Keybinding and updating terminal text line in bash

tl;dr 1) bind -x '"<some character>":some-function'; 2) change the READLINE_LINE/READLINE_POINT variables in the script

Keybinding

This is a really cool feature that you can use to create/change the behaviour of keys in your terminal.

Before we proceed

Keep in mind that you can set the keybindings in your ~/.inputrc or ~/.bashrc (or any other file that is sourced on start).

Here we have two examples of setting the arrou up to get the previous command that matches the initial text written so far (kind of Ctrl+r). Just note that history-search-backward is a builtin function.

# ~/.inputrc
"\e[A":history-search-backward

# ~/.bashrc
bind -x '"\e[A":history-search-backward'

Here is a simple example using a custom function

# ~/.bashrc
__clear_screen__() {
  # clear all the content of current screen (same as reopen termial)
  clear && printf '\e[3J'
}

# "C-l" means `Ctrl+l`
# you can see more options/the syntax at https://www.computerhope.com/unix/bash/bind.htm
bind -x '"\C-l":__clear_screen__'

The READLINE_LINE and READLINE_POINT variables

Those variables just store the current text and the cursor position. Here is a simple example of dealing with them:

__print_letter_and_write_it__() {
  # just prints a
  echo $1

  # changes the content of input text
  READLINE_LINE="$READLINE_LINE$1"

  # puts the cursor after the letter `a`
  # without this, the cusrsor would end after the letter `a`
  # if you are not familiar with `${#READLINE_LINE}`, it just returns the length of the `READLINE_LINE` variable
  READLINE_POINT=${#READLINE_LINE}
}

# call `__print_letter_and_write_it__` with `a` as argument
bind -x '"a":__print_letter_and_write_it__ a'

Here you can see another example of dealing with binding keys and updating the input text, where I start fzf and update the text based on the user’s action.