Command Line Editing

Command Line Editing

When you make a mistake in typing out a command, the bash shell's got you covered – you don't need to erase everything and start from scratch. You can also pull up a past command and tweak it to craft a new one.

Out of the box, bash employs command-line editing inspired by the emacs text editor. If you've had a play with emacs before, then many of the keystrokes mentioned here might be familiar to you.

If you prefer vi for editing shell command lines, you can easily make that happen. Add the following line to the .bashrc file in your home directory: set -o vi From then on, every time you launch a shell, you'll be in familiar territory with those vi commands ready to edit!

To do the editing, you can use a combination of control keys, meta keys, and arrow keys. For example:

• Ctrl + f means to hold down the Ctrl key, and type f

• Alt + f means to hold down the Alt key, and type f

Instead of the Alt key, your keyboard may use a Meta key or the Esc key. On a Windows keyboard, you can use the Windows key.

Let's Give it a Try!

To try out a bit of command-line editing, enter the following command:

ls /usr/bin | sort -f | less

This command:

1. Lists the contents of the /usr/bin directory

2. Sorts the contents in alphabetical order (regardless of case)

3. Pipes the output to less

The less command displays the first page of output, after which you can go through the rest of the output one line (press Enter) or one page (press spacebar) at a time. Simply press q when you are finished.

Now, let's change this command, altering /usr/bin to /bin. You can use the following steps to change the command:

1. Press the up arrow (↑) key This displays the most recent command from your shell history

2. Press Ctrl + a This moves the cursor to the beginning of the command line

3. Press Ctrl + f or the right arrow (→) key Repeat this command a few times to position the cursor under the first slash (/)

4. Press Ctrl + d Type this command four times to delete /usr from the line

5. Press Enter This executes the command line

When you're tweaking a command line, you can type regular characters at any point, with your new characters appearing at the location of your text cursor. You can use right → and left ← arrows to move the cursor from one end to the other on the command line.

You can also press the up ↑ and down ↓ arrow keys to step through your command history and select one for editing.