Configuring Bash

If you’ve reached this page, you’re probably interested in how best to optimize your overall Bash experience. In addition to the things we talk about here, you should be sure to brush up on the lessons in the Bash topic. You’re almost sure to find something there that will be useful to customizing your terminal.

As we’ve mentioned a few times before, the file you’re going to be using abundantly to configure your prompt is the .bashrc file on Linux and the .bash_profile on OS X. There’s a good discussion of the underlying differences between these files here, but you don’t necessarily have to know what they are to be able to configure Bash. From here on out, we’ll use ~/.bashrc, though you should substitute ~/.bash_profile if you’re on OS X.

The Prompt

One of the most popular aspects of Bash to customize is the prompt. A quick Google search will turn up some vastly different Bash prompts; they should give you an idea of what’s possible. Since it’s so popular, there are lots of comprehensive resources online for how to get started configuring your prompt. Both of the following links provide an excellent resource for you to get started customizing your prompt. The first is more of a walkthrough, while the second is an interactive web app that lets you visualize and generate a Bash prompt.

• How to Customize the Command Prompt
  • You can probably find plenty of tutorials by searching for “customize Bash prompt” on Google. This was the best one I could find. It’s fairly comprehensive and it goes through plenty of examples and screenshots.
• Bash $PS1 Generator
  • This site (and the many like it) allow you visually configure your prompt, so that you don’t have to look up the specific escape sequences needed to turn on colors or bring up information about the shell.

You should definitely give these a read through. People take great pride in crafting a beautiful prompt, and it can be a really fun project to introduce you to some deeper features of Bash.

Tab Completion & The Prompt Line

By changing your Bash prompt, you get to customize the look of your command line. There are also a number of settings that let you configure the feel of your command line, controlling how you actually interact with it.

Tab Completion

You probably know by now that you can press TAB to have Bash automatically complete filenames. Bash’s tab completion functionality is actually much more sophisticated; properly configured, Bash can complete things like Git branches, package manager commands, flags to your favorite programs, and more. Getting this new configuration is actually quite simple. Add the following lines to your ~/.bashrc:

if [ -f /etc/bash_completion ]; then
  source /etc/bash_completion
fi

This runs a script that turns on more powerful Bash completion scripts.

If you’re on OS X, you’ll have to install Bash completion separately. If you haven’t already, go install Homebrew, then run

# Install updated bash and bash completion
brew install bash bash-completion

# Add the newly installed bash to the list of valid login shells
echo "$(brew --prefix)/bin/bash" | sudo tee -a /etc/shells

# Change your shell to the new bash
chsh -s "$(brew --prefix)/bin/bash"

Finally, add the following to your ~/.bash_profile:

if [ -f $(brew --prefix)/etc/bash_completion ]; then
  source $(brew --prefix)/etc/bash_completion
fi

Once again, this runs a script that turns on the more powerful Bash completion scripts.

From time to time when installing a piece of software, you might see something in a post-installation note about completion scripts having been installed. For example, when installing the most recent version of Git through Homebrew on OS X, the following message is printed:

Bash completion has been installed to:
  /usr/local/etc/bash_completion.d

This means you can now do things like git br<TAB> and have Bash complete that to git branch, as well as git branch ma<TAB> and have Bash complete that to git branch master.

With a little bit of digging, you’ll be able to find Bash completion scripts for many commonly used programs. They’ll either install themselves or require that you add a snippet similar to the one above to your ~/.bashrc.

Readline and the .inputrc

Tab completion isn’t the only way you interact with with the command line. Bash uses a library called GNU Readline for reading lines of text from the user; everything you type into Bash first is processed by Readline. Readline is incredibly configurable–for a complete list of options, see this page. Since Readline is actually its own program, it uses its own dotfile, named ~/.inputrc, a file which is used to configure all programs that use Readline. Since there are so many options that you can pass to it, I’ll summarize some that I’ve found most helpful.

