Aliases and bash customization

Overview

Teaching: 15 min
Exercises: 5 min

Questions

• How do I customize my bash environment?

Objectives

• Create aliases.

• Add customizations to the .bashrc and .bash_profile files.

• Change the prompt in a bash environment.

Bash allows us to customize our environments to fill our own particular needs.

Aliases

Sometimes we need to use long commands that have to be typed over and over again. Fortunately, the alias command allows us to create shortcuts for these long commands.

As an example, let’s create aliases for going up one, two, or three directories.

alias up='cd ..'
alias upup='cd ../..'
alias upupup='cd ../../..'

Let’s try these commands out.

cd /usr/local/bin
upup
pwd

/usr

We can also remove a shortcut with unalias.

unalias upupup

If we create one of these aliases in a bash session, they will only last until the end of that session. Fortunately, bash allows us to specify customizations that will work whenever we begin a new bash session.

Bash customization files

Bash environments can be customized by adding commands to the .bashrc, .bash_profile, and .bash_logout files in our home directory. The .bashrc file is executed whenever entering interactive non-login shells whereas .bash_profile is executed for login shells. If the .bash_logout file exists, then it will be run after exiting a shell session.

Let’s add the above commands to our .bashrc file.

echo "alias up='cd ..'" >> ~/.bashrc
tail -n 1 ~/.bashrc

alias up='cd ..'

We can execute the commands in .bashrc using source

source ~/.bashrc
cd /usr/local/bin
up
pwd

/usr/local

Having to add customizations to two files can be cumbersome. It we would like to always use the customizations in our .bashrc file, then we can add the following lines to our .bash_profile file.

if [ -f $HOME/.bashrc ]; then
        source $HOME/.bashrc
fi

Adding an alias to .bashrc

Add one or more alias to your .bashrc file. Aliases can be very helpful little things. Too many and complicated aliases can become difficult to manage. Also do keep in mind not to overwrite existing commands. Bash won’t complain, but confusion could be real. Try to keep it simple and memorable.

Fox example, what would happen if you would create the following alias?

alias cd='ls -lA'

Best not to try?

Consider following aliases, is any of those worthy addition to your .bashrc file? What do they do?

alias ll='ls -l'
alias rm='rm -v'
alias psu='ps -u $USER -f'

Solution

It would mask the cd command and your session would no longer have direct access to it. Essentially you would get stuck in the folder you are currently because any attempt to use cd would look to Bash as ls -lA command with the same arguments. So instead of navigating to destination folder you would see a list of all the files in that folder. DO NOT TRY THIS AT HOME :)

# one of the most common ls alias, show files and folder long list format
alias ll='ls -l'
# make rm command alway verbose
alias rm='rm -v'
# show $USER running processes
alias psu='ps -u $USER -f'

Customizing your prompt

We can also customize our bash prompt by setting the PS1 system variable. To set our prompt to be $ , then we can run the command

export PS1="$ "

To set the prompt to $ for all bash sessions, add this line to the end of .bashrc.

Further bash prompt customizations are possible. To have our prompt be username@hostname[directory]: , we would set

export PS1="\u@\h[\W]: "

where \u represents username, \h represents hostname, and \W represents the current directory.

Key Points

• Aliases are used to create shortcuts or abbreviations

• The .bashrc and .bash_profile files allow us to customize our bash environment.

• The PS1 system variable can be changed to customize your bash prompt.