  is split using the characters in the IFS special variable as delimiters, and each resultant word is  expanded.  Shell  quoting  is  honored  within wordlist, in order to provide a mechanism for the words to contain shell metacharacters or characters in the value of IFS.  The possible completions are  the  members of the resultant list which match the word being completed.

;;-X filterpat

::filterpat  is a pattern as used for pathname expansion.  It is applied to the list of possible completions generated by the preceding options and arguments, and each completion  matching filterpat is removed from the list.  A leading ! in filterpat negates the pattern; in this case, any completion not matching  filterpat  is  removed.

:The  return value is true unless an invalid option is supplied, an option other than -p or -r is supplied without a name argument, an attempt is made to remove a completion specification for  a name for which no specification exists, or an error occurs adding a completion specification.

;<nowiki>compopt [-o option] [-DEI] [+o option] [name]</nowiki>

:Modify completion options for each name according to the options, or for the currently-executing completion if no names are supplied.  If no options are given, display the completion options for each name or the current completion.  The possible values of  option  are those  valid for the complete builtin described above.  The -D option indicates that other supplied options should apply to the ``default'' command completion; that  is,  completion attempted on a command for which no completion has previously been defined.  The -E option indicates that other supplied options should apply to ``empty'' command  completion;  that is, completion attempted on a blank line.  The -I option indicates that other supplied options should apply to completion on the initial non-assignment word on the line, or  after a command delimiter such as ; or |, which is usually command name completion.

:The  return value is true unless an invalid option is supplied, an attempt is made to modify the options for a name for which no completion specification exists, or an output  error occurs.

;<nowiki>continue [n]</nowiki>

:Resume  the  next  iteration  of the enclosing for, while, until, or select loop.  If n is specified, resume at the nth enclosing loop.  n must be ≥ 1.  If n  is  greater  than  the number  of  enclosing  loops, the last enclosing loop (the ``top-level'' loop) is resumed. The return value is 0 unless n is not greater than or equal to 1.

;<nowiki>declare [-aAfFgiIlnrtux] [-p] [name[=value] ...]</nowiki>

;<nowiki>typeset [-aAfFgiIlnrtux] [-p] [name[=value] ...]</nowiki>

Declare variables and/or give them attributes.  If no names are  given  then  display  the values  of  variables.  The -p option will display the attributes and values of each name. When -p is used with name arguments, additional options, other than -f  and  -F,  are  ignored.  When  -p  is  supplied without name arguments, it will display the attributes and values of all variables having the attributes specified by the additional options.  If  no other  options are supplied with -p, declare will display the attributes and values of all shell variables.  The -f option will restrict the display to shell functions.  The -F  option inhibits  the display of function definitions; only the function name and attributes are printed.  If the extdebug shell option is enabled using shopt, the  source  file  name and  line  number where each name is defined are displayed as well.  The -F option implies -f.  The -g option forces variables to be created or modified at the  global  scope,  even when  declare  is executed in a shell function.  It is ignored in all other cases.  The -I option causes local variables to inherit the attributes (except the nameref attribute) and value  of any existing variable with the same name at a surrounding scope.  If there is no existing variable, the local variable is initially unset.  The following  options  can  be used to restrict output to variables with the specified attribute or to give variables attributes:

;;-a     

:::Each name is an indexed array variable (see Arrays above).

;;-A

::Each name is an associative array variable (see Arrays above).

;;-f

::Use function names only.

;;-i

::The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC EVALUATION above) is performed when the variable is assigned a value.

;;-l

::When  the  variable is assigned a value, all upper-case characters are converted to lower-case.  The upper-case attribute is disabled.

;;-n

::Give each name the nameref attribute, making it a name reference to  another  variable.  That  other  variable is defined by the value of name.  All references, assignments, and attribute modifications to name, except those using or changing  the -n attribute itself, are performed on the variable referenced by name's value.  The nameref attribute cannot be applied to array variables.

;;-r

::Make names readonly.  These names cannot then be assigned values by subsequent  assignment statements or unset.

;;-t

::Give  each name the trace attribute.  Traced functions inherit the DEBUG and RETURN traps from the calling shell.  The trace attribute has no special meaning for variables.