Vim-Style “Menu” Tab Completion

Vim by default handles tab completion differently than the way Bash does; when you press TAB, it completes one whole filename instead of a prefix, and successive TABs cycle through the available options. To enable this in Bash, add these lines to your ~/.inputrc:

# Set up Vim-style tab completion
TAB: menu-complete
set show-all-if-ambiguous on

The first line binds the TAB key to the menu-complete functionality, which handles cycling through available options. The second line turns off the bell sound that would normally ring if you pressed TAB when there are still multiple options that could be completed.

Treat Symlinked Directories Like Directories

When tab-completing the name of a symbolic link, the default behavior is to treat it like a file. That is, once it has completed the name of the symbolic link, it puts a space between the end of the filename and your cursor. If the symlink was to a directory that you wanted to include in a longer path name, this isn’t the desired behavior. To have it print a / instead of a space, use this:

# If a tab-completed file is a symlink to a directory,
# treat it like a directory not a file
set mark-symlinked-directories on

Use GNU ls Colors When Tab-Completing

Normally when you press TAB to complete a filename, the files are all colored the same. However, when you run ls, all the files are colored according to the type of file that they are. To use these same colors when printing the completion options, add the following to your .inputrc:

# Use GNU ls colors when tab-completing files
set colored-stats on

Note: You can actually do a fair deal of configuration just on the colors that ls uses, such as highlighting images, movies, and PDFs in different colors. One project that does this particularly well is Solarized Color Theme for GNU ls. It assumes that you have GNU ls installed, so you’ll have to install it separately through Homebrew if you use OS X.

Vim-Style Line Editing

Hopefully by now you’re a Vim ninja! If so, you’ve probably come to understand just how awesome Vim’s composable, modal editing style can be. To gain access to the same vi-style key bindings when typing at the REPL, include this in your .inputrc:

# Edit with Vi keybindings
set editing-mode vi
set keymap vi

The Magic of rlwrap

Now you can use the power of Vi in Bash, Python, and any other program that uses Readline! If your stuck using a lesser program that doesn’t support readline out of the box (for example the SML/NJ REPL), you can simply preface that program with rlwrap when running it:

$ rlwrap sml

Not only does this give you access to all the configurations we just added to our ~/.inputrc, it also turns on command history, so you can scroll through all previously-run commands.

Aliases

Aliases are a way of making long commands short. The syntax is super simple, and they’re incredibly useful for speeding up your workflows.

Here’s the syntax:

alias <something short>="<something really long>"

And here’s an example:

# `git status` is a really frequently used command... Let's shorten it!
$ alias gs="git status"
$ gs
On branch master
Your branch is ahead of 'origin/master' by 1 commit.
  (use "git push" to publish your local commits)
nothing to commit, working directory clean

If we put alias gs="git status" in our ~/.bashrc, we’ll have access to this alias every time we log in!

Aliases are really useful for commands that take a lot of flags. For example, most people prefer to have ls colorize output, but this feature isn’t on by default—you have to set a flag. As such, most people have the following definition in their ~/.bashrc:

alias ls="ls --color=auto"

This “shadows” the ls command. Now when you enter ls at the command prompt, instead of running the ls command immediately, Bash first looks up the ls alias, substitutes the text ls for ls --color=auto, and then runs it. Note that this doesn’t break down if we pass an argument to ls; it will simply be tacked onto the end of the command. That is, ls ~/Documents just becomes ls --color=auto ~/Documents.

Environment Variables

There are loads of environment variables that can be used to configure your terminal setup. Changes to environment variables won’t persist across logins; if you want them to be available and set to the same value, you’ll have to add them to your ~/.bashrc.

One environment variable we’ve seen already is the PATH variable. Recall that this variable contains a list of colon-separated directories which Bash uses to locate runnable programs. Something common people like to do is to have their own directory, usually named ~/bin, to hold scripts and programs that they’d like to be easily accessible. To get this directory into the PATH variable, you’d add this line to your ~/.bashrc:

export PATH="$PATH:$HOME/bin"

This tacks $HOME/bin onto your normal PATH variable.

Oftentimes certain programs will need to have certain environment variables set in order to run correctly. If you read in the documentation that you need to do this for a program you want to use, all you have to do is change that variable in your ~/.bashrc to have it’s value set correctly every time you log in.