ings to be displayed or modified with the bind builtin command. The editing mode may be switched during interactive use by using the -o option to the set builtin command (see SHELL BUILTIN COMMANDS below). Readline Variables Readline has variables that can be used to further customize its behav‐ ior. A variable may be set in the inputrc file with a statement of the form set variable-name value Except where noted, readline variables can take the values On or Off (without regard to case). Unrecognized variable names are ignored. When a variable value is read, empty or null values, "on" (case-insensitive), and "1" are equivalent to On. All other values are equivalent to Off. The variables and their default values are: bell-style (audible) Controls what happens when readline wants to ring the terminal bell. If set to none, readline never rings the bell. If set to visible, readline uses a visible bell if one is available. If set to audible, readline attempts to ring the terminal's bell. bind-tty-special-chars (On) If set to On, readline attempts to bind the control characters treated specially by the kernel's terminal driver to their read‐ line equivalents. comment-begin (``#'') The string that is inserted when the readline insert-comment com‐ mand is executed. This command is bound to M-# in emacs mode and to # in vi command mode. completion-ignore-case (Off) If set to On, readline performs filename matching and completion in a case-insensitive fashion. completion-prefix-display-length (0) The length in characters of the common prefix of a list of possi‐ ble completions that is displayed without modification. When set to a value greater than zero, common prefixes longer than this value are replaced with an ellipsis when displaying possible com‐ pletions. completion-query-items (100) This determines when the user is queried about viewing the number of possible completions generated by the possible-completions com‐ mand. It may be set to any integer value greater than or equal to zero. If the number of possible completions is greater than or equal to the value of this variable, the user is asked whether or not he wishes to view them; otherwise they are simply listed on the terminal. convert-meta (On) If set to On, readline will convert characters with the eighth bit set to an ASCII key sequence by stripping the eighth bit and pre‐ fixing an escape character (in effect, using escape as the meta prefix). disable-completion (Off) If set to On, readline will inhibit word completion. Completion characters will be inserted into the line as if they had been mapped to self-insert. editing-mode (emacs) Controls whether readline begins with a set of key bindings simi‐ lar to Emacs or vi. editing-mode can be set to either emacs or vi. echo-control-characters (On) When set to On, on operating systems that indicate they support it, readline echoes a character corresponding to a signal gener‐ ated from the keyboard. enable-keypad (Off) When set to On, readline will try to enable the application keypad when it is called. Some systems need this to enable the arrow keys. enable-meta-key (On) When set to On, readline will try to enable any meta modifier key the terminal claims to support when it is called. On many termi‐ nals, the meta key is used to send eight-bit characters. expand-tilde (Off) If set to On, tilde expansion is performed when readline attempts word completion. history-preserve-point (Off) If set to On, the history code attempts to place point at the same location on each history line retrieved with previous-history or next-history. history-size (0) Set the maximum number of history entries saved in the history list. If set to zero, the number of entries in the history list is not limited. horizontal-scroll-mode (Off) When set to On, makes readline use a single line for display, scrolling the input horizontally on a single screen line when it becomes longer than the screen width rather than wrapping to a new line. input-meta (Off) If set to On, readline will enable eight-bit input (that is, it will not strip the high bit from the characters it reads), regard‐ less of what the terminal claims it can support. The name meta-flag is a synonym for this variable. isearch-terminators (``C-[C-J'') The string of characters that should terminate an incremental search without subsequently executing the character as a command. If this variable has not been given a value, the characters ESC and C-J will terminate an incremental search. keymap (emacs) Set the current readline keymap. The set of valid keymap names is emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-command, and vi-insert. vi is equivalent to vi-command; emacs is equivalent to emacs-standard. The default value is emacs; the value of edit‐ ing-mode also affects the default keymap. mark-directories (On) If set to On, completed directory names have a slash appended. mark-modified-lines (Off) If set to On, history lines that have been modified are displayed with a preceding asterisk (*). mark-symlinked-directories (Off) If set to On, completed names which are symbolic links to directo‐ ries have a slash appended (subject to the value of mark-directo‐ ries). match-hidden-files (On) This variable, when set to On, causes readline to match files whose names begin with a `.' (hidden files) when performing file‐ name completion. If set to Off, the leading `.' must be supplied by the user in the filename to be completed. menu-complete-display-prefix (Off) If set to On, menu completion displays the common prefix of the list of possible completions (which may be empty) before cycling through the list. output-meta (Off) If set to On, readline will display characters with the eighth bit set directly rather than as a meta-prefixed escape sequence. page-completions (On) If set to On, readline uses an internal more-like pager to display a screenful of possible completions at a time. print-completions-horizontally (Off) If set to On, readline will display completions with matches sorted horizontally in alphabetical order, rather than down the screen. revert-all-at-newline (Off) If set to On, readline will undo all changes to history lines before returning when accept-line is executed. By default, his‐ tory lines may be modified and retain individual undo lists across calls to readline. show-all-if-ambiguous (Off) This alters the default behavior of the completion functions. If set to On, words which have more than one possible completion cause the matches to be listed immediately instead of ringing the bell. show-all-if-unmodified (Off) This alters the default behavior of the completion functions in a fashion similar to show-all-if-ambiguous. If set to On, words which have more than one possible completion without any possible partial completion (the possible completions don't share a common prefix) cause the matches to be listed immediately instead of ringing the bell. skip-completed-text (Off) If set to On, this alters the default completion behavior when inserting a single match into the line. It's only active when performing completion in the middle of a word. If enabled, read‐ line does not insert characters from the completion that match characters after point in the word being completed, so portions of the word following the cursor are not duplicated. visible-stats (Off) If set to On, a character denoting a file's type as reported by stat(2) is appended to the filename when listing possible comple‐ tions. Readline Conditional Constructs Readline implements a facility similar in spirit to the conditional com‐ pilation features of the C preprocessor which allows key bindings and variable settings to be performed as the result of tests. There are four parser directives used. $if The $if construct allows bindings to be made based on the editing mode, the terminal being used, or the application using readline. The text of the test extends to the end of the line; no characters are required to isolate it. mode The mode= form of the $if directive is used to test whether readline is in emacs or vi mode. This may be used in con‐ junction with the set keymap command, for instance, to set bindings in the emacs-standard and emacs-ctlx keymaps only if readline is starting out in emacs mode. term The term= form may be used to include terminal-specific key bindings, perhaps to bind the key sequences output by the terminal's function keys. The word on the right side of the = is tested against the both full name of the terminal and the portion of the terminal name before the first -. This allows sun to match both sun and sun-cmd, for instance. application The application construct is used to include application- specific settings. Each program using the readline library sets the application name, and an initialization file can test for a particular value. This could be used to bind key sequences to functions useful for a specific program. For instance, the following command adds a key sequence that quotes the current or previous word in bash: $if Bash # Quote the current or previous word "\C-xq": "\eb\"\ef\"" $endif $endif This command, as seen in the previous example, terminates an $if command. $else Commands in this branch of the $if directive are executed if the test fails. $include This directive takes a single filename as an argument and reads commands and bindings from that file. For example, the following directive would read /etc/inputrc: $include /etc/inputrc Searching Readline provides commands for searching through the command history (see HISTORY below) for lines containing a specified string. There are two search modes: incremental and non-incremental. Incremental searches begin before the user has finished typing the search string. As each character of the search string is typed, readline dis‐ plays the next entry from the history matching the string typed so far. An incremental search requires only as many characters as needed to find the desired history entry. The characters present in the value of the isearch-terminators variable are used to terminate an incremental search. If that variable has not been assigned a value the Escape and Control-J characters will terminate an incremental search. Control-G will abort an incremental search and restore the original line. When the search is terminated, the history entry containing the search string becomes the current line. To find other matching entries in the history list, type Control-S or Control-R as appropriate. This will search backward or forward in the history for the next entry matching the search string typed so far. Any other key sequence bound to a readline command will terminate the search and execute that command. For instance, a newline will terminate the search and accept the line, thereby executing the command from the his‐ tory list. Readline remembers the last incremental search string. If two Control-Rs are typed without any intervening characters defining a new search string, any remembered search string is used. Non-incremental searches read the entire search string before starting to search for matching history lines. The search string may be typed by the user or be part of the contents of the current line. Readline Command Names The following is a list of the names of the commands and the default key sequences to which they are bound. Command names without an accompanying key sequence are unbound by default. In the following descriptions, point refers to the current cursor position, and mark refers to a cursor position saved by the set-mark command. The text between the point and mark is referred to as the region. Commands for Moving beginning-of-line (C-a) Move to the start of the current line. end-of-line (C-e) Move to the end of the line. forward-char (C-f) Move forward a character. backward-char (C-b) Move back a character. forward-word (M-f) Move forward to the end of the next word. Words are composed of alphanumeric characters (letters and digits). backward-word (M-b) Move back to the start of the current or previous word. Words are composed of alphanumeric characters (letters and digits). shell-forward-word Move forward to the end of the next word. Words are delimited by non-quoted shell metacharacters. shell-backward-word Move back to the start of the current or previous word. Words are delimited by non-quoted shell metacharacters. clear-screen (C-l) Clear the screen leaving the current line at the top of the screen. With an argument, refresh the current line without clear‐ ing the screen. redraw-current-line Refresh the current line. Commands for Manipulating the History accept-line (Newline, Return) Accept the line regardless of where the cursor is. If this line is non-empty, add it to the history list according to the state of the HISTCONTROL variable. If the line is a modified history line, then restore the history line to its original state. previous-history (C-p) Fetch the previous command from the history list, moving back in the list. next-history (C-n) Fetch the next command from the history list, moving forward in the list. beginning-of-history (M-<) Move to the first line in the history. end-of-history (M->) Move to the end of the input history, i.e., the line currently being entered. reverse-search-history (C-r) Search backward starting at the current line and moving `up' through the history as necessary. This is an incremental search. forward-search-history (C-s) Search forward starting at the current line and moving `down' through the history as necessary. This is an incremental search. non-incremental-reverse-search-history (M-p) Search backward through the history starting at the current line using a non-incremental search for a string supplied by the user. non-incremental-forward-search-history (M-n) Search forward through the history using a non-incremental search for a string supplied by the user. history-search-forward Search forward through the history for the string of characters between the start of the current line and the point. This is a non-incremental search. history-search-backward Search backward through the history for the string of characters between the start of the current line and the point. This is a non-incremental search. yank-nth-arg (M-C-y) Insert the first argument to the previous command (usually the second word on the previous line) at point. With an argument n, insert the nth word from the previous command (the words in the previous command begin with word 0). A negative argument inserts the nth word from the end of the previous command. Once the argu‐ ment n is computed, the argument is extracted as if the "!n" his‐ tory expansion had been specified. yank-last-arg (M-., M-_) Insert the last argument to the previous command (the last word of the previous history entry). With a numeric argument, behave exactly like yank-nth-arg. Successive calls to yank-last-arg move back through the history list, inserting the last word (or the word specified by the argument to the first call) of each line in turn. Any numeric argument supplied to these successive calls determines the direction to move through the history. A negative argument switches the direction through the history (back or for‐ ward). The history expansion facilities are used to extract the last argument, as if the "!