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{{Article summary text|Improving readline over its default capabilities.}}
 
{{Article summary text|Improving readline over its default capabilities.}}

Revision as of 15:33, 13 June 2012

Summary help replacing me
Improving readline over its default capabilities.
Important pages
Official site
Related
Bash

Readline is a library by the GNU Project, used by Bash and other CLI-interface programs to edit and interact with the command line. Before reading this page please refer to the library home page as only subtle configuration will be introduced here.

Command-line editing

By default Readline uses Emacs style shortcuts for interacting with command line. However, vi style editing interface is also supported. If you are a vi or vim user, you may want to put the following line to your ~/.inputrc to enable vi-like keybindings:

set editing-mode vi

Alternatively, to use the vi-like keybindings, you may add the following line to your ~/.bashrc:

set -o vi

You may find either vi or emacs cheat sheets useful.

History

Usually, pressing the up arrow key will cause the last command to be shown regardless of what has been typed so far. However, users may find it more practical to list only past commands that match the current input.

For example, if the user has typed the following commands:

  • ls /usr/src/linux-2.6.15-ARCH/kernel/power/Kconfig
  • who
  • mount
  • man mount

In this situation, when typing ls and pressing the up arrow key, current input will be replaced with man mount, the last performed command. Had history search been enabled, only past commands beginning with ls (the current input) would've been shown, in this case ls /usr/src/linux-2.6.15-ARCH/kernel/power/Kconfig.

You can enable this mode by adding the lines below to /etc/inputrc or ~/.inputrc:

"\e[A":history-search-backward
"\e[B":history-search-forward

If you are using vi mode, you can add the following lines to ~/.inputrc (from this post):

set editing-mode vi
$if mode=vi
set keymap vi-command
# these are for vi-command mode
"\e[A": history-search-backward
"\e[B": history-search-forward
set keymap vi-insert
# these are for vi-insert mode
"\e[A": history-search-backward
"\e[B": history-search-forward
$endif

If you chose to add these lines to ~/.inputrc, it is recommended that you also add the following line at the beginning of this file to avoid strange things like this:

$include /etc/inputrc

Alternatively, one can use reverse-search-history (incremental search) by pressing Template:Keypress+Template:Keypress, which does not search based on previous input but instead jumps backwards in the history buffer as commands are typed in a search term. Pressing Template:Keypress+Template:Keypress again during this mode will display the previous line in the buffer that matches the current search term, while pressing Template:Keypress+Template:Keypress (abort) will cancel the search and restore the current input line. So in order to search through all previous mount commands, press Template:Keypress+Template:Keypress, type 'mount' and keep pressing Template:Keypress+Template:Keypress until the desired line is found.

The forward equivalent to this mode is called forward-search-history and is bound to Template:Keypress+Template:Keypress by default. Beware that most terminals override Template:Keypress+Template:Keypress to suspend execution until Template:Keypress+Template:Keypress is entered. (This is called XON/XOFF flow control). For activating forward-search-history, either disable flow control by issuing:

$ stty -ixon

or use a different key in inputrc. For example, to use Template:Keypress+Template:Keypress which is not bound by default:

"\es":forward-search-history

History search

Avoid duplicates

If you repeat the same command several times, they will all be appended in your history. To prevent this, add to your ~/.bashrc:

export HISTCONTROL=ignoredups

Avoid whitespaces

To disable logging blank commands add this to your ~/.bashrc:

export HISTCONTROL=ignorespace

If your ~/.bashrc already contains

export HISTCONTROL=ignoredups

replace it with

export HISTCONTROL=ignoreboth

Macros

Readline also supports binding keys to keyboard macros. For simple example, run this command in Bash:

bind '"\ew":"\C-e # macro"'

or add the part within single quotes to inputrc:

"\ew":"\C-e # macro"

Now type a line and press Template:Keypress+Template:Keypress. Readline will act as though Template:Keypress+Template:Keypress (end-of-line) had been pressed, appended with ' # macro'.

Use any of the existing keybindings within a readline macro, which can be quite useful to automate frequently used idioms. For example, this one makes Template:Keypress+Template:Keypress+Template:Keypress append "| less" to the line and run it (Template:Keypress+Template:Keypress is equivalent to Template:Keypress):

"\e\C-l":"\C-e | less\C-m"

The next one prefixes the line with 'yes |' when pressing Template:Keypress+Template:Keypress+Template:Keypress, confirming any yes/no question the command might ask:

"\e\C-y":"\C-ayes | \C-m"

This example wraps the line in su -c '', if Template:Keypress+Template:Keypress is pressed:

"\es":"\C-a su -c '\C-e'\C-m"

As a last example, quickly send a command in the background with Template:Keypress+Template:Keypress+Template:Keypress, discarding all of its output:

"\e\C-b":"\C-e > /dev/null 2>&1 &\C-m"

Tips and tricks

Disabling control echo

Due to an update to readline, the terminal now echoes ^C after Template:Keypress+Template:Keypress is pressed. For users who wish to disable this, simply add the following to ~/.inputrc:

set echo-control-characters off