Ubuntu – find a complete reference for the $PS1 variable

bashps1

The default PS1 variable on my machine (Kubuntu 13.10) is this:

\[\e]0;\u@\h: \w\a\]${debian_chroot:+($debian_chroot)}\u@\h:\w\$

I'm looking for a reference for how the $PS1 variable works that, at a minimum, allows me to understand the above PS1 variable.

Best Answer

References

So far, there hasn't been a single reference for everything that can go in a Bash prompt - but as it's a feature that has evolved over decades and probably varies from distro to distro, maybe that's too much to ask. I've tried to summarise what I found most useful here.

This how-to is the most complete, but is very long and rambling. Some of the more useful sections:

Section 2.4 and 2.5 explain the basics of setting PS1, including the (printable) escape characters.
Section 3.4 explains why \[ and \] are necessary.
Section 6 explains all the main (non-printable) escape sequences you might want to use, including setting the colour of the prompt and the title of an xterm window.

This guide explains how ${} works in Bash in general, and this Ask Ubuntu question explains a bit more about how that works with debian_chroot.

Between those, I think every character in the default Ubuntu PS1 variable is explained.

Explanation of the Ubuntu prompt

There are three parts to the prompt:

\[\e]0;\u@\h: \w\a\] sets the title bar of an xterm window:
- \[ starts a section of non-printable characters
- \e]0; is the escape sequence for 'set xterm title' (I believe numbers other than 0 will set other xterm properties, though I haven't tested this)
- \u@\h: \w the title to use (see below for \u, \h and \w)
- \a marks the end of the title
- \] marks the end of non-printable characters
${debian_chroot:+($debian_chroot)} expands to the value of $debian_chroot in parentheses if $debian_chroot is set. See this question for more information about $debian_chroot.
\u@\h:\w\$ is the prompt itself:
- \u expands to the current username
- \h expands to the current hostname
- \w expands to the current working directory
- \$ expands to # for root and $ for all other users

Related Solutions

Ubuntu – How to keep the coloring in bash when using `sudo -i`

Add the PS1 line to /root/.bashrc.

The reason why the color goes back to default is because when you do sudo -i, it "simulates" a root login, and in turn sources (applies) root's .bashrc, which brings the color back to the default. So adding the PS1 line to root's .bashrc should do the trick.

Ubuntu – Where is the PATH variable being set

The PATH could be set in any of the various files bash reads when it starts. To find them all, run this:

grep --color -H 'PATH=' ~/.bashrc ~/.profile ~/.bash_profile ~/bash.login \
                     ~/.bash_aliases /etc/bash.bashrc /etc/profile \
                     /etc/profile.d/* /etc/environment 2> /dev/null

Those are the standard ones. If you are also sourcing other files from one of those, things can get more complex.

Anyway, to fix it—assuming you haven't done anything to the global files in /etc/—you can run this:

sed -i '/PATH=/d' ~/.bashrc ~/.profile ~/.bash_profile ~/bash.login ~/.bash_aliases

That will delete any lines setting PATH from those files. Now, add the right one in the right place:

pp='PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/home/jgrande/android-sdk-linux/platform-tools:/usr/lib/jvm/java-7-openjdk-amd64/bin/:/usr/lib/jvm/java-7-openjdk-amd64/jre/bin'
[[ -e '~/.bash_profile' ]] && echo "$pp" >> ~/bash_profile ||
                              echo "$pp" >> ~/.profile

When invoked as a login shell, bash reads .bash_profile if present and, if not, it reads ~/.profile (it will ignore .profile if .bash_login is present but I assume it isn't). So, the commands above will first save your desired path as $pp and then check whether a ~/.bash_profile exists, add the path definition to it if it does and, if it doesn't, it will add it to ~/.profile.

In the future, to avoid this kind of issue, use a function to add directories to your $PATH. Add these lines to your ~/.profile:

pathmunge () 
{ 
    if ! echo $PATH | /bin/egrep -q "(^|:)$1($|:)"; then
        if [ "$2" = "after" ]; then
            PATH=$PATH:$1;
        else
            PATH=$1:$PATH;
        fi;
    fi
}

Then, to add something to the beginning of your $PATH, add this line to ~/.profile:

pathmunge "/path/to/foo"

And to add it to the end:

pathmunge "/path/to/foo" after

The function will only add a new directory to the $PATH if it isn't already there.