$" history expansion had been speci‐ fied. shell-expand-line (M-C-e) Expand the line as the shell does. This performs alias and his‐ tory expansion as well as all of the shell word expansions. See HISTORY EXPANSION below for a description of history expansion. history-expand-line (M-^) Perform history expansion on the current line. See HISTORY EXPAN‐ SION below for a description of history expansion. magic-space Perform history expansion on the current line and insert a space. See HISTORY EXPANSION below for a description of history expan‐ sion. alias-expand-line Perform alias expansion on the current line. See ALIASES above for a description of alias expansion. history-and-alias-expand-line Perform history and alias expansion on the current line. insert-last-argument (M-., M-_) A synonym for yank-last-arg. operate-and-get-next (C-o) Accept the current line for execution and fetch the next line rel‐ ative to the current line from the history for editing. Any argu‐ ment is ignored. edit-and-execute-command (C-xC-e) Invoke an editor on the current command line, and execute the result as shell commands. Bash attempts to invoke $VISUAL, $EDI‐ TOR, and emacs as the editor, in that order. Commands for Changing Text delete-char (C-d) Delete the character at point. If point is at the beginning of the line, there are no characters in the line, and the last char‐ acter typed was not bound to delete-char, then return EOF. backward-delete-char (Rubout) Delete the character behind the cursor. When given a numeric argument, save the deleted text on the kill ring. forward-backward-delete-char Delete the character under the cursor, unless the cursor is at the end of the line, in which case the character behind the cursor is deleted. quoted-insert (C-q, C-v) Add the next character typed to the line verbatim. This is how to insert characters like C-q, for example. tab-insert (C-v TAB) Insert a tab character. self-insert (a, b, A, 1, !, ...) Insert the character typed. transpose-chars (C-t) Drag the character before point forward over the character at point, moving point forward as well. If point is at the end of the line, then this transposes the two characters before point. Negative arguments have no effect. transpose-words (M-t) Drag the word before point past the word after point, moving point over that word as well. If point is at the end of the line, this transposes the last two words on the line. upcase-word (M-u) Uppercase the current (or following) word. With a negative argu‐ ment, uppercase the previous word, but do not move point. downcase-word (M-l) Lowercase the current (or following) word. With a negative argu‐ ment, lowercase the previous word, but do not move point. capitalize-word (M-c) Capitalize the current (or following) word. With a negative argu‐ ment, capitalize the previous word, but do not move point. overwrite-mode Toggle overwrite mode. With an explicit positive numeric argu‐ ment, switches to overwrite mode. With an explicit non-positive numeric argument, switches to insert mode. This command affects only emacs mode; vi mode does overwrite differently. Each call to readline() starts in insert mode. In overwrite mode, characters bound to self-insert replace the text at point rather than pushing the text to the right. Characters bound to backward-delete-char replace the character before point with a space. By default, this command is unbound. Killing and Yanking kill-line (C-k) Kill the text from point to the end of the line. backward-kill-line (C-x Rubout) Kill backward to the beginning of the line. unix-line-discard (C-u) Kill backward from point to the beginning of the line. The killed text is saved on the kill-ring. kill-whole-line Kill all characters on the current line, no matter where point is. kill-word (M-d) Kill from point to the end of the current word, or if between words, to the end of the next word. Word boundaries are the same as those used by forward-word. backward-kill-word (M-Rubout) Kill the word behind point. Word boundaries are the same as those used by backward-word. shell-kill-word (M-d) Kill from point to the end of the current word, or if between words, to the end of the next word. Word boundaries are the same as those used by shell-forward-word. shell-backward-kill-word (M-Rubout) Kill the word behind point. Word boundaries are the same as those used by shell-backward-word. unix-word-rubout (C-w) Kill the word behind point, using white space as a word boundary.    The word bound‐ aries are the same as forward-word. yank (C-y) Yank the top of the kill ring into the buffer at point. yank-pop (M-y) Rotate the kill ring, and yank the new top. Only works following yank or yank-pop. Numeric Arguments digit-argument (M-0, M-1, ..., M--) Add this digit to the argument already accumulating, or start a new argument. M-- starts a negative argument. universal-argument This is another way to specify an argument. If this command is followed by one or more digits, optionally with a leading minus sign, those digits define the argument. If the command is fol‐ lowed by digits, executing universal-argument again ends the numeric argument, but is otherwise ignored. As a special case, if this command is immediately followed by a character that is nei‐ ther a digit or minus sign, the argument count for the next com‐ mand is multiplied by four. The argument count is initially one, so executing this function the first time makes the argument count four, a second time makes the argument count sixteen, and so on. Completing complete (TAB) Attempt to perform completion on the text before point. Bash attempts completion treating the text as a variable (if the text begins with $), username (if the text begins with ~), hostname (if the text begins with @), or command (including aliases and func‐ tions) in turn. If none of these produces a match, filename com‐ pletion is attempted. possible-completions (M-?) List the possible completions of the text before point. insert-completions (M-*) Insert all completions of the text before point that would have been generated by possible-completions. menu-complete Similar to complete, but replaces the word to be completed with a single match from the list of possible completions. Repeated exe‐ cution of menu-complete steps through the list of possible comple‐ tions, inserting each match in turn. At the end of the list of completions, the bell is rung (subject to the setting of bell-style) and the original text is restored. An argument of n moves n positions forward in the list of matches; a negative argu‐ ment may be used to move backward through the list. This command is intended to be bound to TAB, but is unbound by default. menu-complete-backward Identical to menu-complete, but moves backward through the list of possible completions, as if menu-complete had been given a nega‐ tive argument. This command is unbound by default. delete-char-or-list Deletes the character under the cursor if not at the beginning or end of the line (like delete-char). If at the end of the line, behaves identically to possible-completions. This command is unbound by default. complete-filename (M-/) Attempt filename completion on the text before point. possible-filename-completions (C-x /) List the possible completions of the text before point, treating it as a filename. complete-username (M-~) Attempt completion on the text before point, treating it as a username. possible-username-completions (C-x ~) List the possible completions of the text before point, treating it as a username. complete-variable (M-$) Attempt completion on the text before point, treating it as a shell variable. possible-variable-completions (C-x $) List the possible completions of the text before point, treating it as a shell variable. complete-hostname (M-@) Attempt completion on the text before point, treating it as a hostname. possible-hostname-completions (C-x @) List the possible completions of the text before point, treating it as a hostname. complete-command (M-!) Attempt completion on the text before point, treating it as a com‐ mand name. Command completion attempts to match the text against aliases, reserved words, shell functions, shell builtins, and finally executable filenames, in that order. possible-command-completions (C-x !) List the possible completions of the text before point, treating it as a command name. dynamic-complete-history (M-TAB) Attempt completion on the text before point, comparing the text against lines from the history list for possible completion matches. dabbrev-expand Attempt menu completion on the text before point, comparing the text against lines from the history list for possible completion matches. complete-into-braces (M-{) Perform filename completion and insert the list of possible com‐ pletions enclosed within braces so the list is available to the shell (see Brace Expansion above). Keyboard Macros start-kbd-macro (C-x () Begin saving the characters typed into the current keyboard macro. end-kbd-macro (C-x )) Stop saving the characters typed into the current keyboard macro and store the definition. call-last-kbd-macro (C-x e) Re-execute the last keyboard macro defined, by making the charac‐ ters in the macro appear as if typed at the keyboard. Miscellaneous re-read-init-file (C-x C-r) Read in the contents of the inputrc file, and incorporate any bindings or variable assignments found there. abort (C-g) Abort the current editing command and ring the terminal's bell (subject to the setting of bell-style). do-uppercase-version (M-a, M-b, M-x, ...) If the metafied character x is lowercase, run the command that is bound to the corresponding uppercase character. prefix-meta (ESC) Metafy the next character typed. ESC f is equivalent to Meta-f. undo (C-_, C-x C-u) Incremental undo, separately remembered for each line. revert-line (M-r) Undo all changes made to this line. This is like executing the undo command enough times to return the line to its initial state. tilde-expand (M-&) Perform tilde expansion on the current word. set-mark (C-@, M-<space>) Set the mark to the point. If a numeric argument is supplied, the mark is set to that position. exchange-point-and-mark (C-x C-x) Swap the point with the mark. The current cursor position is set to the saved position, and the old cursor position is saved as the mark. character-search (C-]) A character is read and point is moved to the next occurrence of that character. A negative count searches for previous occur‐ rences. character-search-backward (M-C-]) A character is read and point is moved to the previous occurrence of that character. A negative count searches for subsequent occurrences. skip-csi-sequence Read enough characters to consume a multi-key sequence such as those defined for keys like Home and End. Such sequences begin with a Control Sequence Indicator (CSI), usually ESC-[. If this sequence is bound to "\[", keys producing such sequences will have no effect unless explicitly bound to a readline command, instead of inserting stray characters into the editing buffer. This is unbound by default, but usually bound to ESC-[. insert-comment (M-#) Without a numeric argument, the value of the readline com‐ ment-begin variable is inserted at the beginning of the current line. If a numeric argument is supplied, this command acts as a toggle: if the characters at the beginning of the line do not match the value of comment-begin, the value is inserted, otherwise the characters in comment-begin are deleted from the beginning of the line. In either case, the line is accepted as if a newline had been typed. The default value of comment-begin causes this command to make the current line a shell comment. If a numeric argument causes the comment character to be removed, the line will be executed by the shell. glob-complete-word (M-g) The word before point is treated as a pattern for pathname expan‐ sion, with an asterisk implicitly appended. This pattern is used to generate a list of matching file names for possible comple‐ tions. glob-expand-word (C-x *) The word before point is treated as a pattern for pathname expan‐ sion, and the list of matching file names is inserted, replacing the word. If a numeric argument is supplied, an asterisk is appended before pathname expansion. glob-list-expansions (C-x g) The list of expansions that would have been generated by glob-expand-word is displayed, and the line is redrawn. If a numeric argument is supplied, an asterisk is appended before path‐ name expansion. dump-functions Print all of the functions and their key bindings to the readline output stream. If a numeric argument is supplied, the output is formatted in such a way that it can be made part of an inputrc file. dump-variables Print all of the settable readline variables and their values to the readline output stream. If a numeric argument is supplied, the output is formatted in such a way that it can be made part of an inputrc file. dump-macros Print all of the readline key sequences bound to macros and the strings they output. If a numeric argument is supplied, the out‐ put is formatted in such a way that it can be made part of an inputrc file. display-shell-version (C-x C-v) Display version information about the current instance of bash. Programmable Completion When word completion is attempted for an argument to a command for which a completion specification (a compspec) has been defined using the com‐ plete builtin (see SHELL BUILTIN COMMANDS below), the programmable com‐ pletion facilities are invoked. First, the command name is identified. If the command word is the empty string (completion attempted at the beginning of an empty line), any compspec defined with the -E option to complete is used. If a compspec has been defined for that command, the compspec is used to generate the list of possible completions for the word. If the command word is a full pathname, a compspec for the full pathname is searched for first. If no compspec is found for the full pathname, an attempt is made to find a compspec for the portion following the final slash. If those searches do not result in a compspec, any compspec defined with the -D option to com‐ plete is used as the default. Once a compspec has been found, it is used to generate the list of match‐ ing words. If a compspec is not found, the default bash completion as described above under Completing is performed. First, the actions specified by the compspec are used. Only matches which are prefixed by the word being completed are returned. When the -f or -d option is used for filename or directory name completion, the shell variable FIGNORE is used to filter the matches. Any completions specified by a pathname expansion pattern to the -G option are generated next. The words generated by the pattern need not match the word being completed. The GLOBIGNORE shell variable is not used to filter the matches, but the FIGNORE variable is used. Next, the string specified as the argument to the -W option is consid‐ ered. The string is first split using the characters in the IFS special variable as delimiters. Shell quoting is honored. Each word is then expanded using brace expansion, tilde expansion, parameter and variable expansion, command substitution, and arithmetic expansion, as described above under EXPANSION. The results are split using the rules described above under Word Splitting. The results of the expansion are prefix- matched against the word being completed, and the matching words become the possible completions. After these matches have been generated, any shell function or command specified with the -F and -C options is invoked. When the command or function is invoked, the COMP_LINE, COMP_POINT, COMP_KEY, and COMP_TYPE variables are assigned values as described above under Shell Variables. If a shell function is being invoked, the COMP_WORDS and COMP_CWORD vari‐ ables are also set. When the function or command is invoked, the first argument is the name of the command whose arguments are being completed, the second argument is the word being completed, and the third argument is the word preceding the word being completed on the current command line. No filtering of the generated completions against the word being completed is performed; the function or command has complete freedom in generating the matches. Any function specified with -F is invoked first. The function may use any of the shell facilities, including the compgen builtin described below, to generate the matches. It must put the possible completions in the COMPREPLY array variable. Next, any command specified with the -C option is invoked in an environ‐ ment equivalent to command substitution. It should print a list of com‐ pletions, one per line, to the standard output. Backslash may be used to escape a newline, if necessary. After all of the possible completions are generated, any filter specified with the -X option is applied to the list. The filter is a pattern as used for pathname expansion; a & in the pattern is replaced with the text of the word being completed. A literal & may be escaped with a back‐ slash; the backslash is removed before attempting a match. Any comple‐ tion that matches the pattern will be removed from the list. A leading ! negates the pattern; in this case any completion not matching the pattern will be removed. Finally, any prefix and suffix specified with the -P and -S options are added to each member of the completion list, and the result is returned to the readline completion code as the list of possible completions. If the previously-applied actions do not generate any matches, and the -o dirnames option was supplied to complete when the compspec was defined, directory name completion is attempted. If the -o plusdirs option was supplied to complete when the compspec was defined, directory name completion is attempted and any matches are added to the results of the other actions. By default, if a compspec is found, whatever it generates is returned to the completion code as the full set of possible completions. The default bash completions are not attempted, and the readline default of filename completion is disabled. If the -o bashdefault option was supplied to complete when the compspec was defined, the bash default completions are attempted if the compspec generates no matches. If the -o default option was supplied to complete when the compspec was defined, readline's default completion will be performed if the compspec (and, if attempted, the default bash completions) generate no matches. When a compspec indicates that directory name completion is desired, the programmable completion functions force readline to append a slash to completed names which are symbolic links to directories, subject to the value of the mark-directories readline variable, regardless of the set‐ ting of the mark-symlinked-directories readline variable. There is some support for dynamically modifying completions. This is most useful when used in combination with a default completion specified with complete -D. It's possible for shell functions executed as comple‐ tion handlers to indicate that completion should be retried by returning an exit status of 124. If a shell function returns 124, and changes the compspec associated with the command on which completion is being attempted (supplied as the first argument when the function is executed), programmable completion restarts from the beginning, with an attempt to find a new compspec for that command. This allows a set of completions to be built dynamically as completion is attempted, rather than being loaded all at once. For instance, assuming that there is a library of compspecs, each kept in a file corresponding to the name of the command, the following default completion function would load completions dynamically: _completion_loader() { . "/etc/bash_completion.d/$1.sh" >/dev/null 2>&1 && return 124 } complete -D -F _completion_loader HISTORY When the -o history option to the set builtin is enabled, the shell pro‐ vides access to the command history, the list of commands previously typed. The value of the HISTSIZE variable is used as the number of com‐ mands to save in a history list. The text of the last HISTSIZE commands (default 500) is saved. The shell stores each command in the history list prior to parameter and variable expansion (see EXPANSION above) but after history expansion is performed, subject to the values of the shell variables HISTIGNORE and HISTCONTROL. On startup, the history is initialized from the file named by the vari‐ able HISTFILE (default ~/.bash_history). The file named by the value of HISTFILE is truncated, if necessary, to contain no more than the number of lines specified by the value of HISTFILESIZE. When the history file is read, lines beginning with the history comment character followed immediately by a digit are interpreted as timestamps for the preceding history line. These timestamps are optionally displayed depending on the value of the HISTTIMEFORMAT variable. When an interactive shell exits, the last $HISTSIZE lines are copied from the history list to $HISTFILE. If the histappend shell option is enabled (see the description of shopt under SHELL BUILTIN COMMANDS below), the lines are appended to the his‐ tory file, otherwise the history file is overwritten. If HISTFILE is unset, or if the history file is unwritable, the history is not saved. If the HISTTIMEFORMAT variable is set, time stamps are written to the history file, marked with the history comment character, so they may be preserved across shell sessions. This uses the history comment character to distinguish timestamps from other history lines. After saving the history, the history file is truncated to contain no more than HISTFILE‐ SIZE lines. If HISTFILESIZE is not set, no truncation is performed. The builtin command fc (see SHELL BUILTIN COMMANDS below) may be used to list or edit and re-execute a portion of the history list. The history builtin may be used to display or modify the history list and manipulate the history file. When using command-line editing, search commands are available in each editing mode that provide access to the history list. The shell allows control over which commands are saved on the history list. The HISTCONTROL and HISTIGNORE variables may be set to cause the shell to save only a subset of the commands entered. The cmdhist shell option, if enabled, causes the shell to attempt to save each line of a multi-line command in the same history entry, adding semicolons where necessary to preserve syntactic correctness. The lithist shell option causes the shell to save the command with embedded newlines instead of semicolons. See the description of the shopt builtin below under SHELL BUILTIN COMMANDS for information on setting and unsetting shell options. HISTORY EXPANSION The shell supports a history expansion feature that is similar to the history expansion in csh. This section describes what syntax features are available. This feature is enabled by default for interactive shells, and can be disabled using the +H option to the set builtin com‐ mand (see SHELL BUILTIN COMMANDS below). Non-interactive shells do not perform history expansion by default. History expansions introduce words from the history list into the input stream, making it easy to repeat commands, insert the arguments to a pre‐ vious command into the current input line, or fix errors in previous com‐ mands quickly. History expansion is performed immediately after a complete line is read, before the shell breaks it into words. It takes place in two parts. The first is to determine which line from the history list to use during sub‐ stitution. The second is to select portions of that line for inclusion into the current one. The line selected from the history is the event, and the portions of that line that are acted upon are words. Various modifiers are available to manipulate the selected words. The line is broken into words in the same fashion as when reading input, so that sev‐ eral metacharacter-separated words surrounded by quotes are considered one word. History expansions are introduced by the appearance of the history expansion character, which is ! by default. Only backslash (\) and single quotes can quote the history expansion character. Several characters inhibit history expansion if found immediately follow‐ ing the history expansion character, even if it is unquoted: space, tab, newline, carriage return, and =. If the extglob shell option is enabled, ( will also inhibit expansion. Several shell options settable with the shopt builtin may be used to tai‐ lor the behavior of history expansion. If the histverify shell option is enabled (see the description of the shopt builtin below), and readline is being used, history substitutions are not immediately passed to the shell parser. Instead, the expanded line is reloaded into the readline editing buffer for further modification. If readline is being used, and the histreedit shell option is enabled, a failed history substitution will be reloaded into the readline editing buffer for correction. The -p option to the history builtin command may be used to see what a history expan‐ sion will do before using it. The -s option to the history builtin may be used to add commands to the end of the history list without actually executing them, so that they are available for subsequent recall. The shell allows control of the various characters used by the history expansion mechanism (see the description of histchars above under Shell Variables). The shell uses the history comment character to mark history timestamps when writing the history file. Event Designators An event designator is a reference to a command line entry in the history list. Unless the reference is absolute, events are relative to the cur‐ rent position in the history list. ! Start a history substitution, except when followed by a blank, newline, carriage return, = or ( (when the extglob shell option is enabled using the shopt builtin). !n Refer to command line n. !