;;-u

::When  the  variable is assigned a value, all lower-case characters are converted to upper-case.  The lower-case attribute is disabled.

;;-x

::Mark names for export to subsequent commands via the environment.

:Using `+' instead of `-' turns off the attribute instead, with the exceptions that +a  and +A  may  not be used to destroy array variables and +r will not remove the readonly attribute.  When used in a function, declare and typeset make each name local, as with the  local command, unless the -g option is supplied.  If a variable name is followed by =value, the value of the variable is set to value.  When using -a or -A and the  compound  assignment syntax to create array variables, additional attributes do not take effect until subsequent assignments.  The return value is 0 unless an invalid option  is  encountered,  an attempt  is made to define a function using ``-f foo=bar'', an attempt is made to assign a value to a readonly variable, an attempt is made to assign a value to  an  array  variable without using the compound assignment syntax (see Arrays above), one of the names is not a valid shell variable name, an attempt is made to turn off readonly status for  a  readonly variable, an attempt is made to turn off array status for an array variable, or an attempt is made to display a non-existent function with -f.

;<nowiki>dirs [-clpv] [+n] [-n]</nowiki>

:Without options, displays the list of currently remembered directories.  The default  display is on a single line with directory names separated by spaces.  Directories are added to the list with the pushd command; the popd command removes entries from the  list.  The current directory is always the first directory in the stack.

;;-c

::Clears the directory stack by deleting all of the entries.

;;-l

::Produces a listing using full pathnames; the default listing format uses a tilde to denote the home directory.

;;-p

::Print the directory stack with one entry per line.

;;-v

::Print the directory stack with one entry per line, prefixing each  entry  with  its index in the stack.

;;+n

::Displays  the  nth  entry counting from the left of the list shown by dirs when invoked without options, starting with zero.

;;-n

::Displays the nth entry counting from the right of the list shown by dirs  when  invoked without options, starting with zero.

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

;<nowiki>disown [-ar] [-h] [jobspec ... | pid ... ]</nowiki>

:Without options, remove each jobspec from the table of active jobs.  If  jobspec  is  not present,  and  neither  the -a nor the -r option is supplied, the current job is used.  If the -h option is given, each jobspec is not removed from the table, but is marked so  that SIGHUP  is not sent to the job if the shell receives a SIGHUP.  If no jobspec is supplied, the -a option means to remove or mark all jobs; the -r option without a  jobspec  argument restricts  operation  to  running  jobs.  The return value is 0 unless a jobspec does not specify a valid job.

;<nowiki>echo [-neE] [arg ...]</nowiki>

:Output the args, separated by spaces, followed by a newline.  The return status is  0  unless a  write  error occurs.  If -n is specified, the trailing newline is suppressed.  If the -e option is given, interpretation of the following  backslash-escaped  characters  is enabled.  The  -E  option disables the interpretation of these escape characters, even on systems where they are interpreted by default.  The xpg_echo shell option may be  used  to dynamically  determine  whether  or  not  echo expands these escape characters by default. echo does not interpret -- to mean the end of options.  echo interprets the following  escape sequences:

;;\a

::alert (bell)

;;\b

::backspace

;;\c

::suppress further output

;;\e

;;\E

::an escape character

;;\f

::form feed

;;\n

::new line

;;\r

::carriage return

;;\t

::horizontal tab

;;\v

::vertical tab

;;\\

::backslash

;;\0nnn

::the  eight-bit  character  whose  value is the octal value nnn (zero to three octal digits)

;;\xHH

::the eight-bit character whose value is the hexadecimal value HH  (one  or  two  hex digits)

;;\uHHHH

::the  Unicode  (ISO/IEC  10646)  character whose value is the hexadecimal value HHHH (one to four hex digits)

;;\UHHHHHHHH

::the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHHHHHH (one to eight hex digits)

;<nowiki>enable [-a] [-dnps] [-f filename] [name ...]</nowiki>

: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.

;<nowiki>eval [arg ...]</nowiki>

The args are read and concatenated together into a single command.  This command  is  then read  and executed by the shell, and its exit status is returned as the value of eval.  If there are no args, or only null arguments, eval returns 0.

