Line editing in Bash

You probably know the GNU Bash. Many people would say that it does not have many features or it is even user-unfriendly. I've already tried other POSIX-like shells, but I still stick with my favourite GNU Bash. (I think that fish is quite a good shell, but lacks flexibility of configuration that Bash does have.)

Bash uses the readline library to provide the line-editing features. Readline provides editing of the text you type in, history etc. It has many features, but a lot of them is hidden behind obscure keyboard shortcuts or configuration options.

This page tries to provide an overview of features provided by the readline, especially useful in the Bash. I attempted to order the sections of this page from the most basic operations to more advanced and obscure features.

The listing of the shortcuts is not complete. Refer to readline and Bash manuals for complete lists of the shortcuts.

Few notes

Keyboard shortcuts

We will use three modifier keys: shift, control and alt (also called Meta). I will follow Emacs conventions of keyboard shortcut notation, since this notation is also used by the readline docs and the keyboard shortcuts are significantly influenced by the Emacs. Do not expect CUA-like keyboard shortcuts you know from Windows or many other contemporary desktop environments. The keyboard shortcuts were designed before any common convention was formed.

Notation of keyboard shortcuts I will use:

Shortcut	Description
a	A single key “a”, without any modifier keys or Caps Lock.
C-a or ^A	Control-a (case-insensitive)
M-A	Meta-a (Alt-a)
A	Uppercase “A” (Shift-a)
C-A	Control-Shift-A (assuming disabled Caps Lock)
[	That key that sends character “[” on your keyboard layout
^[	Escape
C-a a	Control-a followed by letter “a”

Also note that the keyboard shortcuts are processed on level of text, not keycodes or even scancodes. This means that your local keyboard mapping and Caps Lock state is applied before the Readline processes the keyboard shortcuts. Also, Control performs bitwise and operation with number 0x1f on the character code, therefore all shortcuts with Control are case-insensitive.

The Meta (Alt) key is usually implemented by prefixing all individual key codes with escape character (^[, 0x1b). When you do not have Alt key or your terminal emulator is broken, you can prefix each of the shortcuts manually with a press of the Escape key. This is useful when using terminal emulators on Android devices, where support of the Alt key is frequently broken or half-functioning.

All keys that do not have a place in the ASCII character set and do not produce a text characters produce some terminal escape sequences. I will call such keys keypad keys, for historical reasons – you can frequently find this terminology in documentation of terminal-based software.

Emacs key mnemonics

Many of keyboard shortcuts inherited from Emacs can be remembered by a letter (usually the initial one) in word describing action performed by the key. I will try to emphasize this by underlining some letters in the description of the keys.

Flow control characters

By default, you will be unable to use any shortcuts that contain ^Q or ^S, because these work as a flow control characters. Pressing ^S stops the terminal output (but your input is still processed!). Press ^Q to restore the terminal output.

Line-editing features

Cursor movement

Group	Keypad key	… that sends sequence	Shortcut	Action
History navigation	↑	^[A	C-p	Previous item in the history
	↓	^[B	C-n	Next item in the history
			C-r	Reverse iterative search in history
Character movement	←	^[D	C-b	Back, one character
	→	^[C	C-f	Forward, one character
Word movement	M-←	^[[1;3D	M-b	Back, one word
	M-→	^[[1;3C	M-f	Forward, one word

History navigation

Press C-r to enter iterative search mode. Type a substring of a command you want to edit. Press ^R again to search for the previous item. Exit by pressing any key that does not type text.

Note that the history editing edits the history in-place. When you move to another history item and return to the item that you have edited, the edits will remain there.

In theory, C-s will perform a forward iterative search. That means that you will move to later items in the history. But since the terminal is usually configured to interpret ^S as a flow control character, it will stop the terminal output and the shell could appear “broken” in eyes of novice users.

Arbitrary character insertion

Press ^V followed by any key. The key code will be inserted literally, without interpreting it as a shortcut. You can use this to insert control characters, such as Escape.

Example

Try running this command, but instead of each ^[ press C-v Escape:

echo "^[31mUwU^[0m"

After executing this, a red “UwU” should appear in your terminal. See also Terminal escape sequences.

History replay

When you move to some command in your history and press C-o, the command will get executed and when it ends, the Bash will pre-enter the next command from the history. When you reach the original end of the history, the first command will be pre-entered in the prompt again.

Example

Run this first:

echo hello
echo people
echo there

Then press ↑ or C-p three times.

After that, press C-o repeatedly. These three commands will be executed in the same order, one command at each press of C-o.

Real world example

This is useful when you want to build and run your program. The commands executed in the “loop” could be these two:

make -j4
./my-program

Alternative keys to run a command

Pressing C-m sends Return (\r in C parlance) and C-j sends Line Feed (\n). Both of them can be used to run the command you have typed so far.

This is useful when the Return (Enter) key is too far to be reached easily. ☺