-n Refer to the current command minus n. !! Refer to the previous command. This is a synonym for `!-1'. !string Refer to the most recent command preceding the current position in the history list starting with string. !?string[?] Refer to the most recent command preceding the current postition in the history list containing string. The trailing ? may be omitted if string is followed immediately by a newline. ^string1^string2^ Quick substitution. Repeat the previous command, replacing string1 with string2. Equivalent to ``!!:s/string1/string2/'' (see Modifiers below). !# The entire command line typed so far. Word Designators Word designators are used to select desired words from the event. A : separates the event specification from the word designator. It may be omitted if the word designator begins with a ^, $, *, -, or %. Words are numbered from the beginning of the line, with the first word being denoted by 0 (zero). Words are inserted into the current line separated by single spaces. 0 (zero) The zeroth word. For the shell, this is the command word. n The nth word. ^ The first argument. That is, word 1. $ The last argument. % The word matched by the most recent `?string?' search. x-y A range of words; `-y' abbreviates `0-y'. * All of the words but the zeroth. This is a synonym for `1-$'. It is not an error to use * if there is just one word in the event; the empty string is returned in that case. x* Abbreviates x-$. x- Abbreviates x-$ like x*, but omits the last word. If a word designator is supplied without an event specification, the pre‐ vious command is used as the event. Modifiers After the optional word designator, there may appear a sequence of one or more of the following modifiers, each preceded by a `:'. h Remove a trailing file name component, leaving only the head. t Remove all leading file name components, leaving the tail. r Remove a trailing suffix of the form .xxx, leaving the basename. e Remove all but the trailing suffix. p Print the new command but do not execute it. q Quote the substituted words, escaping further substitutions. x Quote the substituted words as with q, but break into words at blanks and newlines. s/old/new/ Substitute new for the first occurrence of old in the event line. Any delimiter can be used in place of /. The final delimiter is optional if it is the last character of the event line. The delimiter may be quoted in old and new with a single backslash. If & appears in new, it is replaced by old. A single backslash will quote the &. If old is null, it is set to the last old sub‐ stituted, or, if no previous history substitutions took place, the last string in a !?string[?] search. & Repeat the previous substitution. g Cause changes to be applied over the entire event line. This is used in conjunction with `:s' (e.g., `:gs/old/new/') or `:&'. If used with `:s', any delimiter can be used in place of /, and the final delimiter is optional if it is the last character of the event line. An a may be used as a synonym for g. G Apply the following `s' modifier once to each word in the event line. SHELL BUILTIN COMMANDS Unless otherwise noted, each builtin command documented in this section as accepting options preceded by - accepts -- to signify the end of the options. The :, true, false, and test builtins do not accept options and do not treat -- specially. The exit, logout, break, continue, let, and shift builtins accept and process arguments beginning with - without requiring --. Other builtins that accept arguments but are not specified as accepting options interpret arguments beginning with - as invalid options and require -- to prevent this interpretation. : [arguments] No effect; the command does nothing beyond expanding arguments and performing any specified redirections. A zero exit code is returned. . filename [arguments] source filename [arguments] Read and execute commands from filename in the current shell envi‐ ronment and return the exit status of the last command executed from filename. If filename does not contain a slash, file names in PATH are used to find the directory containing filename. The file searched for in PATH need not be executable. When bash is not in posix mode, the current directory is searched if no file is found in PATH. If the sourcepath option to the shopt builtin com‐ mand is turned off, the PATH is not searched. If any arguments are supplied, they become the positional parameters when filename is executed. Otherwise the positional parameters are unchanged. The return status is the status of the last command exited within the script (0 if no commands are executed), and false if filename is not found or cannot be read. alias [-p] [name[=value] ...] Alias with no arguments or with the -p option prints the list of aliases in the form alias name=value on standard output. When arguments are supplied, an alias is defined for each name whose value is given. A trailing space in value causes the next word to be checked for alias substitution when the alias is expanded. For each name in the argument list for which no value is supplied, the name and value of the alias is printed. Alias returns true unless a name is given for which no alias has been defined. bg [jobspec ...] Resume each suspended job jobspec in the background, as if it had been started with &. If jobspec is not present, the shell's notion of the current job is used. bg jobspec returns 0 unless run when job control is disabled or, when run with job control enabled, any specified jobspec was not found or was started with‐ out 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 vari‐ able. 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 sup‐ plied, 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 equiv‐ alent to emacs-standard. -l List the names of all readline functions. -p Display readline function names and bindings in such a way that they can be re-read. -P List current readline function names and bindings. -s Display readline key sequences bound to macros and the strings they output in such a way that they can be re-read. -S Display readline key sequences bound to macros and the strings they output. -v Display readline variable names and values in such a way that they can be re-read. -V List current readline variable names and values. -f filename Read key bindings from filename. -q function Query about which keys invoke the named function. -u function Unbind all keys bound to the named function. -r keyseq Remove any current binding for keyseq. -x keyseq:shell-command Cause shell-command to be executed whenever keyseq is entered. When shell-command is executed, the shell sets the READLINE_LINE variable to the contents of the readline line buffer and the READLINE_POINT variable to the current location of the insertion point. If the executed command changes the value of READLINE_LINE or READLINE_POINT, those new values will be reflected in the editing state. The return value is 0 unless an unrecognized option is given or an error occurred. break [n] Exit from within a for, while, until, or select loop. If n is specified, break n levels. n must be ≥ 1. If n is greater than the number of enclosing loops, all enclosing loops are exited. The return value is 0 unless n is not greater than or equal to 1. 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 function‐ ality of the builtin within the function. The cd builtin is com‐ monly redefined this way. The return status is false if shell-builtin is not a shell builtin command. caller [expr] Returns the context of any active subroutine call (a shell func‐ tion 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. cd [-L|[-P [-e]]] [dir] Change the current directory to dir. The variable HOME is the default dir. The variable CDPATH defines the search path for the directory containing dir. Alternative directory names in CDPATH are separated by a colon (:). A null directory name in CDPATH is the same as the current directory, i.e., ``.''. If dir begins with a slash (/), then CDPATH is not used. The -P option says to use the physical directory structure instead of following symbolic links (see also the -P option to the set builtin command); the -L option forces symbolic links to be followed. If the -e option is supplied with -P, and the current working directory cannot be suc‐ cessfully determined after a successful directory change, cd will return an unsuccessful status. An argument of - is equivalent to $OLDPWD. If a non-empty directory name from CDPATH is used, or if - is the first argument, and the directory change is successful, the absolute pathname of the new working directory is written to the standard output. The return value is true if the directory was successfully changed; false otherwise. command [-pVv] command [arg ...] Run command with args suppressing the normal shell function lookup. Only builtin commands or commands found in the PATH are executed. If the -p option is given, the search for command is performed using a default value for PATH that is guaranteed to find all of the standard utilities. If either the -V or -v option is supplied, a description of command is printed. The -v option causes a single word indicating the command or file name used to invoke command to be displayed; the -V option produces a more ver‐ bose description. If the -V or -v option is supplied, the exit status is 0 if command was found, and 1 if not. If neither option is supplied and an error occurred or command cannot be found, the exit status is 127. Otherwise, the exit status of the command builtin is the exit status of command. compgen [option] [word] Generate possible completion matches for word according to the options, which may be any option accepted by the complete builtin with the exception of -p and -r, and write the matches to the standard output. When using the -F or -C options, the various shell variables set by the programmable completion facilities, while available, will not have useful values. The matches will be generated in the same way as if the program‐ mable completion code had generated them directly from a comple‐ tion specification with the same flags. If word is specified, only those completions matching word will be displayed. The return value is true unless an invalid option is supplied, or no matches were generated. complete [-abcdefgjksuv] [-o comp-option] [-DE] [-A action] [-G globpat] [-W wordlist] [-F function] [-C command] [-X filterpat] [-P prefix] [-S suffix] name [name ...] complete -pr [-DE] [name ...] Specify how arguments to each name should be completed. If the -p option is supplied, or if no options are supplied, existing com‐ pletion 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 speci‐ fications. The -D option indicates that the remaining options and actions should apply to the ``default'' command completion; that is, completion attempted on a command for which no completion has previously been defined. The -E option indicates that the remain‐ ing options and actions should apply to ``empty'' command comple‐ tion; that is, completion attempted on a blank line. The process of applying these completion specifications when word completion is attempted is described above under Programmable Com‐ pletion. 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 file‐ names, so it can perform any filename-specific processing (like adding a slash to directory names, quoting special characters, or suppressing trailing spaces). Intended to be used with shell functions. nospace Tell readline not to append a space (the default) to words completed at the end of the line. plusdirs After any matches defined by the compspec are gen‐ erated, 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 speci‐ fied as -v. -C command command is executed in a subshell environment, and its output is used as the possible completions. -F function The shell function function is executed in the current shell environment. When it finishes, the possible comple‐ tions are retrieved from the value of the COMPREPLY array variable. -G globpat The pathname expansion pattern globpat is expanded to gen‐ erate the possible completions. -P prefix prefix is added at the beginning of each possible comple‐ tion 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 spe‐ cial variable as delimiters, and each resultant word is expanded. The possible completions are the members of the resultant list which match the word being completed. -X filterpat filterpat is a pattern as used for pathname expansion. It is applied to the list of possible completions generated by the preceding options and arguments, and each comple‐ tion matching filterpat is removed from the list. A lead‐ ing ! in filterpat negates the pattern; in this case, any completion not matching filterpat is removed. The return value is true unless an invalid option is supplied, an option other than -p or -r is supplied without a name argument, an attempt is made to remove a completion specification for a name for which no specification exists, or an error occurs adding a completion specification. compopt [-o option] [-DE] [+o option] [name] Modify completion options for each name according to the options, or for the currently-executing completion if no names are sup‐ plied. If no options are given, display the completion options for each name or the current completion. The possible values of option are those valid for the complete builtin described above. The -D option indicates that the remaining options should apply to the ``default'' command completion; that is, completion attempted on a command for which