;exec [-cl] [-a name] [command [arguments]]

:If command is specified, it replaces the shell.  No new process is created.  The arguments become the arguments to command.  If the -l option is supplied, the shell places a dash at the beginning of the zeroth argument passed to command.  This is what login(1) does.  The -c option causes command to be executed with an empty environment.  If -a is supplied, the shell passes name as the zeroth argument to the executed command.  If  command  cannot  be executed  for some reason, a non-interactive shell exits, unless the execfail shell option is enabled.  In that case, it returns failure.  An interactive shell  returns  failure  if the  file cannot be executed.  A subshell exits unconditionally if exec fails.  If command is not specified, any redirections take effect in the current shell, and the return status is 0.  If there is a redirection error, the return status is 1.

;exit [n]

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

;<nowiki>export [-fn] [name[=word]] ...</nowiki>

;export -p

:The supplied names are marked for automatic export to the environment of subsequently executed commands.  If the -f option is given, the names refer to functions.  If no names are given, or if the -p option is supplied, a list of  names  of  all  exported  variables  is printed.  The  -n  option  causes the export property to be removed from each name.  If a variable name is followed by =word, the value of the variable is set to word.  export  returns an exit status of 0 unless an invalid option is encountered, one of the names is not a valid shell variable name, or -f is supplied with a name that is not a function.

;<nowiki>fc [-e ename] [-lnr] [first] [last]</nowiki>

;<nowiki>fc -s [pat=rep] [cmd]</nowiki>

:The first form selects a range of commands from first to last from the  history  list  and displays  or  edits and re-executes them.  First and last may be specified as a string (to locate the last command beginning with that string) or as a number (an index into the history list, where a negative number is used as an offset from the current command number). When listing, a first or last of 0 is equivalent to -1 and -0 is equivalent to the current command  (usually  the fc command); otherwise 0 is equivalent to -1 and -0 is invalid.  If last is not specified, it is set to the current command for listing (so that ``fc -l -10'' prints the last 10 commands) and to first otherwise.  If first is not specified, it is set to the previous command for editing and -16 for listing.

:The -n option suppresses the command numbers when listing.  The -r option reverses the order of the commands.  If the -l option is given, the commands are listed on standard output.  Otherwise, the editor given by ename is invoked on a file containing those commands. If  ename  is not given, the value of the FCEDIT variable is used, and the value of EDITOR if FCEDIT is not set.  If neither variable is set, vi is used.  When editing is  complete, the edited commands are echoed and executed.

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

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

;fg [jobspec]

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

;getopts optstring name [arg ...]

: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  supplied  as arg values, 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.

;<nowiki>hash [-lr] [-p filename] [-dt] [name]</nowiki>

:Each  time hash is invoked, the full pathname of the command name is determined by searching the directories in $PATH and remembered.  Any previously-remembered pathname  is  discarded.  If  the -p option is supplied, no path search is performed, and filename is used as the full filename of the command.  The -r option causes the shell to forget all  remembered locations.  The -d option causes the shell to forget the remembered location of each name.  If the -t option is supplied, the full pathname to which each name  corresponds  is printed.  If multiple name arguments are supplied with -t, the name is printed before the hashed full pathname.  The -l option causes output to be displayed in a format that may be reused  as input.  If no arguments are given, or if only -l is supplied, information about remembered commands is printed.  The return status is true unless a name is not  found  or an invalid option is supplied.

;<nowiki>help [-dms] [pattern]</nowiki>

: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.

;<nowiki>history [n]</nowiki>

;history -c

;history -d offset

;history -d start-end

;<nowiki>history -anrw [filename]</nowiki>

;<nowiki>history -p arg [arg ...]</nowiki>

;<nowiki>history -s arg [arg ...]</nowiki>

:With  no options, display the command history list with line numbers.  Lines listed with a * have been modified.  An argument of n lists only the last n lines.  If the  shell  variable HISTTIMEFORMAT is set and not null, it is used as a format string for strftime(3) to display the time stamp associated with each displayed history entry.  No intervening blank is  printed  between  the  formatted time stamp and the history line.  If filename is supplied, it is used as the name of the history file; if not, the value of HISTFILE is  used. Options, if supplied, have the following meanings:

;;-c

::Clear the history list by deleting all the entries.

;;-d offset

::Delete  the  history entry at position offset.  If offset is negative, it is interpreted as relative to one greater than the last history position, so  negative  indices count back from the end of the history, and an index of -1 refers to the current history -d command.

;;-d start-end

::Delete the history entries between positions start and  end,  inclusive.  Positive and negative values for start and end are interpreted as described above.

;;-a

::Append  the ``new'' history lines to the history file.  These are history lines entered since the beginning of the current bash session, but not already appended  to the history file.

;;-n

::Read the history lines not already read from the history file into the current history list.  These are lines appended to the history file since the beginning of the current bash session.

;;-r

::Read the contents of the history file and append them to the current history list.

;;-w

::Write  the current history list to the history file, overwriting the history file's contents.

;;-p

::Perform history substitution on the following args and display the  result  on  the standard output.  Does not store the results in the history list.  Each arg must be quoted to disable normal history expansion.

;;-s

::Store the args in the history list as a single entry.  The last command in the history list is removed before the args are added.

:If  the  HISTTIMEFORMAT  variable  is set, the time stamp information associated with each history entry is written to the history file, marked with the history  comment  character. When the history file is read, lines beginning with the history comment character followed immediately by a digit are interpreted as timestamps for the following history entry.  The return  value  is 0 unless an invalid option is encountered, an error occurs while reading or writing the history file, an invalid offset is supplied as an argument to  -d,  or  the history expansion supplied as an argument to -p fails.

;<nowiki>jobs [-lnprs] [ jobspec ... ]</nowiki>

;<nowiki>jobs -x command [ args ... ]</nowiki>

:The first form lists the active jobs.  The options have the following meanings:

;;-l

::List process IDs in addition to the normal information.

;;-n

::Display  information  only  about  jobs that have changed status since the user was last notified of their status.

;;-p

::List only the process ID of the job's process group leader.

;;-r

::Display only running jobs.

;;-s

::Display only stopped jobs.

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

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

;<nowiki>kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...</nowiki>

;<nowiki>kill -l|-L [sigspec | exit_status]</nowiki>

:Send  the  signal  named  by  sigspec  or signum to the processes named by pid or jobspec. sigspec is either a case-insensitive signal name such as SIGKILL (with or without the  SIG prefix)  or  a  signal number; signum is a signal number.  If sigspec is not present, then SIGTERM is assumed.  An argument of -l lists the signal names.  If any arguments are  supplied when  -l  is  given,  the  names  of the signals corresponding to the arguments are listed, and the return status is 0.  The exit_status argument to -l is a number specifying either a signal number or the exit status of a process terminated by a signal.  The -L option is equivalent to -l.  kill returns true if at least one signal was successfully sent, or false if an error occurs or an invalid option is encountered.

;<nowiki>let arg [arg ...]</nowiki>

: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.

;<nowiki>local [option] [name[=value] ... | - ]</nowiki>

:For each argument, a local variable named name is created, and assigned value.  The option can  be  any of the options accepted by declare.  When local is used within a function, it causes the variable name to have a visible scope restricted to that function and its children.  If name is -, the set of shell options is made local to the function in which local is invoked: shell options changed using the set builtin inside the function  are  restored to  their  original values when the function returns.  The restore is effected as if a series of set commands were executed to restore the values that were  in  place  before  the function.  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.

;<nowiki>mapfile [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]</nowiki>

;<nowiki>readarray  [-d  delim]  [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]</nowiki>

:Read lines from the standard input into the indexed array variable array, or from file descriptor fd if the -u option is supplied.  The variable MAPFILE is the default array.  Options, if supplied, have the following meanings:

;;-d

::The first character of delim is used to terminate each input line, rather than newline.  If delim is the empty string, mapfile will terminate a line when it reads a NUL character.

;;-n

::Copy at most count lines.  If count is 0, all lines are copied.

;;-O

::Begin assigning to array at index origin.  The default index is 0.

;;-s

::Discard the first count lines read.

;;-t

::Remove a trailing delim (default newline) from each line read.

;;-u

::Read lines from file descriptor fd instead of the standard input.

