READLINE

Section: C Library Functions (3)
Updated: 1997 Feb 5
Index Return to Main Contents

NAME

readline - get a line from a user with editing

SYNOPSIS

#include <readline.h>
#include <history.h>

char *readline (prompt)
char *prompt;

COPYRIGHT

DESCRIPTION

readline will read a line from the terminal and return it, using prompt as a prompt. If prompt is null, no prompt is issued. The line returned is allocated with malloc(3), so the caller must free it when finished. The line returned has the final newline removed, so only the text of the line remains.

readline offers editing capabilities while the user is entering the line. By default, the line editing commands are similar to those of emacs. A vi-style line editing interface is also available.

RETURN VALUE

readline returns the text of the line read. A blank line returns the empty string. If EOF is encountered while reading a line, and the line is empty, NULL is returned. If an EOF is read with a non-empty line, it is treated as a newline.

NOTATION

An emacs-style notation is used to denote keystrokes. Control keys are denoted by C-key, e.g., C-n means Control-N. Similarly, meta keys are denoted by M-key, so M-x means Meta-X. (On keyboards without a meta key, M-x means ESC x, i.e., press the Escape key then the x key. This makes ESC the meta prefix. The combination M-C-x means ESC-Control-x, or press the Escape key then hold the Control key while pressing the x key.)

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

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

INITIALIZATION FILE

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

For example, placing

: M-Control-u: universal-argument

: C-Meta-u: universal-argument

into the inputrc would make M-C-u execute the readline command universal-argument.

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

Key Bindings

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

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

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

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

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

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

\C-: control prefix
\M-: meta prefix
\e: an escape character
\\: backslash
\: literal "
\': literal '

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

Bash allows the current readline key bindings to be displayed or modified with the bind builtin command. The editing mode may be switched during interactive use by using the -o option to the set builtin command. Other programs using this library provide similar mechanisms. The inputrc file may be edited and re-read if a program does not provide any other means to incorporate new bindings.

Variables

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

: set variable-name value

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

bell-style (audible): Controls what happens when readline wants to ring the terminal bell. If set to none, readline never rings the bell. If set to visible, readline uses a visible bell if one is available. If set to audible, readline attempts to ring the terminal's bell.
comment-begin (``#''): The string that is inserted in vi mode when the insert-comment command is executed. This command is bound to M-# in emacs mode and to # in vi command mode.
completion-query-items (100): This determines when the user is queried about viewing the number of possible completions generated by the possible-completions command. It may be set to any integer value greater than or equal to zero. If the number of possible completions is greater than or equal to the value of this variable, the user is asked whether or not he wishes to view them; otherwise they are simply listed on the terminal.
convert-meta (On): If set to On, readline will convert characters with the eighth bit set to an ASCII key sequence by stripping the eighth bit and prepending an escape character (in effect, using escape as the meta prefix).
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 similar to emacs or vi. editing-mode can be set to either emacs or vi.
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.
expand-tilde (Off): If set to on, tilde expansion is performed when readline attempts word completion.
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.
keymap (emacs): Set the current readline keymap. The set of legal keymap names is emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command, and vi-insert. vi is equivalent to vi-command; emacs is equivalent to emacs-standard. The default value is emacs; the value of editing-mode also affects the default keymap.
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 (*).
meta-flag (Off): If set to On, readline will enable eight-bit input (that is, it will not strip the high bit from the characters it reads), regardless of what the terminal claims it can support.
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.
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.
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 completions.

Conditional Constructs

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

$if

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

mode

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

term

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

application

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

$if bash
# Quote the current or previous word
"\C-xq": "\eb\"\ef\""
$endif

$endif

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

$else

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

SEARCHING

Readline provides commands for searching through the command history 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 displays 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 Escape character is used to terminate an incremental search. Control-J will also terminate the 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 line 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 history list.

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 part of the contents of the current line.

EDITING COMMANDS

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.

Commands for Moving

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

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. If the line is a modified history line, then restore the history line to its original state.
previous-history (C-p): Fetch the previous command from the history list, moving back in the list.
next-history (C-n): Fetch the next command from the history list, moving forward in the list.
beginning-of-history (M-<): Move to the first line in the history.
end-of-history (M->): Move to the end of the input history, i.e., the line currently being entered.
reverse-search-history (C-r): Search backward starting at the current line and moving `up' through the history as necessary. This is an incremental search.
forward-search-history (C-s): Search forward starting at the current line and moving `down' through the history as necessary. This is an incremental search.
non-incremental-reverse-search-history (M-p): Search backward through the history starting at the current line using a non-incremental search for a string supplied by the user.
non-incremental-forward-search-history (M-n): Search forward through the history using a non-incremental search for a string supplied by the user.
history-search-forward: Search forward through the history for the string of characters between the start of the current line and the current cursor position (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 (the current cursor position). With an argument n, insert the nth word from the previous command (the words in the previous command begin with word 0). A negative argument inserts the nth word from the end of the previous command.
yank-last-arg (M-., M-_): Insert the last argument to the previous command (the last word of the previous history entry). With an argument, behave exactly like yank-nth-arg.