no completion has previously been defined. The -E option indicates that the remaining options should apply to ``empty'' command completion; that is, completion attempted on a blank line. The return value is true unless an invalid option is supplied, an attempt is made to modify the options for a name for which no com‐ pletion specification exists, or an output error occurs. continue [n] Resume the next iteration of the enclosing for, while, until, or select loop. If n is specified, resume at the nth enclosing loop. n must be ≥ 1. If n is greater than the number of enclosing loops, the last enclosing loop (the ``top-level'' loop) is resumed. The return value is 0 unless n is not greater than or equal to 1. declare [-aAfFgilrtux] [-p] [name[=value] ...] typeset [-aAfFgilrtux] [-p] [name[=value] ...] Declare variables and/or give them attributes. If no names are given then display the values of variables. The -p option will display the attributes and values of each name. When -p is used with name arguments, additional options are ignored. When -p is supplied without name arguments, it will display the attributes and values of all variables having the attributes specified by the additional options. If no other options are supplied with -p, declare will display the attributes and values of all shell vari‐ ables. The -f option will restrict the display to shell func‐ tions. The -F option inhibits the display of function defini‐ tions; only the function name and attributes are printed. If the extdebug shell option is enabled using shopt, the source file name and line number where the function is defined are displayed as well. The -F option implies -f. The -g option forces variables to be created or modified at the global scope, even when declare is executed in a shell function. It is ignored in all other cases. The following options can be used to restrict output to variables with the specified attribute or to give variables attributes: -a Each name is an indexed array variable (see Arrays above). -A Each name is an associative array variable (see Arrays above). -f Use function names only. -i The variable is treated as an integer; arithmetic evalua‐ tion (see ARITHMETIC EVALUATION above) is performed when the variable is assigned a value. -l When the variable is assigned a value, all upper-case char‐ acters are converted to lower-case. The upper-case attribute is disabled. -r Make names readonly. These names cannot then be assigned values by subsequent assignment statements or unset. -t Give each name the trace attribute. Traced functions inherit the DEBUG and RETURN traps from the calling shell. The trace attribute has no special meaning for variables. -u When the variable is assigned a value, all lower-case char‐ acters are converted to upper-case. The lower-case attribute is disabled. -x Mark names for export to subsequent commands via the envi‐ ronment. Using `+' instead of `-' turns off the attribute instead, with the exceptions that +a may not be used to destroy an array variable and +r will not remove the readonly attribute. When used in a function, makes each name local, as with the local command, unless the -g option is supplied, If a variable name is followed by =value, the value of the variable is set to value. The return value is 0 unless an invalid option is encountered, an attempt is made to define a function using ``-f foo=bar'', an attempt is made to assign a value to a readonly variable, an attempt is made to assign a value to an array variable without using the compound assignment syntax (see Arrays above), one of the names is not a valid shell variable name, an attempt is made to turn off readonly status for a readonly variable, an attempt is made to turn off array status for an array variable, or an attempt is made to dis‐ play a non-existent function with -f. dirs [+n] [-n] [-clpv] Without options, displays the list of currently remembered direc‐ tories. The default display is on a single line with directory names separated by spaces. Directories are added to the list with the pushd command; the popd command removes entries from the list. +n Displays the nth entry counting from the left of the list shown by dirs when invoked without options, starting with zero. -n Displays the nth entry counting from the right of the list shown by dirs when invoked without options, starting with zero. -c Clears the directory stack by deleting all of the entries. -l Produces a longer listing; the default listing format uses a tilde to denote the home directory. -p Print the directory stack with one entry per line. -v Print the directory stack with one entry per line, prefix‐ ing each entry with its index in the stack. The return value is 0 unless an invalid option is supplied or n indexes beyond the end of the directory stack. disown [-ar] [-h] [jobspec ...] Without options, each jobspec is removed from the table of active jobs. If jobspec is not present, and neither -a nor -r is sup‐ plied, the shell's notion of the current job is used. If the -h option is given, each jobspec is not removed from the table, but is marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP. If no jobspec is present, and neither the -a nor the -r option is supplied, the current job is used. If no jobspec is supplied, the -a option means to remove or mark all jobs; the -r option without a jobspec argument restricts operation to running jobs. The return value is 0 unless a jobspec does not specify a valid job. echo [-neE] [arg ...] Output the args, separated by spaces, followed by a newline. The return status is always 0. If -n is specified, the trailing new‐ line 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) enable [-a] [-dnps] [-f filename] [name ...] Enable and disable builtin shell commands. Disabling a builtin allows a disk command which has the same name as a shell builtin to be executed without specifying a full pathname, even though the shell normally searches for builtins before disk commands. If -n is used, each name is disabled; otherwise, names are enabled. For example, to use the test binary found via the PATH instead of the shell builtin version, run ``enable -n test''. The -f option means to load the new builtin command name from shared object filename, on systems that support dynamic loading. The -d option will delete a builtin previously loaded with -f. If no name argu‐ ments are given, or if the -p option is supplied, a list of shell builtins is printed. With no other option arguments, the list consists of all enabled shell builtins. If -n is supplied, only disabled builtins are printed. If -a is supplied, the list printed includes all builtins, with an indication of whether or not each is enabled. If -s is supplied, the output is restricted to the POSIX special builtins. The return value is 0 unless a name is not a shell builtin or there is an error loading a new builtin from a shared object. eval [arg ...] The args are read and concatenated together into a single command. This command is then read and executed by the shell, and its exit status is returned as the value of eval. If there are no args, or only null arguments, eval returns 0. exec [-cl] [-a name] [command [arguments]] If command is specified, it replaces the shell. No new process is created. The arguments become the arguments to command. If the -l option is supplied, the shell places a dash at the beginning of the zeroth argument passed to command. This is what login(1) does. The -c option causes command to be executed with an empty environment. If -a is supplied, the shell passes name as the zeroth argument to the executed command. If command cannot be executed for some reason, a non-interactive shell exits, unless the shell option execfail is enabled, in which case it returns failure. An interactive shell returns failure if the file cannot be executed. If command is not specified, any redirections take effect in the current shell, and the return status is 0. If there is a redirection error, the return status is 1. exit [n] Cause the shell to exit with a status of n. If n is omitted, the exit status is that of the last command executed. A trap on EXIT is executed before the shell terminates. export [-fn] [name[=word]] ... export -p The supplied names are marked for automatic export to the environ‐ ment 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 prop‐ erty 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 encoun‐ tered, one of the names is not a valid shell variable name, or -f is supplied with a name that is not a function. fc [-e ename] [-lnr] [first] [last] fc -s [pat=rep] [cmd] Fix Command. In the first form, a range of commands from first to last is selected from the history list. First and last may be specified as a string (to locate the last command beginning with that string) or as a number (an index into the history list, where a negative number is used as an offset from the current command number). If last is not specified it is set to the current com‐ mand for listing (so that ``fc -l -10'' prints the last 10 com‐ mands) 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 com‐ mands. If ename is not given, the value of the FCEDIT variable is used, and the value of EDITOR if FCEDIT is not set. If neither variable is set, vi is used. When editing is complete, the edited commands are echoed and executed. In the second form, command is re-executed after each instance of pat is replaced by rep. A useful alias to use with this is ``r="fc -s"'', so that typing ``r cc'' runs the last command beginning with ``cc'' and typing ``r'' re-executes the last com‐ mand. If the first form is used, the return value is 0 unless an invalid option is encountered or first or last specify history lines out of range. If the -e option is supplied, the return value is the value of the last command executed or failure if an error occurs with the temporary file of commands. If the second form is used, the return status is that of the command re-executed, unless cmd does not specify a valid history line, in which case fc returns failure. fg [jobspec] Resume jobspec in the foreground, and make it the current job. If jobspec is not present, the shell's notion of the current job is used. The return value is that of the command placed into the foreground, or failure if run when job control is disabled or, when run with job control enabled, if jobspec does not specify a valid job or jobspec specifies a job that was started without job control. getopts optstring name [args] getopts is used by shell procedures to parse positional parame‐ ters. optstring contains the option characters to be recognized; if a character is followed by a colon, the option is expected to have an argument, which should be separated from it by white space. The colon and question mark characters may not be used as option characters. Each time it is invoked, getopts places the next option in the shell variable name, initializing name if it does not exist, and the index of the next argument to be processed into the variable OPTIND. OPTIND is initialized to 1 each time the shell or a shell script is invoked. When an option requires an argument, getopts places that argument into the variable OPTARG. The shell does not reset OPTIND automatically; it must be manually reset between multiple calls to getopts within the same shell invocation if a new set of parameters is to be used. When the end of options is encountered, getopts exits with a return value greater than zero. OPTIND is set to the index of the first non-option argument, and name is set to ?. getopts normally parses the positional parameters, but if more arguments are given in args, getopts parses those instead. getopts can report errors in two ways. If the first character of optstring is a colon, silent error reporting is used. In normal operation diagnostic messages are printed when invalid options or missing option arguments are encountered. If the variable OPTERR is set to 0, no error messages will be displayed, even if the first character of optstring is not a colon. If an invalid option is seen, getopts places ? into name and, if not silent, prints an error message and unsets OPTARG. If getopts is silent, the option character found is placed in OPTARG and no diagnostic message is printed. If a required argument is not found, and getopts is not silent, a question mark (?) is placed in name, OPTARG is unset, and a diag‐ nostic message is printed. If getopts is silent, then a colon (:) is placed in name and OPTARG is set to the option character found. getopts returns true if an option, specified or unspecified, is found. It returns false if the end of options is encountered or an error occurs. hash [-lr] [-p filename] [-dt] [name] Each time hash is invoked, the full pathname of the command name is determined by searching the directories in $PATH and remem‐ bered. Any previously-remembered pathname is discarded. If the -p option is supplied, no path search is performed, and filename is used as the full file name of the command. The -r option causes the shell to forget all remembered locations. The -d option causes the shell to forget the remembered location of each name. If the -t option is supplied, the full pathname to which each name corresponds is printed. If multiple name arguments are supplied with -t, the name is printed before the hashed full path‐ name. The -l option causes output to be displayed in a format that may be reused as input. If no arguments are given, or if only -l is supplied, information about remembered commands is printed. The return status is true unless a name is not found or an invalid option is supplied. help [-dms] [pattern] Display helpful information about builtin commands. If