;;-C

::Evaluate callback each time quantum lines are read.  The -c option specifies  quantum.

;;-c

::Specify the number of lines read between each call to callback.

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

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

:mapfile returns successfully unless an invalid option or option argument is supplied,  array is invalid or unassignable, or if array is not an indexed array.

;<nowiki>popd [-n] [+n] [-n]</nowiki>

: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.

;<nowiki>printf [-v var] format [arguments]</nowiki>

:Write the formatted arguments to the standard output under the control of the format.  The -v  option  causes the output to be assigned to the variable var rather than being printed to the standard output.

:The format is a character string which contains three types of objects: plain  characters, which  are  simply  copied  to standard output, character escape sequences, which are converted and copied to the standard output, and format specifications, each of which  causes printing  of  the  next successive argument.  In addition to the standard printf(1) format specifications, printf interprets the following extensions:

;;%b

::causes printf to expand backslash escape sequences in the corresponding argument in the same way as echo -e.

;;%q

::causes  printf  to output the corresponding argument in a format that can be reused as shell input.

;;%(datefmt)T

::causes printf to output the date-time string resulting from using datefmt as a format string for strftime(3).  The corresponding argument is an integer representing the number of seconds since the epoch.  Two special argument values may be used: -1 represents  the current time, and -2 represents the time the shell was invoked.  If no argument is specified, conversion behaves as if -1 had been given.  This  is  an exception to the usual printf behavior.

:The  %b,  %q,  and  %T directives all use the field width and precision arguments from the format specification and write that many bytes from (or use that wide a field for) the expanded argument, which usually contains more characters than the original.

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.

;<nowiki>pushd [-n] [+n] [-n]</nowikI>

;<nowiki>pushd [-n] [dir]</nowiki>

:Adds a directory to the top of the directory stack, or rotates the stack, making  the  new top  of  the  stack the current working directory.  With no arguments, pushd exchanges the top two directories and returns 0, unless the directory stack  is  empty.  Arguments,  if supplied, have the following meanings:

;;-n

::Suppresses  the  normal  change of directory when rotating or adding directories to the stack, so that only the stack is manipulated.

;;+n

::Rotates the stack so that the nth directory (counting from the  left  of  the  list shown by dirs, starting with zero) is at the top.

;;-n

::Rotates  the  stack  so that the nth directory (counting from the right of the list shown by dirs, starting with zero) is at the top.

;;dir

::Adds dir to the directory stack at the top, making it the new current  working  di‐

rectory as if it had been supplied as the argument to the cd builtin.

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

;<nowiki>pwd [-LP]</nowiki>

: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.

;<nowiki>read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t timeout]  [-u fd] [name ...]</nowiki>

:One  line  is  read from the standard input, or from the file descriptor fd supplied as an argument to the -u option, split into words as described above under Word  Splitting,  and the  first  word is assigned to the first name, the second word to the second name, and so on.  If there are more words than names, the remaining words and their intervening  delimiters are assigned to the last name.  If there are fewer words read from the input stream than names, the remaining names are assigned empty values.  The characters in IFS are used to  split the line into words using the same rules the shell uses for expansion (described above under Word Splitting).  The backslash character (\) may be used to remove  any  special meaning for the next character read and for line continuation.  Options, if supplied, have the following meanings:

;;-a aname

::The words are assigned to sequential indices of the array variable aname,  starting at 0.  aname is unset before any new values are assigned.  Other name arguments are ignored.

;;-d delim

::The first character of delim is used to terminate the input line, rather than  newline.  If delim is the empty string, read will terminate a line when it reads a NUL character.

;;-e     

::If the standard input is coming from a terminal, readline (see READLINE  above)  is used  to  obtain  the line.  Readline uses the current (or default, if line editing was not previously active) editing settings, but uses Readline's  default  filename completion.

;;-i text

::If  readline is being used to read the line, text is placed into the editing buffer before editing begins.

;;-n nchars

::read returns after reading nchars characters rather than  waiting  for  a  complete line  of input, but honors a delimiter if fewer than nchars characters are read before the delimiter.

