Effective bash shorthand

29 May 2009

Let me tell you how to maximize your productivity on the Bourne Again SHell while minimizing your effort. bash has a ton of tricks and shortcuts that allow you to command it with little effort, and I intend to show you the features that help me day in and day out.

Today I’m going to explain the use of features like history, brace and file expansion, and other tricks by example and give you references for later.

Master your history

Those who forget history are doomed to repeat it. This is arguably one of the best productivity enhancing features of any shell.

You can check your history with the history command, which prints your last 500 commands (or so) by default. Alternatively, you can filter the list:

# Print last 10 entries
history 10

# searches history for cmd
history | grep cmd

Each entry has a number, which you can then execute with !<number>

Now suppose I want to copy a file to a directory and then change to that directory. The quick way to do that with history is:

cp myfile.txt my/directory/path
cd !$  # cd my/directory/path

or if I forget to run a command as super-user:

vi /etc/fstab  # oops!
sudo !!  # sudo vi /etc/fstab

to execute the last command starting with "mount", since I don’t want to type it all out:

# Previously...
mount 192.168.0.100:/my/path/to/music /media/music

# Later...
!mount
# Repeats last mount command

Note that I often (but not always) prefer Ctrl-R, which will search history as you type. As an added bonus you can view the command before executing it.

Other examples:

echo foo -a bar baz
# prints "foo -a bar baz"

echo !:3-4
# prints "bar baz"

!-2
# executes "echo foo -a bar baz"

!^:p
# prints "foo", but MUCH cooler than "echo ..." 
^ba^ya
# executes "echo foo -a yar baz"

!?bar
# executes "echo foo -a bar baz"

Quick reference

`!!`	expands to the last command and all arguments
`!-3`	3rd-to-last command and all arguments
`!^`	first argument of the last command in history
`!:2`	2nd argument of the last command
`!$`	last argument of the last command
`!*`	all arguments of the last command, but not the command itself
`!42`	expands to the 42nd command in the history list
`!foo`	last command beginning with "foo"
`!?baz`	last command containing "baz"
`^foo^bar`	last command with the first occurrence of "foo" replaced with "bar"
`!:gs/foo/bar`	last command with all occurrences of "foo" replaced with "bar"
`<any_above>:p`	prints command without executing

Helpful .bashrc entries for history

Copy and paste these into ~/.bashrc

# Don't put duplicate lines in the history
export HISTCONTROL=ignoredups
# Ignore successive duplicate entries.
export HISTCONTROL=ignoreboth

# Store a lot history entries in a file for grep-age
shopt -s histappend
export HISTFILE=~/long_history
export HISTFILESIZE=50000

# No reason not to save a bunch in history
# Takes up several more MBs of RAM now, oOOOooh
export HISTSIZE=9999

# Ignore dupe commands and other ones you don't care about
export HISTIGNORE="&:[ ]*:exit"

Another neat trick with .inputrc

If you are still particularly fond of the up and down arrows, copy and paste the following into a ~/.inputrc file. This will allow you to start typing a command and then hit the up-arrow to search backwards through your history for commands starting with what you typed. I prefer other methods usually but this is pretty cool, huh?

"\eOA": history-search-backward
"\e[A": history-search-backward
"\eOB": history-search-forward
"\e[B": history-search-forward
"\eOC": forward-char
"\e[C": forward-char
"\eOD": backward-char
"\e[D": backward-char

Brace expansions

No shorthand list would be complete without the (in)famous brace expansions. Basically, they allow you to specify part(s) of an command to repeat substituting different values of a set within braces. Let me show you what I mean:

# Quickly make a backup
cp file.txt{,.bak}
# Equivalent to 'cp file.txt file.txt.back'

This is obviously very useful to prevent having to repeat parts of files or directory paths.

Suppose I wanted to make a template folder structure, I could make most of the directories I need with:

mkdir -p {src,test}/com/eriwen/{data,view}

This will expand every combination so I end up with src/com/eriwen/data, src/com/eriwen/view, test/com/eriwen/data, and so forth. Being able to create a template directory structure with one line is a big time saver!

Better filename expansion

I'm sure you often use the * operator to match files beginning or ending with something, but bash goes far beyond that. It should be noted, though, at some point a good find | grep is more powerful and useful. See Find is a beautiful tool for more information.

In addition to wildcards with *, you can use ? to match any single character. You can also limit matching to certain characters with []. For example:

ls
# prints "myfile netbeans.conf netbeans-6.5rc2 netbeans-6.5 netbeans-6.7 src"
ls netbeans-6.?
# matches "netbeans-6.5 netbeans-6.7"
ls netbeans-6.[1-5]*
# matches "netbeans-6.5rc2 netbeans-6.5"

.bashrc entries for better filename expansion

# Include dot (.) files in the results of expansion
shopt -s dotglob
# Case-insensitive matching for filename expansion
shopt -s nocaseglob
# Enable extended pattern matching
shopt -s extglob

cd shorthand

There are a couple quick tricks to change to oft-used directories. For example:

# Lame way to go home
cd ~

# The cool way
cd

You can also switch to the previous directory with cd - like so:

pwd  # prints /home/eriwen/src
cd /my/webserver/directory

# Do something...

cd -
# Now I'm back in /home/eriwen/src

To get more advanced with this, try mastering your directory stack with pushd and popd.

Conclusion

Effective use of history, brace expansions, and other shortcuts will to save you a lot of time. However, nothing is more productive than no typing. Automating things is best where possible. If you can’t automate, use smart aliases.

I know I did not cover tilde expansions, shell parameter expansions or bash key commands. You will want to check those out as well, but I find them less useful than what I’ve covered here.

Have any quick shortcuts you love? Share them in the comments!