pattern is specified, help gives detailed help on all commands matching pat‐ tern; otherwise help for all the builtins and shell control struc‐ tures is printed. -d Display a short description of each pattern -m Display the description of each pattern in a manpage-like format -s Display only a short usage synopsis for each pattern The return status is 0 unless no command matches pattern. history [n] history -c history -d offset history -anrw [filename] history -p arg [arg ...] history -s arg [arg ...] With no options, display the command history list with line num‐ bers. Lines listed with a * have been modified. An argument of n lists only the last n lines. If the shell variable HISTTIMEFORMAT is set and not null, it is used as a format string for strftime(3) to display the time stamp associated with each displayed history entry. No intervening blank is printed between the formatted time stamp and the history line. If filename is supplied, it is used as the name of the history file; if not, the value of HISTFILE is used. Options, if supplied, have the following meanings: -c Clear the history list by deleting all the entries. -d offset Delete the history entry at position offset. -a Append the ``new'' history lines (history lines entered since the beginning of the current bash session) to the history file. -n Read the history lines not already read from the history file into the current history list. These are lines appended to the history file since the beginning of the current bash session. -r Read the contents of the history file and use them as the current history. -w Write the current history to the history file, overwriting the history file's contents. -p Perform history substitution on the following args and dis‐ play 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 fol‐ lowed immediately by a digit are interpreted as timestamps for the previous history line. The return value is 0 unless an invalid option is encountered, an error occurs while reading or writing the history file, an invalid offset is supplied as an argument to -d, or the history expansion supplied as an argument to -p fails. jobs [-lnprs] [ jobspec ... ] jobs -x command [ args ... ] The first form lists the active jobs. The options have the fol‐ lowing meanings: -l List process IDs in addition to the normal information. -n Display information only about jobs that have changed sta‐ tus since the user was last notified of their status. -p List only the process ID of the job's process group leader. -r Restrict output to running jobs. -s Restrict output to stopped jobs. If jobspec is given, output is restricted to information about that job. The return status is 0 unless an invalid option is encountered or an invalid jobspec is supplied. If the -x option is supplied, jobs replaces any jobspec found in command or args with the corresponding process group ID, and exe‐ cutes 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 above). If the last arg evaluates to 0, let returns 1; 0 is returned otherwise. local [option] [name[=value] ...] For each argument, a local variable named name is created, and assigned value. The option can be any of the options accepted by declare. When local is used within a function, it causes the variable name to have a visible scope restricted to that function and its children. With no operands, local writes a list of local variables to the standard output. It is an error to use local when not within a function. The return status is 0 unless local is used outside a function, an invalid name is supplied, or name is a readonly variable. logout Exit a login shell. mapfile [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array] readarray [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array] Read lines from the standard input into the indexed array variable array, or from file descriptor fd if the -u option is supplied. The variable MAPFILE is the default array. Options, if supplied, have the following meanings: -n Copy at most count lines. If count is 0, all lines are copied. -O Begin assigning to array at index origin. The default index is 0. -s Discard the first count lines read. -t Remove a trailing newline from each line read. -u Read lines from file descriptor fd instead of the standard input. -C Evaluate callback each time quantum lines are read. The -c option specifies quantum. -c Specify the number of lines read between each call to call‐ back. If -C is specified without -c, the default quantum is 5000. When callback is evaluated, it is supplied the index of the next array element to be assigned and the line to be assigned to that element as additional arguments. callback is evaluated after the line is read but before the array element is assigned. If not supplied with an explicit origin, mapfile will clear array before assigning to it. mapfile returns successfully unless an invalid option or option argument is supplied, array is invalid or unassignable, or if array is not an indexed array. popd [-n] [+n] [-n] Removes entries from the directory stack. With no arguments, removes the top directory from the stack, and performs a cd to the new top directory. Arguments, if supplied, have the following meanings: -n Suppresses the normal change of directory when removing directories from the stack, so that only the stack is manipulated. +n Removes the nth entry counting from the left of the list shown by dirs, starting with zero. For example: ``popd +0'' removes the first directory, ``popd +1'' the second. -n Removes the nth entry counting from the right of the list shown by dirs, starting with zero. For example: ``popd -0'' removes the last directory, ``popd -1'' the next to last. If the popd command is successful, a dirs is performed as well, and the return status is 0. popd returns false if an invalid option is encountered, the directory stack is empty, a non-exis‐ tent directory stack entry is specified, or the directory change fails. printf [-v var] format [arguments] Write the formatted arguments to the standard output under the control of the format. The -v option causes the output to be assigned to the variable var rather than being printed to the standard output. The format is a character string which contains three types of objects: plain characters, which are simply copied to standard output, character escape sequences, which are converted and copied to the standard output, and format specifications, each of which causes printing of the next successive argument. In addition to the standard printf(1) format specifications, printf interprets the following extensions: %b causes printf to expand backslash escape sequences in the corresponding argument (except that \c terminates output, backslashes in \', \", and \? are not removed, and octal escapes beginning with \0 may contain up to four digits). %q causes printf to output the corresponding argument in a format that can be reused as shell input. %(datefmt)T causes printf to output the date-time string resulting from using datefmt as a format string for strftime(3). The cor‐ responding 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 repre‐ sents the time the shell was invoked. Arguments to non-string format specifiers are treated as C con‐ stants, 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 suc‐ cess, non-zero on failure. pushd [-n] [+n] [-n] pushd [-n] [dir] Adds a directory to the top of the directory stack, or rotates the stack, making the new top of the stack the current working direc‐ tory. With no arguments, exchanges the top two directories and returns 0, unless the directory stack is empty. Arguments, if supplied, have the following meanings: -n Suppresses the normal change of directory when adding directories to the stack, so that only the stack is manipu‐ lated. +n Rotates the stack so that the nth directory (counting from the left of the list shown by dirs, starting with zero) is at the top. -n Rotates the stack so that the nth directory (counting from the right of the list shown by dirs, starting with zero) is at the top. dir Adds dir to the directory stack at the top, making it the new current working directory. If the pushd command is successful, a dirs is performed as well. If the first form is used, pushd returns 0 unless the cd to dir fails. With the second form, pushd returns 0 unless the directory stack is empty, a non-existent directory stack element is speci‐ fied, or the directory change to the specified new current direc‐ tory 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 con‐ tain symbolic links. The return status is 0 unless an error occurs while reading the name of the current directory or an invalid option is supplied. read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t timeout] [-u fd] [name ...] One line is read from the standard input, or from the file descriptor fd supplied as an argument to the -u option, and the first word is assigned to the first name, the second word to the second name, and so on, with leftover words and their intervening separators assigned to the last name. If there are fewer words read from the input stream than names, the remaining names are assigned empty values. The characters in IFS are used to split the line into words. The backslash character (\) may be used to remove any special meaning for the next character read and for line continuation. Options, if supplied, have the following mean‐ ings: -a aname The words are assigned to sequential indices of the array variable aname, starting at 0. aname is unset before any new values are assigned. Other name arguments are ignored. -d delim The first character of delim is used to terminate the input line, rather than newline. -e If the standard input is coming from a terminal, readline (see READLINE above) is used to obtain the line. Readline uses the current (or default, if line editing was not pre‐ viously active) editing settings. -i text If readline is being used to read the line, text is placed into the editing buffer before editing begins. -n nchars read returns after reading nchars characters rather than waiting for a complete line of input, but honor a delimiter if fewer than nchars characters are read before the delim‐ iter. -N nchars read returns after reading exactly nchars characters rather than waiting for a complete line of input, unless EOF is encountered or read times out. Delimiter characters encountered in the input are not treated specially and do not cause read to return until nchars characters are read. -p prompt Display prompt on standard error, without a trailing 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 particular, a backslash-newline pair may not be used as a line continu‐ ation. -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. timeout may be a decimal number with a fractional portion following the decimal point. This option is only effective if read is reading input from a terminal, pipe, or other special file; it has no effect when reading from regular files. If timeout is 0, read returns success if input is available on the specified file descriptor, failure otherwise. The exit status is greater than 128 if the timeout is exceeded. -u fd Read input from file descriptor fd. If no names are supplied, the line read is assigned to the vari‐ able REPLY. The return code is zero, unless end-of-file is encountered, read times out (in which case the return code is greater than 128), or an invalid file descriptor is supplied as the argument to -u. readonly [-aAf] [-p] [name[=word] ...] The given names are marked readonly; the values of these names may not be changed by subsequent assignment. If the -f option is sup‐ plied, 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 vari‐ able name, or -f is supplied with a name that is not a function. return [n] Causes a function to exit with the return value specified by n. If n is omitted, the return status is that of the last command executed in the function body. If used outside a function, but during execution of a script by the . (source) command, it causes the shell to stop executing that script and return either n or the exit status of the last command executed within the script as the exit status of the script. If used outside a function and not during execution of a script by ., the return status is false. Any command associated with the RETURN trap is executed before execution resumes after the function or script. set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...] set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...] Without options, the name and value of each shell variable are displayed in a format that can be reused as input for setting or resetting the currently-set variables. Read-only variables cannot be reset. In posix mode, only shell variables are listed. The output is sorted according to the current locale. When options are specified, they set or unset shell attributes. Any arguments remaining after option processing are treated as values for the positional parameters and are assigned, in order, to $1, $2, ... $n. Options, if specified, have the following meanings: -a Automatically mark variables and functions which are modi‐ fied or created for export to the environment of subse‐ quent 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 pipeline (which may consist of a single simple command), a subshell command enclosed in parentheses, or one of the commands executed as part of a command list enclosed by braces (see SHELL GRAMMAR above) exits with a non-zero status. The shell does not exit if the command that fails is part of the command list immedi‐ ately following a while or until keyword, part of the test following the if or elif reserved words, part of any com‐ mand executed in