Commands for Changing Text

delete-char (C-d): Delete the character under the cursor. If point is at the beginning of the line, there are no characters in the line, and the last character typed was not C-d, then return EOF.
backward-delete-char (Rubout): Delete the character behind the cursor. When given a numeric argument, save the deleted text on the kill ring.
quoted-insert (C-q, C-v): Add the next character that you type to the line verbatim. This is how to insert characters like C-q, for example.
tab-insert (M-TAB): Insert a tab character.
self-insert (a, b, A, 1, !, ...): Insert the character typed.
transpose-chars (C-t): Drag the character before point forward over the character at point. Point moves forward as well. If point is at the end of the line, then transpose the two characters before point. Negative arguments don't work.
transpose-words (M-t): Drag the word behind the cursor past the word in front of the cursor moving the cursor over that word as well.
upcase-word (M-u): Uppercase the current (or following) word. With a negative argument, do the previous word, but do not move point.
downcase-word (M-l): Lowercase the current (or following) word. With a negative argument, do the previous word, but do not move point.
capitalize-word (M-c): Capitalize the current (or following) word. With a negative argument, do the previous word, but do not move point.

Killing and Yanking

kill-line (C-k): Kill the text from the current cursor position to the end of the line.
backward-kill-line (C-x Rubout): Kill backward to the beginning of the line.
unix-line-discard (C-u): Kill backward from point to the beginning of the line.
kill-whole-line: Kill all characters on the current line, no matter where the cursor is.
kill-word (M-d): Kill from the cursor to the end of the current word, or if between words, to the end of the next word. Word boundaries are the same as those used by forward-word.
backward-kill-word (M-Rubout): Kill the word behind the cursor. Word boundaries are the same as those used by backward-word.
unix-word-rubout (C-w): Kill the word behind the cursor, using white space as a word boundary. The word boundaries are different from backward-kill-word.
delete-horizontal-space (M-\): Delete all spaces and tabs around point.
kill-region: Kill the text between the point and mark (saved cursor position). This text is referred to as the region.
copy-region-as-kill: Copy the text in the region to the kill buffer.
copy-backward-word: Copy the word before point to the kill buffer.
copy-forward-word: Copy the word following point to the kill buffer.
yank (C-y): Yank the top of the kill ring into the buffer at the cursor.
yank-pop (M-y): Rotate the kill ring, and yank the new top. Only works following yank or yank-pop.

Numeric Arguments

digit-argument (M-0, M-1, ..., M--): Add this digit to the argument already accumulating, or start a new argument. M-- starts a negative argument.
universal-argument: 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 followed 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 neither a digit or minus sign, the argument count for the next command 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. The actual completion performed is application-specific. Bash, for instance, attempts completion treating the text as a variable (if the text begins with $), username (if the text begins with ~), hostname (if the text begins with @), or command (including aliases and functions) in turn. If none of these produces a match, filename completion is attempted. Gdb, on the other hand, allows completion of program functions and variables, and only attempts filename completion under certain circumstances.
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.

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 characters in the macro appear as if typed at the keyboard.

Miscellaneous

re-read-init-file (C-x C-r): Read in the contents of 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 typing 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 current 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 occurrences.
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.
insert-comment (M-#): The value of the readline comment-begin variable is inserted at the beginning of the current line, and the line is accepted as if a newline had been typed. This makes the current line a shell comment.
glob-expand-word (C-x *): The word before point is treated as a pattern for pathname expansion, and the list of matching file names is inserted, replacing the word.
glob-list-expansions (C-x g): The list of expansions that would have been generated by glob-expand-word is inserted into the line, replacing the word before point.
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 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 ouput. If a numeric argument is supplied, the output is formatted in such a way that it can be made part of an inputrc file.
emacs-editing-mode (C-e): When in vi editing mode, this causes a switch to emacs editing mode.
vi-editing-mode (M-C-j): When in emacs editing mode, this causes a switch to vi editing mode.

DEFAULT KEY BINDINGS

The following is a list of the default emacs and vi bindings. Characters with the 8th bit set are written as M-<character>, and are referred to as metafied characters. The printable ASCII characters not mentioned in the list of emacs standard bindings are bound to the self-insert function, which just inserts the given character into the input line. In vi insertion mode, all characters not specifically mentioned are bound to self-insert. Characters assigned to signal generation by stty(1) or the terminal driver, such as C-Z or C-C, retain that function. Upper and lower case metafied characters are bound to the same function in the emacs mode meta keymap. The remaining characters are unbound, which causes readline to ring the bell (subject to the setting of the bell-style variable).

Emacs Mode


Emacs Standard bindings

"C-@"  set-mark
"C-A"  beginning-of-line
"C-B"  backward-char
"C-D"  delete-char
"C-E"  end-of-line
"C-F"  forward-char
"C-G"  abort
"C-H"  backward-delete-char
"C-I"  complete
"C-J"  accept-line
"C-K"  kill-line
"C-L"  clear-screen
"C-M"  accept-line
"C-N"  next-history
"C-P"  previous-history
"C-Q"  quoted-insert
"C-R"  reverse-search-history
"C-S"  forward-search-history
"C-T"  transpose-chars
"C-U"  unix-line-discard
"C-V"  quoted-insert
"C-W"  unix-word-rubout
"C-Y"  yank
"C-]"  character-search
"C-_"  undo
" " to "/"  self-insert
"0"  to "9"  self-insert
":"  to "~"  self-insert
"C-?"  backward-delete-char

Emacs Meta bindings

"M-C-G"  abort
"M-C-H"  backward-kill-word
"M-C-I"  tab-insert
"M-C-J"  vi-editing-mode
"M-C-M"  vi-editing-mode
"M-C-R"  revert-line
"M-C-Y"  yank-nth-arg
"M-C-["  complete
"M-C-]"  character-search-backward
"M-space"  set-mark
"M-#"  insert-comment
"M-&"  tilde-expand
"M-*"  insert-completions
"M--"  digit-argument
"M-."  yank-last-arg
"M-0"  digit-argument
"M-1"  digit-argument
"M-2"  digit-argument
"M-3"  digit-argument
"M-4"  digit-argument
"M-5"  digit-argument
"M-6"  digit-argument
"M-7"  digit-argument
"M-8"  digit-argument
"M-9"  digit-argument
"M-<"  beginning-of-history
"M-="  possible-completions
"M->"  end-of-history
"M-?"  possible-completions
"M-B"  backward-word
"M-C"  capitalize-word
"M-D"  kill-word
"M-F"  forward-word
"M-L"  downcase-word
"M-N"  non-incremental-forward-search-history
"M-P"  non-incremental-reverse-search-history
"M-R"  revert-line
"M-T"  transpose-words
"M-U"  upcase-word
"M-Y"  yank-pop
"M-\"  delete-horizontal-space
"M-~"  tilde-expand
"M-C-?"  backward-delete-word
"M-_"  yank-last-arg

Emacs Control-X bindings

"C-XC-G"  abort
"C-XC-R"  re-read-init-file
"C-XC-U"  undo
"C-XC-X"  exchange-point-and-mark
"C-X("  start-kbd-macro
"C-X)"  end-kbd-macro
"C-XE"  call-last-kbd-macro
"C-XC-?"  backward-kill-line

VI Mode bindings



VI Insert Mode functions

"C-D"  vi-eof-maybe
"C-H"  backward-delete-char
"C-I"  complete
"C-J"  accept-line
"C-M"  accept-line
"C-R"  reverse-search-history
"C-S"  forward-search-history
"C-T"  transpose-chars
"C-U"  unix-line-discard
"C-V"  quoted-insert
"C-W"  unix-word-rubout
"C-Y"  yank
"C-["  vi-movement-mode
"C-_"  undo
" " to "~"  self-insert
"C-?"  backward-delete-char

VI Command Mode functions

"C-D"  vi-eof-maybe
"C-E"  emacs-editing-mode
"C-G"  abort
"C-H"  backward-char
"C-J"  accept-line
"C-K"  kill-line
"C-L"  clear-screen
"C-M"  accept-line
"C-N"  next-history
"C-P"  previous-history
"C-Q"  quoted-insert
"C-R"  reverse-search-history
"C-S"  forward-search-history
"C-T"  transpose-chars
"C-U"  unix-line-discard
"C-V"  quoted-insert
"C-W"  unix-word-rubout
"C-Y"  yank
" "  forward-char
"#"  insert-comment
"$"  end-of-line
"%"  vi-match
"&"  vi-tilde-expand
"*"  vi-complete
"+"  next-history
","  vi-char-search
"-"  previous-history
"."  vi-redo
"/"  vi-search
"0"  beginning-of-line
"1" to "9"  vi-arg-digit
";"  vi-char-search
"="  vi-complete
"?"  vi-search
"A"  vi-append-eol
"B"  vi-prev-word
"C"  vi-change-to
"D"  vi-delete-to
"E"  vi-end-word
"F"  vi-char-search
"G"  vi-fetch-history
"I"  vi-insert-beg
"N"  vi-search-again
"P"  vi-put
"R"  vi-replace
"S"  vi-subst
"T"  vi-char-search
"U"  revert-line
"W"  vi-next-word
"X"  backward-delete-char
"Y"  vi-yank-to
"\"  vi-complete
"^"  vi-first-print
"_"  vi-yank-arg
"`"  vi-goto-mark
"a"  vi-append-mode
"b"  vi-prev-word
"c"  vi-change-to
"d"  vi-delete-to
"e"  vi-end-word
"f"  vi-char-search
"h"  backward-char
"i"  vi-insertion-mode
"j"  next-history
"k"  prev-history
"l"  forward-char
"m"  vi-set-mark
"n"  vi-search-again
"p"  vi-put
"r"  vi-change-char
"s"  vi-subst
"t"  vi-char-search
"u"  undo
"w"  vi-next-word
"x"  vi-delete
"y"  vi-yank-to
"|"  vi-column
"~"  vi-change-case

FILES

~/.inputrc: Individual readline initialization file

AUTHORS

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

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

BUG REPORTS

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

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

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