;;-N nchars

::read returns after reading exactly nchars characters rather than waiting for a complete line of input, unless EOF is encountered or read times out.  Delimiter characters encountered in the input are not treated specially and do not cause read  to return until nchars characters are read.  The result is not split on the characters in IFS; the intent is that the variable is assigned  exactly  the  characters  read (with the exception of backslash; see the -r option below).

;;-p prompt

::Display  prompt on standard error, without a trailing newline, before attempting to read any input.  The prompt is displayed only if input is coming from a terminal.

;;-r

::Backslash does not act as an escape character.  The backslash is considered  to  be part  of the line.  In particular, a backslash-newline pair may not then be used as a line continuation.

;;-s

::Silent mode.  If input is coming from a terminal, characters are not echoed.

;;-t timeout

::Cause read to time out and return failure if a complete line of input (or a  specified number  of  characters) is not read within timeout seconds.  timeout may be a decimal number with a fractional portion following the decimal point.  This  option is  only effective if read is reading input from a terminal, pipe, or other special file; it has no effect when reading from regular files.  If read  times  out,  read saves  any  partial  input read into the specified variable name.  If timeout is 0, read returns immediately, without trying to read any data.  The exit status is 0 if input  is available on the specified file descriptor, non-zero otherwise.  The exit status is greater than 128 if the timeout is exceeded.

;;-u fd   

::Read input from file descriptor fd.

:If no names are supplied, the line read, without the ending delimiter but otherwise unmodified,  is assigned to the variable REPLY.  The exit status is zero, unless end-of-file is encountered, read times out (in which case the status is greater than 128), a variable assignment error  (such as assigning to a readonly variable) occurs, or an invalid file descriptor is supplied as the argument to -u.

;<nowiki>readonly [-aAf] [-p] [name[=word] ...]</nowiki>

: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.

;<nowiki>return [n]</nowiki>

:Causes a function to stop executing and return the value specified by n to its caller.  If n is omitted, the return status is that of the last command executed in the function body. If return is executed by a trap handler, the last command used to determine the status  is the  last  command executed before the trap handler.  If return is executed during a DEBUG trap, the last command used to determine the status is the last command  executed  by  the trap  handler before return was invoked.  If return is used outside a function, but during execution of a script by the .  (source) command, it causes the shell  to  stop  executing that script and return either n or the exit status of the last command executed within the script as the exit status of the script.  If n is supplied, the return value is its  least significant 8 bits.  The return status is non-zero if return is supplied a non-numeric argument, or is used outside a function and not during execution of a script by . or source. Any command associated with the RETURN trap is executed before execution resumes after the function or script.

;<nowiki>set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]</nowiki>

;<nowiki>set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]</nowiki>

:Without options, the name and value of each shell variable are displayed in a format  that can  be  reused  as input for setting or resetting the currently-set variables.  Read-only variables cannot be reset.  In posix mode, only shell variables are listed.  The output is sorted  according  to  the  current locale.  When options are specified, they set or unset shell attributes.  Any arguments remaining after option processing are treated  as  values for the positional parameters and are assigned, in order, to $1, $2, ...  $n.  Options, if specified, have the following meanings:

;;-a

::Each variable or function that is created or modified is given the  export  attribute and marked for export to the environment of subsequent commands.

;;-b

::Report  the  status  of terminated background jobs immediately, rather than before the next primary prompt.  This is effective only when job control is enabled.

;;-e

::Exit immediately if a pipeline (which may consist of a single simple  command),  a list,  or a compound command (see SHELL GRAMMAR above), exits with a non-zero status.  The shell does not exit if the command that fails is  part  of  the  command list  immediately  following  a while or until keyword, part of the test following the if or elif reserved words, part of any command executed in a && or || list except the  command following the final && or ||, any command in a pipeline but the last, or if the command's return value is being inverted with !.  If  a  compound command  other  than a subshell returns a non-zero status because a command failed while -e was being ignored, the shell does not exit.  A trap on ERR,  if  set,  is executed before the shell exits.  This option applies to the shell environment and each subshell environment separately (see COMMAND  EXECUTION  ENVIRONMENT  above), and may cause subshells to exit before executing all the commands in the subshell.