a && or || list except the command fol‐ lowing the final && or ||, any command in a pipeline but the last, or if the command's return value is being inverted with !. A trap on ERR, if set, is executed before the shell exits. This option applies to the shell environment and each subshell environment separately (see COMMAND EXECUTION ENVIRONMENT above), and may cause sub‐ shells to exit before executing all the commands in the subshell. -f Disable pathname expansion. -h Remember the location of commands as they are looked up for execution. This is enabled by default. -k All arguments in the form of assignment statements are placed in the environment for a command, not just those that precede the command name. -m Monitor mode. Job control is enabled. This option is on by default for interactive shells on systems that support it (see JOB CONTROL above). Background processes run in a separate process group and a line containing their exit status is printed upon their completion. -n Read commands but do not execute them. This may be used to check a shell script for syntax errors. This is ignored by interactive shells. -o option-name The option-name can be one of the following: allexport Same as -a. braceexpand Same as -B. emacs Use an emacs-style command line editing interface. This is enabled by default when the shell is interactive, unless the shell is started with the --noediting option. This also affects the editing interface used for read -e. errexit Same as -e. errtrace Same as -E. functrace Same as -T. hashall Same as -h. histexpand Same as -H. history Enable command history, as described above under HISTORY. This option is on by default in interac‐ tive shells. ignoreeof The effect is as if the shell command ``IGNOREEOF=10'' had been executed (see Shell Variables above). keyword Same as -k. monitor Same as -m. noclobber Same as -C. noexec Same as -n. noglob Same as -f. nolog Currently ignored. notify Same as -b. nounset Same as -u. onecmd Same as -t. physical Same as -P. pipefail If set, the return value of a pipeline is the value of the last (rightmost) command to exit with a non-zero status, or zero if all commands in the pipeline exit successfully. This option is dis‐ abled by default. posix Change the behavior of bash where the default operation differs from the POSIX standard to match the standard (posix mode). privileged Same as -p. verbose Same as -v. vi Use a vi-style command line editing interface. This also affects the editing interface used for read -e. xtrace Same as -x. If -o is supplied with no option-name, the values of the current options are printed. If +o is supplied with no option-name, a series of set commands to recreate the cur‐ rent 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 spe‐ cial 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, 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 overrid‐ den when creating output files by using the redirection operator >| instead of >. -E If set, any trap on ERR is inherited by shell functions, command substitutions, and commands executed in a subshell environment. The ERR trap is normally not inherited in such cases. -H Enable ! style history substitution. This option is on by default when the shell is interactive. -P If set, the shell does not follow symbolic links when exe‐ cuting 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 cur‐ rent directory. -T If set, any traps on DEBUG and RETURN are inherited by shell functions, command substitutions, and commands exe‐ cuted 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 encountered. shift [n] The positional parameters from n+1 ... are renamed to $1 .... Parameters represented by the numbers $# down to $#-n+1 are unset. n must be a non-negative number less than or equal to $#. If n is 0, no parameters are changed. If n is not given, it is assumed to be 1. If n is greater than $#, the positional parameters are not changed. The return status is greater than zero if n is greater than $# or less than zero; otherwise 0. shopt [-pqsu] [-o] [optname ...] Toggle the values of variables controlling optional shell 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 follow‐ ing meanings: -s Enable (set) each optname. -u Disable (unset) each optname. -q Suppresses normal output (quiet mode); the return status indicates whether the optname is set or unset. If multiple optname arguments are given with -q, the return status is zero if all optnames are enabled; non-zero otherwise. -o Restricts the values of optname to be those defined for the -o option to the set builtin. If either -s or -u is used with no optname arguments, the display is limited to those options which are set or unset, respectively. Unless otherwise noted, the shopt options are disabled (unset) by default. The return status when listing options is zero if all optnames are enabled, non-zero otherwise. When setting or unsetting options, the return status is zero unless an optname is not a valid shell option. The list of shopt options is: autocd If set, a command name that is the name of a directory is executed as if it were the argument to the cd command. This option is only used by interactive shells. cdable_vars If set, an argument to the cd builtin command that is not a directory is assumed to be the name of a variable whose value is the directory to change to. cdspell If set, minor errors in the spelling of a directory compo‐ nent 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 command proceeds. This option is only used by interactive shells. checkhash If set, bash checks that a command found in the hash table exists before trying to execute it. If a hashed command no longer exists, a normal path search is performed. checkjobs If set, bash lists the status of any stopped and running jobs before exiting an interactive shell. If any jobs are running, this causes the exit to be deferred until a sec‐ ond exit is attempted without an intervening command (see JOB CONTROL above). The shell always postpones exiting if any jobs are stopped. checkwinsize If set, bash checks the window size after each command and, if necessary, updates the values of LINES and COL‐ UMNS. cmdhist If set, bash attempts to save all lines of a multiple-line command in the same history entry. This allows easy re- editing of multi-line commands. compat31 If set, bash changes its behavior to that of version 3.1 with respect to quoted arguments to the [[ conditional command's =~ operator. compat32 If set, bash changes its behavior to that of version 3.2 with respect to locale-specific string comparison when using the [[ conditional command's < and > operators. Bash versions prior to bash-4.1 use ASCII collation and strcmp(3); bash-4.1 and later use the current locale's collation sequence and strcoll(3). compat40 If set, bash changes its behavior to that of version 4.0 with respect to locale-specific string comparison when using the [[ conditional command's < and > operators (see previous item) and the effect of interrupting a command list. compat41 If set, bash, when in posix mode, treats a single quote in a double-quoted parameter expansion as a special charac‐ ter. The single quotes must match (an even number) and the characters between the single quotes are considered quoted. This is the behavior of posix mode through ver‐ sion 4.1. The default bash behavior remains as in previ‐ ous versions. direxpand If set, bash replaces directory names with the results of word expansion when performing filename completion. This changes the contents of the readline editing buffer. If not set, bash attempts to preserve what the user typed. dirspell If set, bash attempts spelling correction on directory names during word completion if the directory name ini‐ tially supplied does not exist. dotglob If set, bash includes filenames beginning with a `.' in the results of pathname expansion. execfail If set, a non-interactive shell will not exit if it cannot execute the file specified as an argument to the exec builtin command. An interactive shell does not exit if exec fails. expand_aliases If set, aliases are expanded as described above under ALIASES. This option is enabled by default for interac‐ tive shells. extdebug If set, behavior intended for use by debuggers is enabled: 1. The -F option to the declare builtin displays the source file name and line number corresponding to each function name supplied as an argument. 2. If the command run by the DEBUG trap returns a non- zero value, the next command is skipped and not executed. 3. If the command run by the DEBUG trap returns a value of 2, and the shell is executing in a subrou‐ tine (a shell function or a shell script executed by the . or source builtins), a call to return is simulated. 4. BASH_ARGC and BASH_ARGV are updated as described in their descriptions above. 5. Function tracing is enabled: command substitution, shell functions, and subshells invoked with ( com‐ mand ) inherit the DEBUG and RETURN traps. 6. Error tracing is enabled: command substitution, shell functions, and subshells invoked with ( com‐ mand ) inherit the ERR trap. extglob If set, the extended pattern matching features described above under Pathname Expansion are enabled. extquote If set, $'string' and $"string" quoting is performed within ${parameter} expansions enclosed in double quotes. This option is enabled by default. failglob If set, patterns which fail to match filenames during pathname expansion result in an expansion error. force_fignore If set, the suffixes specified by the FIGNORE shell vari‐ able cause words to be ignored when performing word com‐ pletion even if the ignored words are the only possible completions. See SHELL VARIABLES above for a description of FIGNORE. This option is enabled by default. globstar If set, the pattern ** used in a pathname expansion con‐ text will match all files and zero or more directories and subdirectories. If the pattern is followed by a /, only directories and subdirectories match. gnu_errfmt If set, shell error messages are written in the standard GNU error message format. histappend If set, the history list is appended to the file named by the value of the HISTFILE variable when the shell exits, rather than overwriting the file. histreedit If set, and readline is being used, a user is given the opportunity to re-edit a failed history substitution. histverify If set, and readline is being used, the results of history substitution are not immediately passed to the shell parser. Instead, the resulting line is loaded into the readline editing buffer, allowing further modification. hostcomplete If set, and readline is being used, bash will attempt to perform hostname completion when a word containing a @ is being completed (see Completing under READLINE above). This is enabled by default. huponexit If set, bash will send SIGHUP to all jobs when an interac‐ tive login shell exits. interactive_comments If set, allow a word beginning with # to cause that word and all remaining characters on that line to be ignored in an interactive shell (see COMMENTS above). This option is enabled by default. lastpipe If set, and job control is not active, the shell runs the last command of a pipeline not executed in the background in the current shell environment. lithist If set, and the cmdhist option is enabled, multi-line com‐ mands are saved to the history with embedded newlines rather than using semicolon separators where possible. login_shell The shell sets this option if it is started as a login shell (see INVOCATION above). The value may not be changed. mailwarn If set, and a file that bash is checking for mail has been accessed since the last time it was checked, the message ``The mail in mailfile has been read'' is displayed. no_empty_cmd_completion If set, and readline is being used, bash will not attempt to search the PATH for possible completions when comple‐ tion is attempted on an empty line. nocaseglob If set, bash matches filenames in a case-insensitive fash‐ ion when performing pathname expansion (see Pathname Expansion above). nocasematch If set, bash matches patterns in a case-insensitive fash‐ ion when performing matching while executing case or [[ conditional commands. nullglob If set, bash allows patterns which match no files (see Pathname Expansion above) to expand to a null string, rather than themselves. progcomp If set, the programmable completion facilities (see Pro‐ grammable Completion above) are enabled. This option is enabled by default. promptvars 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. restricted_shell The shell sets this option if it is started in restricted mode (see RESTRICTED SHELL below). The value may not be changed. This is not reset when the startup files are executed, allowing the startup files to discover whether or not a shell is restricted. shift_verbose If set, the shift builtin prints an error message when the shift count exceeds the number of positional parameters. sourcepath If set, the source (.) builtin uses the value of PATH to find the directory containing the file supplied as an argument. This option is enabled by default. xpg_echo If set, the echo builtin expands backslash-escape sequences by default. suspend [-f] Suspend the execution of this shell until it receives a SIGCONT signal. A login shell cannot be suspended; the -f option can be used to override this and force the suspension. 