I use the terminal to navigate and perform actions as much as I can, as I find I can work much more quickly. However, I'm always learning new shortcuts that make my life much easier.

This post assumes you're running your bash prompt in emacs mode. If you're not sure, then it's probably in emacs mode, as it's the default

Recall and Substitution Commands

Probably my most commonly used shortcut is the !! command. It executes the last command typed. This is particularly useful on Ubuntu, e.g.

$ apt-get install cowsay
E: Could not open lock file /var/lib/dpkg/lock - open (13 Permission denied)
E: Unable to lock the administration directory (/var/lib/dpkg/), are you root?

I missed out sudo, which is needed to install.

$ sudo !!
sudo apt-get install cowsay
[sudo] password for michael:

By using the !! command, it places the previous command after sudo, which executes the command.

You can use a similar command to access any previous commands in your bash history. It is !-n, where n is the number of lines to go back. This means that !! and !-1 are equivalent, and !-2 means the command you executed before the most recently executed one.

Finally, there's a third substitution shortcut that's rarely known. Imagine this situation:

$ ps -u micheal | grep firefox
ERROR: User name does not exist.

I have a rogue Firefox instance that I need to kill. However, I accidentally typo'd my username, and there's a few ways I could fix it. I could press the up arrow, then navigate to that point in the line and fix it. Or, I could use substitution.

$ ^ea^ae
ps -u michael | grep firefox
 1134 ?        03:55:11 firefox

Those are the three commands I use most when navigating around my system and executing commands.

Shortcuts

There's also a few shortcuts that allow you to save time when typing commands in the first place. If you type fast, and find yourself getting two letters in the wrong order, you can press ctrl+t to swap them around.

Another shortcut which I find useful, is using lists. Imagine we have three files, mon.txt, tues.txt and weds.txt, and we want to move them into folder X. The following two commands are identical:

$ mv {mon,tues,weds}.txt X
$ mv mon.txt tues.txt weds.txt X

Finally, when on the command line, press CTRL+R to bring up your bash history prompt. Type part of the command you're looking for and press enter to execute the one that's matches, or press right to load the command for editing. This is useful for me when I have to ssh into a server, and I can only remember the first two digits of it's IP address. I simply have to hit CTRL+R and type "ssh 87" then press enter.

Aliases?

Of course, some of the above problems could be solved easily (and permanently) with aliases. For example, look at some of these example aliases for solving some of the problems presented above:

alias apt-get='sudo apt-get $1'

This solves the problem where I sometimes forget to type sudo.

alias sshDelta ='ssh 87.255.255.255'

This one makes it easy to ssh into the server (In this name, named Delta)

To get these working, make sure .bash_aliases is enabled in ~/.bashrc, then add them to .bash_aliases. You can then either close the terminal and open it again, or type source .~/.bash_aliases to read the file.

Attribution

I learnt a lot of this browsing around the internet over the last few months and idling in #geekup on Freenode. However, The Geek Stuff has a very comprehensive list of commands to help master your command line history, which refreshed my memory and taught me about the !-n syntax for accessing previous history lines.

Are there any command line tips you use frequently that want to share? Let us know in the comments :)

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