::If  a  compound  command or shell function executes in a context where -e is being ignored, none of the commands executed within the  compound  command  or  function body will be affected by the -e setting, even if -e is set and a command returns a failure status.  If a compound command or shell function sets -e  while  executing in  a context where -e is ignored, that setting will not have any effect until the compound command or the command containing the function call completes.

;;-f

::Disable pathname expansion.

;;-h

::Remember the location of commands as they are looked up for  execution.  This  is enabled by default.

;;-k

::All  arguments  in the form of assignment statements are placed in the environment for a command, not just those that precede the command name.

;;-m

::Monitor mode.  Job control is enabled.  This option is on by default for  interactive shells on systems that support it (see JOB CONTROL above).  All processes run in a separate process group.  When a background job completes, the shell prints  a line containing its exit status.

;;-n

::Read  commands  but do not execute them.  This may be used to check a shell script for syntax errors.  This is ignored by interactive shells.

;;-o option-name

::The option-name can be one of the following:

::allexport

:::Same as -a.

::braceexpand

:::Same as -B.

::emacs

:::Use an emacs-style command line editing interface.  This is enabled by de‐

::fault   

:::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 (right‐most) command to exit with a non-zero status, or zero if all  commands  in the pipeline exit successfully.  This option is disabled by default.

::posix

:::Change  the  behavior of bash where the default operation differs from the POSIX standard to match the standard (posix mode).  See SEE ALSO below for a  reference  to a document that details how posix mode affects bash's behavior.

::privileged

:::Same as -p.

::verbose  

:::Same as -v.

::vi

:::Use a vi-style command line editing  interface.  This  also  affects  the editing interface used for read -e.

::xtrace   

:::Same as -x.

::If  -o  is  supplied  with  no  option-name, the values of the current options are printed.  If +o is supplied with no option-name,  a  series  of  set  commands  to recreate the current option settings is displayed on the standard output.

;;-p

::Turn  on privileged mode.  In this mode, the $ENV and $BASH_ENV files are not processed, shell functions are not inherited from the environment, and the SHELLOPTS, BASHOPTS, CDPATH, and GLOBIGNORE variables, if they appear in the environment, are ignored.  If the shell is started with the effective user (group) id not equal  to the  real  user  (group)  id, and the -p option is not supplied, these actions are taken and the effective user id is set to the real user id.  If the -p  option  is supplied  at startup, the effective user id is not reset.  Turning this option off causes the effective user and group ids to be set to the real user and group ids.

;;-t

::Exit after reading and executing one command.

;;-u

::Treat unset variables and parameters other than the special parameters "@" and "*" as  an error when performing parameter expansion.  If expansion is attempted on an unset variable or parameter, the shell prints an error message, and, if not interactive, exits with a non-zero status.

;;-v

::Print shell input lines as they are read.

;;-x

::After expanding each simple command, for command, case command, select command, or arithmetic for command, display the expanded value of PS4, followed by the command and its expanded arguments or associated word list.

;;-B

::The shell performs brace expansion (see Brace Expansion above).  This is on by default.

;;-C

::If set, bash does not overwrite an existing file with the >, >&, and <>  redirection operators.  This may be overridden when creating output files by using the redirection operator >| instead of >.

;;-E

::If set, any trap on ERR is inherited by shell  functions,  command  substitutions, and commands executed in a subshell environment.  The ERR trap is normally not inherited in such cases.

;;-H

::Enable !  style history substitution.  This option is on by default when the shell is interactive.

;;-P

::If  set, the shell does not resolve symbolic links when executing commands such as cd that change the current working directory.  It  uses  the  physical  directory structure instead.  By default, bash follows the logical chain of directories when performing commands which change the current directory.

;;-T

::If set, any traps on DEBUG and RETURN are inherited by  shell  functions,  command substitutions, and commands executed in a subshell environment.  The DEBUG and RETURN traps are normally not inherited in such cases.

;;--

::If no arguments follow this option, then  the  positional  parameters  are  unset.Otherwise, the positional parameters are set to the args, even if some of them begin with a -.

;;-

::Signal the end of options, cause all remaining args to be assigned  to  the  positional parameters.  The -x and -v options are turned off.  If there are no args, the positional parameters remain unchanged.