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 con‐ ditional expression expr. Each operator and operand must be a separate argument. Expressions are composed of the primaries described above under CONDITIONAL EXPRESSIONS. test does not accept any options, nor does it accept and ignore an argument of -- as signifying the end of options. Expressions may be combined using the following operators, listed in decreasing order of precedence. The evaluation depends on the number of arguments; see below. Operator precedence is used when there are five or more arguments. ! expr True if expr is false. ( expr ) Returns the value of expr. This may be used to override the normal precedence of operators. expr1 -a expr2 True if both expr1 and expr2 are true. expr1 -o expr2 True if either expr1 or expr2 is true. test and [ evaluate conditional expressions using a set of rules based on the number of arguments. 0 arguments The expression is false. 1 argument The expression is true if and only if the argument is not null. 2 arguments If the first argument is !, the expression is true if and only if the second argument is null. If the first argument is one of the unary conditional operators listed above under CONDITIONAL EXPRESSIONS, the expression is true if the unary test is true. If the first argument is not a valid unary conditional operator, the expression is false. 3 arguments The following conditions are applied in the order listed. If the second argument is one of the binary conditional operators listed above under CONDITIONAL EXPRESSIONS, the result of the expression is the result of the binary test using the first and third arguments as operands. The -a and -o operators are considered binary operators when there are three arguments. If the first argument is !, the value is the negation of the two-argument test using the second and third arguments. If the first argument is exactly ( and the third argument is exactly ), the result is the one- argument test of the second argument. Otherwise, the expression is false. 4 arguments If the first argument is !, the result is the negation of the three-argument expression composed of the remaining arguments. Otherwise, the expression is parsed and evalu‐ ated according to precedence using the rules listed above. 5 or more arguments The expression is parsed and evaluated according to prece‐ dence using the rules listed above. When used with test or [, the < and > operators sort lexicographi‐ cally using ASCII ordering. times Print the accumulated user and system times for the shell and for processes run from the shell. The return status is 0. trap [-lp] [[arg] sigspec ...] The command arg is to be read and executed when the shell receives signal(s) sigspec. If arg is absent (and there is a single sigspec) or -, each specified signal is reset to its original dis‐ position (the value it had upon entrance to the shell). If arg is the null string the signal specified by each sigspec is ignored by the shell and by the commands it invokes. If arg is not present and -p has been supplied, then the trap commands associated with each sigspec are displayed. If no arguments are supplied or if only -p is given, trap prints the list of commands associated with each signal. The -l option causes the shell to print a list of signal names and their corresponding numbers. Each sigspec is either a signal name defined in <signal.h>, or a signal number. Signal names are case insensitive and the SIG prefix is optional. If a sigspec is EXIT (0) the command arg is executed on exit from the shell. If a sigspec is DEBUG, the command arg is executed before every simple command, for command, case command, select command, every arithmetic for command, and before the first com‐ mand executes in a shell function (see SHELL GRAMMAR above). Refer to the description of the extdebug option to the shopt builtin for details of its effect on the DEBUG trap. If a sigspec is RETURN, the command arg is executed each time a shell function or a script executed with the . or source builtins finishes exe‐ cuting. If a sigspec is ERR, the command arg is executed whenever a simple command has a non-zero exit status, subject to the following con‐ ditions. The ERR trap is not executed if the failed command is part of the command list immediately following a while or until keyword, part of the test in an if statement, part of a command executed in a && or || list, or if the command's return value is being inverted via !. These are the same conditions obeyed by the errexit option. Signals ignored upon entry to the shell cannot be trapped or reset. Trapped signals that are not being ignored are reset to their original values in a subshell or subshell environment when one is created. The return status is false if any sigspec is invalid; otherwise trap returns true. type [-aftpP] name [name ...] With no options, indicate how each name would be interpreted if used as a command name. If the -t option is used, type prints a string which is one of alias, keyword, function, builtin, or file if name is an alias, shell reserved word, function, builtin, or disk file, respectively. If the name is not found, then nothing is printed, and an exit status of false is returned. If the -p option is used, type either returns the name of the disk file that would be executed if name were specified as a command name, or nothing if ``type -t name'' would not return file. The -P option forces a PATH search for each name, even if ``type -t name'' would not return file. If a command is hashed, -p and -P print the hashed value, not necessarily the file that appears first in PATH. If the -a option is used, type prints all of the places that con‐ tain an executable named name. This includes aliases and func‐ tions, if and only if the -p option is not also used. The table of hashed commands is not consulted when using -a. The -f option suppresses shell function lookup, as with the command builtin. type returns true if all of the arguments are found, false if any are not found. ulimit [-HSTabcdefilmnpqrstuvx [limit]] Provides control over the resources available to the shell and to processes started by it, on systems that allow such control. The -H and -S options specify that the hard or soft limit is set for the given resource. A hard limit cannot be increased by a non- root user once it is set; a soft limit may be increased up to the value of the hard limit. If neither -H nor -S is specified, both the soft and hard limits are set. The value of limit can be a number in the unit specified for the resource or one of the spe‐ cial 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‐ lows: -a All current limits are reported -b The maximum socket buffer size -c The maximum size of core files created -d The maximum size of a process's data segment -e The maximum scheduling priority ("nice") -f The maximum size of files written by the shell and its children -i The maximum number of pending signals -l The maximum size that may be locked into memory -m The maximum resident set size (many systems do not honor this limit) -n The maximum number of open file descriptors (most systems do not allow this value to be set) -p The pipe size in 512-byte blocks (this may not be set) -q The maximum number of bytes in POSIX message queues -r The maximum real-time scheduling priority -s The maximum stack size -t The maximum amount of cpu time in seconds -u The maximum number of processes available to a single user -v The maximum amount of virtual memory available to the shell and, on some systems, to its children -x The maximum number of file locks -T The maximum number of threads If limit is given, it is the new value of the specified resource (the -a option is display only). If no option is given, then -f is assumed. Values are in 1024-byte increments, except for -t, which is in seconds, -p, which is in units of 512-byte blocks, and -T, -b, -n, and -u, which are unscaled values. The return status is 0 unless an invalid option or argument is supplied, or an error occurs while setting a new limit. umask [-p] [-S] [mode] The user file-creation mask is set to mode. If mode begins with a digit, it is interpreted as an octal number; otherwise it is interpreted as a symbolic mode mask similar to that accepted by chmod(1). If mode is omitted, the current value of the mask is printed. The -S option causes the mask to be printed in symbolic form; the default output is an octal number. If the -p option is supplied, and mode is omitted, the output is in a form that may be reused as input. The return status is 0 if the mode was success‐ fully changed or if no mode argument was supplied, and false oth‐ erwise. unalias [-a] [name ...] Remove each name from the list of defined aliases. If -a is sup‐ plied, all alias definitions are removed. The return value is true unless a supplied name is not a defined alias. unset [-fv] [name ...] For each name, remove the corresponding variable or function. If no options are supplied, or the -v option is given, each name refers to a shell variable. Read-only variables may not be unset. If -f is specified, each name refers to a shell function, and the function definition is removed. Each unset variable or function is removed from the environment passed to subsequent commands. If any of COMP_WORDBREAKS, RANDOM, SECONDS, LINENO, HISTCMD, FUNC‐ NAME, GROUPS, or DIRSTACK are unset, they lose their special prop‐ erties, even if they are subsequently reset. The exit status is true unless a name is readonly. wait [n ...] Wait for each specified process and return its termination status. Each n may be a process ID or a job specification; if a job spec is given, all processes in that job's pipeline are waited for. If n is not given, all currently active child processes are waited for, and the return status is zero. If n specifies a non-existent process or job, the return status is 127. Otherwise, the return status is the exit status of the last process or job waited for. RESTRICTED SHELL If bash is started with the name rbash, or the -r option is supplied at invocation, the shell becomes restricted. A restricted shell is used to set up an environment more controlled than the standard shell. It behaves identically to bash with the exception that the following are disallowed or not performed: · changing directories with cd · setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV · specifying command names containing / · specifying a file name containing a / as an argument to the . builtin command · specifying a filename containing a slash as an argument to the -p option to the hash builtin command · importing function definitions from the shell environment at startup · parsing the value of SHELLOPTS from the shell environment at startup · redirecting output using the >, >|, <>, >&, &>, and >> redirection operators · using the exec builtin command to replace the shell with another command · adding or deleting builtin commands with the -f and -d options to the enable builtin command · using the enable builtin command to enable disabled shell builtins · specifying the -p option to the command builtin command · turning off restricted mode with set +r or set +o restricted. These restrictions are enforced after any startup files are read. When a command that is found to be a shell script is executed (see COM‐ MAND EXECUTION above), rbash turns off any restrictions in the shell spawned to execute the script. SEE ALSO Bash Reference Manual, Brian Fox and Chet Ramey The Gnu Readline Library, Brian Fox and Chet Ramey The Gnu History Library, Brian Fox and Chet Ramey Portable Operating System Interface (POSIX) Part 2: Shell and Utilities, IEEE sh(1), ksh(1), csh(1) emacs(1), vi(1) readline(3) FILES /bin/bash The bash executable /etc/profile The systemwide initialization file, executed for login shells /etc/bash.bashrc The systemwide per-interactive-shell startup file /etc/bash.bash.logout The systemwide login shell cleanup file, executed when a login shell exits ~/.bash_profile The personal initialization file, executed for login shells ~/.bashrc The individual per-interactive-shell startup file ~/.bash_logout The individual login shell cleanup file, executed when a login shell exits ~/.inputrc Individual readline initialization file AUTHORS Brian Fox, Free Software Foundation<EMAIL_ADDRESS>Chet Ramey, Case Western Reserve University<EMAIL_ADDRESS>BUG REPORTS If you find a bug in bash, you should report it. But first, you should make sure that it really is a bug, and that it appears in the latest ver‐ sion of bash. The latest version is always available from ftp://ftp.gnu.org/pub/gnu/bash/. Once you have determined that a bug actually exists, use the bashbug com‐ mand to submit a bug report. If you have a fix, you are encouraged to mail that as well! Suggestions and `philosophical' bug reports may be mailed to<EMAIL_ADDRESS>or posted to the Usenet newsgroup gnu.bash.bug. ALL bug reports should include: The version number of bash The hardware and operating system The compiler used to compile A description of the bug behaviour A short script or `recipe' which exercises the bug bashbug inserts the first three items automatically into the template it provides for filing a bug report. Comments and bug reports concerning this manual page should be directed to<EMAIL_ADDRESS>BUGS It's too big and too slow. There are some subtle differences between bash and traditional versions of sh, mostly because of the POSIX specification. Aliases are confusing in some uses. Shell builtin commands and functions are not stoppable/restartable. Compound commands and command sequences of the form `a ; b ; c' are not handled gracefully when process suspension is attempted. When a process is stopped, the shell immediately executes the next command in the sequence. It suffices to place the sequence of commands between paren‐ theses to force it into a subshell, which may be stopped as a unit. Array variables may not (yet) be exported. There may be only one active coprocess at a time. GNU Bash-4.2 2010 December 28 BASH(1)