Friday, 14 March 2008

GNU Readline Library Short Description

GNU Readline is a software library that provides a set of functions that allow users to edit command lines as they are typed in.

Every program that uses this library provides the same user command line interface improving consistency between applications.

It is part of the GNU Project and it is licensed under the GPL.

Current version is 5.2 and it is used in projects like bash.

There are two editing modes available: Emacs (default) and Vi

Readline library includes additional functions to maintain a list of previously-entered command lines.
Exec this command to obtain more info about this feature:
$help history


In Debian and Ubuntu this library is packed in readline-common package.
$sudo aptitude install readline-common

Once installed, you can access a complete documentation using info command:
$info rluserman


C-k means while ctrl key is mantained pressed, depress 'k' key.
M-k means while "meta" key is pressed, depress 'k' key.

Usually "meta" refers to ALT key, but if you have no meta key you can use ESC key instead.

Emacs mode commmands:


C-b Move back the cursor one character.
C-f Move one character forward.
DEL or Backspace Delete the character placed left at the cursor.
C-d Delete the character underneath the cursor.
C-_ or C-x C-u Undo the last editing command.

C-a Move to the beginning of the line.
C-e Move to the end of the line.
M-f Move forward a word.
M-b Move backward a word.
C-l Clear the screen, reprinting the current line at the top.

Killing and yanking (cutting and pasting) commands

C-k Kill the text from the current cursor position to the end of the line.
M-d Kill from the cursor to the end of the current word.
M-DEL Kill from the cursor the start of the current word.
C-w Kill from the cursor to the previous whitespace.

After killing(cutting) text, we yank(paste) it back into the line.

C-y Yank the most recently killed text back into the buffer at the cursor.
M-y Rotate the kill-ring, and yank the new top. You can only do this if the prior command is C-y or M-y.

Searching commands

C-r Searchs backwards on the previous commands you typed.
C-s Perform a forward search from the command line history you are now.

Passing arguments to a command

e.g: M-2 3 C-d means delete next 23 characters on input line.


GNU Readline keybindings and more can be changed editing ~/.initrc or /etc/initrc files.

GNU Readline Official page
GNU Readline (Wikipedia)
Official online Readline documentation

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