Ian Obermiller

Part time hacker, full time dad.

Side-by-side diffs for Mercurial (hg)


UPDATE: This is easier now! See my new post, "Side-by-side diffs for Mercurial (hg) & icdiff revisited".

Ever wish for hg diff in side-by-side view? I find it much easier to scan, assuming you have the horizontal real-estate in your terminal. Here is a simple guide to setting up side-by-side diffs in Mercurial on Linux/OSX:

1. Install icdiff

The grunt of this work will be done by icdiff, an excellent tool by Jeff Kaufman. Download and install icdiff, making sure /usr/local/bin is in your $PATH.

2. Adapter scripts

Since icdiff only operates on individual files, we need to provide an adapter for it to work with directories. We'll use a modified version of Bryan O'Sullivan's hg-interdiff script. Drop this into ~/scripts/hg-icdiff, and then run chmod +x ~/scripts/hg-icdiff to make it executable:

#!/usr/bin/env python
# Adapter for using interdiff with mercurial's extdiff extension.
# Copyright 2006 Bryan O'Sullivan <bos@serpentine.com>
# This software may be used and distributed according to the terms of
# the GNU General Public License, incorporated herein by reference.

import os, sys

def walk(base):
    # yield all non-directories below the base path.
    for root, dirs, files in os.walk(base):
        for f in files:
            path = os.path.join(root, f)
            yield path[len(base)+1:], path
        if os.path.isfile(base):
            yield '', base

# create list of unique file names under both directories.
files = dict(walk(sys.argv[1]))
files = files.keys()

def name(base, f):
    if f:
        path = os.path.join(base, f)
        path = base
    # interdiff requires two files; use /dev/null if one is missing.
    if os.path.exists(path):
        return path
    return '/dev/null'

ret = 0

for f in files:
    if os.system('icdiff "%s" "%s"' % (name(sys.argv[1], f),
                                          name(sys.argv[2], f))):
        ret = 1


Next, we want this to be piped into less for easy paging, so put the following code in ~/scripts/hg-icdiff-wrapper, and also chmod +x it. The -F parameter makes less not page if the output fits in the screen.

$HOME/scripts/hg-icdiff "$@"|less -F -X

3. Mercurial settings

Next, lets configure Mercurial so that it knows about our script. Add the following to your ~/.hgrc (note the absolute path; I was not able to get it working with tilde ~ or $HOME):



You can now replace diff in your Mercurial commands with icdiff, and it will do a side-by-side diff instead of inline.

4. Aliases

Finally, since hg icdiff is too long, add the following aliases to your ~/.bashrc or ~/.zshrc:

# side-by-side diffs for uncommitted files
alias ic='hg icdiff'

# diff all changes since the base revision, including uncommitted
# (from master if you are using bookmarks, for example)
alias ica='hg icdiff -r .^'

# diff the existing changes, excluding uncommitted
alias ice='hg icdiff --ch .'