content/blog/2009/03/mercurial-bash-prompts.html @ 0b8539e28640

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{% hyde
    title: "Mercurial Bash Prompts"
    snip: "Always know where you are."
    created: 2009-03-17 21:34:55
    categories: ["programming"]
%}

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I've been spending a lot of time in the Terminal lately. I use bash, and it
lets you configure the prompt pretty much however you want. I won't go into
how to do the most basic configuration here - if you want to get up to speed
check out this [guide][].

In this post I'm just going to talk about one simple addition that I
personally find very helpful: displaying the current branch of a [Mercurial][]
repository.

Update: the hg-prompt Extension
---------------

I swear, this is the last time I'm updating this entry. I went ahead and made
an extension for Mercurial called
[hg-prompt](http://stevelosh.com/projects/hg-prompt/) that does everything
much more elegantly. **Use that instead!**

[guide]: http://www.ibm.com/developerworks/linux/library/l-tip-prompt/
[Mercurial]: {{links.mercurial}}
[git version]: http://gist.github.com/31631

My Starting Point
-----------------

Here's what my prompt looked like a couple of days ago:

![My bash prompt without the branch displayed](/media/images{{parent_url}}/prompt-without-branch.png "My bash prompt without the branch displayed.")

Here's the code in my `.bashrc` file to create it. I've stripped out the color
information to save space.

    :::bash
    export PS1='\n\u at \h in \w\n$ '

I use the same prompt on every computer I work with, so with this prompt I can
see which user I'm logged in as, which machine I'm on, and where in the
filesystem I am. It's a lot of useful information at a glance but doesn't seem
too cluttered.

I have a linebreak in there because the filesystem path can get pretty long.
If I kept it all on one line most of my commands would be wrapped around
anyway, which I find harder to read.

Adding the Mercurial Branch
---------------------------

I use Mercurial for version control, and I use branches quite a bit when I'm
developing. One problem with this is that it's easy to forget which branch I'm
on at a given moment. I *could* just use `hg branch` to find out, but that
gets tedious to type, even when aliased to something like `hb`.

A few days ago I got the idea that I could just display the current branch on
my prompt whenever I'm in a directory that's part of a repository. Here's what
my prompt looks like now:

![My bash prompt with the branch displayed](/media/images{{parent_url}}/prompt-with-branch.png "My bash prompt with the branch displayed.")

And here's the code in my `.bashrc` that does it:

    :::bash
    hg_in_repo() {
        hg branch 2> /dev/null | awk '{print "on "}'
    }

    hg_branch() {
        hg branch 2> /dev/null | awk '{print $1}'
    }

    export PS1='\n\u at \h in \w $(hg_in_repo)$(hg_branch)\n$ '

The `on branchname` piece is only displayed when you're in a directory that's
part of a Mercurial repository.

I've split it up into two separate functions because I wanted to have `on` and
`branchname` displayed in two different colors. I couldn't seem to include the
color codes in the awk command, so I split it up and put the colors in the
export statement with the rest of them. If you don't care about colors (or
don't mind having both words the same color) you can just collapse it into one
function.

Updated: Is It Dirty?
---------------------

After I posted this entry Matt Kemp commented with a link to a [git
version][]. One feature that version has is a simple indicator of whether or
not the repository you're in is dirty. I ported it to Mercurial and here's the
result:

![My bash prompt with the branch and dirty indicator displayed](/media/images{{parent_url}}/prompt-with-dirty.png "My bash prompt with the branch and dirty indicator displayed.")

And the code in `.bashrc`:

    :::bash
    hg_dirty() {
        hg status --no-color 2> /dev/null \
        | awk '$1 == "?" { print "?" } $1 != "?" { print "!" }' \
        | sort | uniq | head -c1
    }
    
    hg_in_repo() {
        [[ `hg branch 2> /dev/null` ]] && echo 'on '
    }

    hg_branch() {
        hg branch 2> /dev/null
    }

    export PS1='\n\u at \h in \w $(hg_in_repo)$(hg_branch)$(hg_dirty)\n$ '

This gives you a `?` after the branch when there are untracked files (and
*only* untracked files), and a `!` if there are any modified, tracked files.

Updated: Bookmarks Too!
----------------

I've added another piece to show bookmarks as well. I've also figured out how
to add colors directly in the functions, so here's the (much nicer) updated
code all at once:

    :::bash
    DEFAULT="[37;40m"
    PINK="[35;40m"
    GREEN="[32;40m"
    ORANGE="[33;40m"
    
    hg_dirty() {
        hg status --no-color 2> /dev/null \
        | awk '$1 == "?" { unknown = 1 } 
               $1 != "?" { changed = 1 }
               END {
                 if (changed) printf "!"
                 else if (unknown) printf "?" 
               }'
    }
    
    hg_branch() {
        hg branch 2> /dev/null | \
            awk '{ printf "\033[37;0m on \033[35;40m" $1 }'
        hg bookmarks 2> /dev/null | \
            awk '/\*/ { printf "\033[37;0m at \033[33;40m" $2 }'
    }
    
    export PS1='\n\e${PINK}\u \
    \e${DEFAULT}at \e${ORANGE}\h \
    \e${DEFAULT}in \e${GREEN}\w\
    $(hg_branch)\e${GREEN}$(hg_dirty)\
    \e${DEFAULT}\n$ '

These are some pretty simple changes but they help keep me sane. One thing to
be aware of: if you use all of these it does slow down the rendering of the
prompt by a tiny, but noticeable, amount. I'm not the strongest bash scripter,
so if there's a better way to do this (or a way that will make it faster and
reduce the delay) please let me know!

**UPDATE:** Matt Kemp posted a link to a [git version][] of this below. If you
use git, check it out! One thing that version has that I didn't think of is an
indicator of whether the repository is dirty (has uncommitted changes). I'm
going to go ahead and steal that idea for my prompt too.

**UPDATE:** By request, I've written [an entry about the
colors](/blog/entry/2009/3/18/candy-colored-terminal/).

**UPDATE:** Kevin Bullock pointed out that the Python interpreter needed to be
started a bunch of times which will degrade performance. I've changed up the
"dirty" code a bit to reduce the number of interpreters needed. It's still not
as efficient as his version, but I think it's about as good as I'm going to
get if I want separate colors for the pieces and don't want to rely on an
external script.

**FINAL UPDATE:** I made an extension for Mercurial called
[hg-prompt](http://stevelosh.com/projects/hg-prompt/) that does everything
much more elegantly. **Use that instead!**

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