31.3.1 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 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
setcommand within the init file. The syntax is simple:
set variable value
Here, for example, is how to change from the default Emacs-like key binding to use
viline editing commands:
set editing-mode vi
Variable names and values, where appropriate, are recognized without regard to case. Unrecognized variable names are ignored.
Boolean variables (those that can be set to on or off) are set to on if the value is null or empty, on (case-insensitive), or 1. Any other value results in the variable being set to off.
A great deal of run-time behavior is changeable with the following variables.
- 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.
- If set to on, Readline attempts to bind the control characters
treated specially by the kernel's terminal driver to their Readline
- The string to insert at the beginning of the line when the
insert-commentcommand is executed. The default value is
- If set to on, Readline performs filename matching and completion
in a case-insensitive fashion.
The default value is off.
- The number of possible completions that determines when the user is
asked whether the list of possibilities should be displayed.
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.
This variable must be set to an integer value greater than or equal to 0.
A negative value means Readline should never ask.
The default limit is
- If set to on, Readline will convert characters with the
eighth bit set to an ascii key sequence by stripping the eighth
bit and prefixing an <ESC> character, converting them to a
meta-prefixed key sequence. The default value is on.
- 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-modevariable 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.
- 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.
- If set to on, tilde expansion is performed when Readline
attempts word completion. The default is off.
- If set to on, the history code attempts to place point at the
same location on each history line retrieved with
next-history. The default is off.
- 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.
- If set to on, Readline will enable eight-bit input (it
will not clear the eighth bit in the characters it reads),
regardless of what the terminal claims it can support. The
default value is off. The name
meta-flagis a synonym for this variable.
- The string of characters that should terminate an incremental search without
subsequently executing the character as a command (see Searching).
If this variable has not been given a value, the characters <ESC> and
C-J will terminate an incremental search.
- Sets Readline's idea of the current keymap for key binding commands.
viis equivalent to
emacsis equivalent to
emacs-standard. The default value is
emacs. The value of the
editing-modevariable also affects the default keymap.
- If set to on, completed directory names have a slash
appended. The default is on.
- 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.
- If set to on, completed names which are symbolic links
to directories have a slash appended (subject to the value of
mark-directories). The default is off.
- This variable, when set to on, causes Readline to match files whose
names begin with a . (hidden files) when performing filename
completion, unless the leading . is
supplied by the user in the filename to be completed.
This variable is on by default.
- 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.
- If set to on, Readline uses an internal
more-like pager to display a screenful of possible completions at a time. This variable is on by default.
- If set to on, Readline will display completions with matches
sorted horizontally in alphabetical order, rather than down the screen.
The default is 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.
The default value is 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.
The default value is off.
- 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 need to find 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 on a line in the init file the name of the key you wish to bind the command to, a colon, and then the name of the command. The name of the key can be expressed in different ways, depending on what you find most comfortable.
In addition to command names, readline allows keys to be bound to a string that is inserted when the key is pressed (a macro).
- 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).
A number of symbolic character names are recognized while processing this key binding syntax: DEL, ESC, ESCAPE, LFD, NEWLINE, RET, RETURN, RUBOUT, SPACE, SPC, and TAB.
- "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 again 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:
- control prefix
- meta prefix
- an escape character
- <">, a double quotation mark
- <'>, a single quote or apostrophe
In addition to the gnu Emacs style escape sequences, a second set of backslash escapes is available:
- alert (bell)
- form feed
- carriage return
- horizontal tab
- vertical tab
- the eight-bit character whose value is the octal value nnn
(one to three digits)
- the eight-bit character whose value is the hexadecimal value HH (one or two hex 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: