Bash Reference Manual - 8. Command Line Editing

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8. Command Line Editing

This chapter describes the basic features of the GNU command line editing interface.

8.1 Introduction to Line Editing

The following paragraphs describe the notation used to represent keystrokes.

The text C-k is read as `Control-K' and describes the character produced when the k key is pressed while the Control key is depressed.

The text M-k is read as `Meta-K' and describes the character produced when the meta key (if you have one) is depressed, and the k key is pressed. If you do not have a meta key, the identical keystroke can be generated by typing ESC first, and then typing k. Either process is known as metafying the k key.

The text M-C-k is read as `Meta-Control-k' and describes the character produced by metafying C-k.

In addition, several keys have their own names. Specifically, DEL, ESC, LFD, SPC, RET, and TAB all stand for themselves when seen in this text, or in an init file (@xref{Readline Init File}).

8.2 Readline Interaction

Often during an interactive session you type in a long line of text, only to notice that the first word on the line is misspelled. The Readline library gives you a set of commands for manipulating the text as you type it in, allowing you to just fix your typo, and not forcing you to retype the majority of the line. Using these editing commands, you move the cursor to the place that needs correction, and delete or insert the text of the corrections. Then, when you are satisfied with the line, you simply press RETURN. You do not have to be at the end of the line to press RETURN; the entire line is accepted regardless of the location of the cursor within the line.

8.2.1 Readline Init File Syntax

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 (see section 8.2.2 Conditional Init Constructs). Other lines denote variable settings and key bindings.

Variable Settings

You can modify the run-time behavior of Readline by altering the values of variables in Readline using the set command within the init file. Here is how to change from the default Emacs-like key binding to use vi line editing commands:

set editing-mode vi

A great deal of run-time behavior is changeable with the following variables.

bell-style: 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' (the default), Readline attempts to ring the terminal's bell.
comment-begin: The string to insert at the beginning of the line when the insert-comment command is executed. The default value is "#".
completion-ignore-case: If set to `on', Readline performs filename matching and completion in a case-insensitive fashion. The default value is `off'.
completion-query-items: The number of possible completions that determines when the user is asked whether he wants to see the list of possibilities. If the number of possible completions is greater than this value, Readline will ask the user whether or not he wishes to view them; otherwise, they are simply listed. The default limit is 100.
convert-meta: 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 ESC character, converting them to a meta-prefixed key sequence. The default value is `on'.
disable-completion: 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. The default is `off'.
editing-mode: The editing-mode variable controls which default set of key bindings is used. By default, Readline starts up in Emacs editing mode, where the keystrokes are most similar to Emacs. This variable can be set to either `emacs' or `vi'.
enable-keypad: 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. The default is `off'.
expand-tilde: If set to `on', tilde expansion is performed when Readline attempts word completion. The default is `off'.
horizontal-scroll-mode: This variable can be set to either `on' or `off'. Setting it to `on' means that the text of the lines being edited will scroll horizontally on a single screen line when they are longer than the width of the screen, instead of wrapping onto a new screen line. By default, this variable is set to `off'.
keymap: Sets Readline's idea of the current keymap for key binding commands. Acceptable keymap names are 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 the editing-mode variable also affects the default keymap.
mark-directories: If set to `on', completed directory names have a slash appended. The default is `on'.
mark-modified-lines: This variable, when set to `on', causes Readline to display an asterisk (`*') at the start of history lines which have been modified. This variable is `off' by default.
input-meta: If set to `on', Readline will enable eight-bit input (it will not strip the eighth bit from the characters it reads), regardless of what the terminal claims it can support. The default value is `off'. The name meta-flag is a synonym for this variable.
output-meta: If set to `on', Readline will display characters with the eighth bit set directly rather than as a meta-prefixed escape sequence. The default is `off'.
print-completions-horizontally: If set to `on', Readline will display completions with matches sorted horizontally in alphabetical order, rather than down the screen. The default is `off'.
show-all-if-ambiguous: 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. The default value is `off'.
visible-stats: If set to `on', a character denoting a file's type is appended to the filename when listing possible completions. The default is `off'.

Key Bindings

The syntax for controlling key bindings in the init file is simple. First you have to know the name of the command that you want to change. The following sections contain tables of the command name, the default keybinding, if any, and a short description of what the command does. Once you know the name of the command, simply place the name of the key you wish to bind the command to, a colon, and then the name of the command on a line in the init file. The name of the key can be expressed in different ways, depending on which is most comfortable for you.

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, 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).

"keyseq": function-name or macro

keyseq differs from keyname above in that strings denoting an entire key sequence can be specified, by placing the key sequence in double quotes. Some GNU Emacs style key escapes can be used, as in the following example, but the special character names are not recognized.

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

In the above example, C-u is bound to the function universal-argument (just as it was in the first example), `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 following GNU Emacs style escape sequences are available when specifying key sequences:

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

In addition to the GNU Emacs style escape sequences, a second set of backslash escapes is available:

\a: alert (bell)
\b: backspace
\d: delete
\f: form feed
\n: newline
\r: carriage return
\t: horizontal tab
\v: vertical tab
\nnn: the character whose ASCII code is the octal value nnn (one to three digits)
\xnnn: the character whose ASCII code is the hexadecimal value nnn (one to three digits)

When entering the text of a macro, single or double quotes must be used to indicate a macro definition. Unquoted text is assumed to be a function name. In the macro body, the backslash escapes described above are expanded. Backslash will quote any other character in the macro text, including `"' and `''. For example, the following binding will make `C-x \' insert a single `\' into the line:

"\C-x\\": "\\"

8.2.2 Conditional Init 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 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 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 both 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 you can test for it. 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.

$include /etc/inputrc

8.2.3 Sample Init File

Here is an example of an inputrc file. This illustrates key binding, variable assignment, and conditional syntax.

# This file controls the behaviour of line input editing for
# programs that use the Gnu Readline library.  Existing programs
# include FTP, Bash, and Gdb.
#
# You can re-read the inputrc file with C-x C-r.
# Lines beginning with '#' are comments.
#
# First, include any systemwide bindings and variable assignments from
# /etc/Inputrc
$include /etc/Inputrc

#
# Set various bindings for emacs mode.

set editing-mode emacs 

$if mode=emacs

Meta-Control-h:	backward-kill-word	Text after the function name is ignored

#
# Arrow keys in keypad mode
#
#"\M-OD":        backward-char
#"\M-OC":        forward-char
#"\M-OA":        previous-history
#"\M-OB":        next-history
#
# Arrow keys in ANSI mode
#
"\M-[D":        backward-char
"\M-[C":        forward-char
"\M-[A":        previous-history
"\M-[B":        next-history
#
# Arrow keys in 8 bit keypad mode
#
#"\M-\C-OD":       backward-char
#"\M-\C-OC":       forward-char
#"\M-\C-OA":       previous-history
#"\M-\C-OB":       next-history
#
# Arrow keys in 8 bit ANSI mode
#
#"\M-\C-[D":       backward-char
#"\M-\C-[C":       forward-char
#"\M-\C-[A":       previous-history
#"\M-\C-[B":       next-history

C-q: quoted-insert

$endif

# An old-style binding.  This happens to be the default.
TAB: complete

# Macros that are convenient for shell interaction
$if Bash
# edit the path
"\C-xp": "PATH=${PATH}\e\C-e\C-a\ef\C-f"
# prepare to type a quoted word -- insert open and close double quotes
# and move to just after the open quote
"\C-x\"": "\"\"\C-b"
# insert a backslash (testing backslash escapes in sequences and macros)
"\C-x\\": "\\"
# Quote the current or previous word
"\C-xq": "\eb\"\ef\""
# Add a binding to refresh the line, which is unbound
"\C-xr": redraw-current-line
# Edit variable on current line.
"\M-\C-v": "\C-a\C-k$\C-y\M-\C-e\C-a\C-y="
$endif

