Subversion allows to use a custom command for displaying diffs using svn diff --diff-cmd <cmd>. I have been using diff-cmd=colordiff in my ~/.subversion/config for quite some time now. This is really useful, but occasionally I would also like to use vimdiff to get a nice side-by-side diff.

Although this sounds quite easy at first, there are some hurdles. Subversion expects the given command to adhere to the GNU diff parameters, that means it expects it to understand and parse the labels it passes before the actual filenames. This works fine for colordiff, but not vimdiff which only wants the old and new filenames.

For a better diff experience with svn, I set up the following shell function which let’s me choose the program I want to use for diffing.

First, I need a new wrapper script at ~/libexec/svndiff which takes the actual diff program as first option, ignores the GNU diff labels and calls that program passing old and new filename.

#!/bin/bash
BIN=$1
shift 5
$BIN "$@"

Then I define this shell alias in my ~/.bashrc to extend the functionality of the svn command:

function svn() {
    case "$1" in
        diff-plain)
            shift;
            `which svn` diff --diff-cmd diff $@
            ;;
        diff-color)
            shift;
            `which svn` diff --diff-cmd colordiff $@
            ;;
        diff-vim)
            shift;
            `which svn` diff --diff-cmd $HOME/libexec/svndiff -x vimdiff $@
            ;;
        diff-filemerge)
            shift;
            `which svn` diff --diff-cmd $HOME/libexec/svndiff -x opendiff $@
            ;;
        *)
            `which svn` $@
            ;;
    esac
}

Now I can choose the program I find best suited for the current task in a very simplified manner, for example svn diff-vim -c1337.