Readline Init File Syntax - Debugging with GDB

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26.3.1 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 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 prefixing 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.
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.
isearch-terminators: 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.
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.
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 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 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
\": <">, 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:

\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\\": "\\"