# use a visible bell if one is available
set bell-style visible

# don't strip characters to 7 bits when reading
set input-meta on

# allow iso-latin1 characters to be inserted rather than converted to
# prefix-meta sequences
set convert-meta off

# display characters with the eighth bit set directly rather than
# as meta-prefixed characters
set output-meta on

# if there are more than 150 possible completions for a word, ask the
# user if he wants to see all of them
set completion-query-items 150

# For FTP
$if Ftp
"\C-xg": "get \M-?"
"\C-xt": "put \M-?"
"\M-.": yank-last-arg
$endif

8.3 Bindable Readline Commands

This section describes Readline commands that may be bound to key sequences.

8.3.1 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 letters and digits.
backward-word (M-b): Move back to the start of this, or the previous, word. Words are composed of letters and digits.
clear-screen (C-l): Clear the screen and redraw the current line, leaving the current line at the top of the screen.
redraw-current-line (): Refresh the current line. By default, this is unbound.

8.3.2 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 setting of the HISTCONTROL and HISTIGNORE variables. If this line was a history line, then restore the history line to its original state.
previous-history (C-p): Move `up' through the history list.
next-history (C-n): Move `down' through the history 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 the history as necessary. This is an incremental search.
non-incremental-reverse-search-history (M-p): Search backward starting at the current line and moving `up' through the history as necessary using a non-incremental search for a string supplied by the user.
non-incremental-forward-search-history (M-n): Search forward starting at the current line and moving `down' through the the history as necessary 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. By default, this command is unbound.
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. By default, this command is unbound.
yank-nth-arg (M-C-y): Insert the first argument to the previous command (usually the second word on the previous line). 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 last argument to the previous command (the last word of the previous history entry). With an argument, behave exactly like yank-nth-arg. Successive calls to yank-last-arg move back through the history list, inserting the last argument of each line in turn.

8.3.3 Commands For Changing Text

delete-char (C-d): Delete the character under the cursor. If the cursor is at the beginning of the line, there are no characters in the line, and the last character typed was not bound to delete-char, then return EOF.
backward-delete-char (Rubout): Delete the character behind the cursor. A numeric argument means to kill the characters instead of deleting them.
quoted-insert (C-q, C-v): Add the next character typed to the line verbatim. This is how to insert key sequences like C-q, for example.
self-insert (a, b, A, 1, !, ...): Insert yourself.
transpose-chars (C-t): Drag the character before the cursor forward over the character at the cursor, moving the cursor forward as well. If the insertion point is at the end of the line, then this transposes the last two characters of the line. 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, uppercase the previous word, but do not move the cursor.
downcase-word (M-l): Lowercase the current (or following) word. With a negative argument, lowercase the previous word, but do not move the cursor.
capitalize-word (M-c): Capitalize the current (or following) word. With a negative argument, capitalize the previous word, but do not move the cursor.

8.3.4 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 the cursor to the beginning of the current line. The killed text is saved on the kill-ring.
kill-whole-line (): Kill all characters on the current line, no matter where the cursor is. By default, this is unbound.
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 forward-word.
backward-kill-word (M-DEL): Kill the word behind the cursor. Word boundaries are the same as backward-word.
unix-word-rubout (C-w): Kill the word behind the cursor, using white space as a word boundary. The killed text is saved on the kill-ring.
delete-horizontal-space (): Delete all spaces and tabs around point. By default, this is unbound.
kill-region (): Kill the text between the point and the mark (saved cursor position). This text is referred to as the region. By default, this command is unbound.
copy-region-as-kill (): Copy the text in the region to the kill buffer, so it can be yanked right away. By default, this command is unbound.
copy-backward-word (): Copy the word before point to the kill buffer. The word boundaries are the same as backward-word. By default, this command is unbound.
copy-forward-word (): Copy the word following point to the kill buffer. The word boundaries are the same as forward-word. By default, this command is unbound.
yank (C-y): Yank the top of the kill ring into the buffer at the current cursor position.
yank-pop (M-y): Rotate the kill-ring, and yank the new top. You can only do this if the prior command is yank or yank-pop.

8.3.5 Specifying 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. By default, this is not bound to a key.

8.3.6 Letting Readline Type For You

complete (TAB): Attempt to do completion on the text before the cursor. This is application-specific. Generally, if you are typing a filename argument, you can do filename completion; if you are typing a command, you can do command completion; if you are typing in a symbol to GDB, you can do symbol name completion; if you are typing in a variable to Bash, you can do variable name completion, and so on. Bash attempts completion treating the text as a variable (if the text begins with `$'), username (if the text begins with `~'), hostname (if the text begins with `@'), or command (including aliases and functions) in turn. If none of these produces a match, filename completion is attempted.
possible-completions (M-?): List the possible completions of the text before the cursor.
insert-completions (M-*): Insert all completions of the text before point that would have been generated by possible-completions.
menu-complete (): Similar to complete, but replaces the word to be completed with a single match from the list of possible completions. Repeated execution of menu-complete steps through the list of possible completions, inserting each match in turn. At the end of the list of completions, the bell is rung and the original text is restored. An argument of n moves n positions forward in the list of matches; a negative argument may be used to move backward through the list. This command is intended to be bound to TAB, but is unbound by default.
complete-filename (M-/): Attempt filename completion on the text before point.
possible-filename-completions (C-x /): List the possible completions of the text before point, treating it as a filename.
complete-username (M-~): Attempt completion on the text before point, treating it as a username.
possible-username-completions (C-x ~): List the possible completions of the text before point, treating it as a username.
complete-variable (M-$): 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 command 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.
complete-into-braces (M-{): Perform filename completion and return the list of possible completions enclosed within braces so the list is available to the shell (see section 3.5.1 Brace Expansion).

8.3.7 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 save 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.

8.3.8 Some Miscellaneous Commands

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): Make the next character typed be metafied. This is for keyboards without a meta key. Typing `ESC f' is equivalent to typing `M-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 get back to the beginning.
tilde-expand (M-~): Perform tilde expansion on the current word.
set-mark (C-@): 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 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.
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. This command is unbound by default.
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. This command is unbound by default.
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. This command is unbound by default.
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 displayed, and the line is redrawn.
display-shell-version (C-x C-v): Display version information about the current instance of Bash.
shell-expand-line (M-C-e): Expand the line as the shell does. This performs alias and history expansion as well as all of the shell word expansions (see section 3.5 Shell Expansions).
history-expand-line (M-^): Perform history expansion on the current line.
magic-space (): Perform history expansion on the current line and insert a space (see section 7.3 History Expansion).
alias-expand-line (): Perform alias expansion on the current line (see section 5.9 Aliases).
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 relative to the current line from the history for editing. Any argument is ignored.
emacs-editing-mode (C-e): When in vi editing mode, this causes a switch back to emacs editing mode, as if the command `set -o emacs' had been executed.

8.4 Readline vi Mode

While the Readline library does not have a full set of vi editing functions, it does contain enough to allow simple editing of the line. The Readline vi mode behaves as specified in the POSIX 1003.2 standard.

In order to switch interactively between emacs and vi editing modes, use the `set -o emacs' and `set -o vi' commands (see section 5.5 The Set Builtin). The Readline default is emacs mode.

When you enter a line in vi mode, you are already placed in `insertion' mode, as if you had typed an `i'. Pressing ESC switches you into `command' mode, where you can edit the text of the line with the standard vi movement keys, move to previous history lines with `k' and subsequent lines with `j', and so forth.

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Bash Reference Manual - 8. Command Line Editing