Tuesday, 25 November 2008

Handy shortcuts in the bash shell

You may have noticed that I've pushed the use of the command line (or, to give it the proper name, the shell), over graphical utilities much of the time. This is deliberate - the shell is a fast, flexible and powerful interface. Once you've got a bit of experience, most things can be done a lot faster from the shell. Now that I'm used to apt-get and apt-cache, I almost never use Synaptic to install anything in Ubuntu as it's so much quicker and more efficient to use the shell.

There are several different shells available for Unix-like operating systems, such as the original Bourne shell, the C shell, the Korn shell (used in Sun's Solaris operating system, among others), the Z shell (which was used in early versions of Mac OS X), and others. Linux uses the bash shell (in common with more recent versions of Mac OS X and OpenSolaris), which stands for Bourne Again SHell. This is a free software rewrite of the Bourne shell, but with many of the more advanced features of other shells incorporated into it.

Bash includes a number of very handy shortcuts that really make a difference. Don't you hate having to type out filenames in full, such as package-0.8.1.tar.gz? Me too, but bash has an answer - autocompletion.

To use autocompletion, start typing a command, then press tab. If bash has enough to confirm what you're typing, it will automatically fill in the rest. For example:
sudo apt-get upd

Press tab here, and there's enough for bash to autocomplete to this:
sudo apt-get update

But what if you enter this:
sudo apt-get up

Here, there's more than one option. The final word could be update or upgrade, so bash doesn't know how to complete it. Instead, when you press tab, you'll hear a bell to show that bash can complete it. But press it again and you'll be shown a list of possible options, as in this example:
matthew@morpheus:~$ sudo apt-get up
update upgrade
matthew@morpheus:~$ sudo apt-get up

Note that although the line you were on ends, what you'd entered is copied to the new line so you don't have to retype it.

This works for filenames and commands, so you could use autocompletion in this example with the file package-0.8.1.tar.gz:
tar -xzf pack

Assuming there wasn't another file in the current directory whose first four letters were pack, this would autocomplete fine. You can also use autocompletion to fill in the names of folders. If you had a path to a file like this:
You could type one or two letters for each folder within the path, and press tab to fill in the rest of the folder name.

Autocompletion is a very handy feature in bash that can save you a lot of time, and makes using the shell a lot quicker and easier.

There are some other handy keyboard shortcuts you might want to be aware of. I've mentioned in a previous post that if you've started a process and would like to cancel it, you can press Ctrl-C and the process will stop dead.

Another handy shortcut is Ctrl-D, which acts the same as the exit command ie. it closes down the shell you've been using. However, it's possible to have one shell running inside another so this doesn't necessarily mean it closes the terminal emulator. For instance, if you open the terminal, you have one shell running. If you then enter bash and press enter, this opens a new shell and places you in it (this would be a subshell). By pressing Ctrl-D here, you'd be returned to your original shell. Pressing it again would close the terminal.

Another is Ctrl-L, which clears the terminal. A similar effect can be had by entering the clear command.

If you want to repeat previous commands, you can use the up and down cursor keys to scroll through previously used commands in the current session. For example, if you entered ls, then less text.txt, you could press up twice to get ls again.

Finally, two things you may want to know are how to copy and paste. Copying is Ctrl-Shift-C, while pasting is Ctrl-Shift-V or Shift-Insert.

If you're interested in learning a few more shortcuts, check out this link for more details. I'd recommend you get familiar with at least the commands mentioned above as these are extremely labour-saving. Also, over the next few posts I plan to delve into the shell a little more and you'll probably find these shortcuts invaluable.

I'd also recommend that you find a good command-line editor as these are invaluable for editing configuration files. I highly recommend you take the time to learn Vim using the tutorial mode built into it (just open the shell and enter vimtutor), as although Vim may seem tough at first, it's one of those things like touch-typing - at first it slows you down, but soon enough you'll be faster than you ever were. It's also a great text editor for if you want to program - I'm currently learning Python and I find it incredibly useful. But if you try it and it really doesn't work for you, try nano instead. Even though it's a command-line editor, it's simple to use.

Finally, if you're really finding bash an uphill struggle and would prefer something that really goes out of its way to help beginners, why not try fish? Short for Friendly Interactive SHell, this is a good choice for newbies, and a great learning tool. But don't give up on bash! Use fish to learn the ropes if you like it, but bash is more powerful and flexible in the long term. You can get fish from the repositories:
sudo apt-get install fish

Then, to run it, just enter the following:

This will set fish running as a subshell within bash.