Mercurial: The Definitive Guide

Flexible Diff Support with the extdiff Extension

Mercurial’s built-in hg diff command outputs plain text unified diffs.

$ hg diff
diff -r a6ba002523c0 myfile
--- a/myfile	Tue May 05 06:44:37 2009 +0000
+++ b/myfile	Tue May 05 06:44:37 2009 +0000
@@ -1,1 +1,2 @@
 The first line.
+The second line.

If you would like to use an external tool to display modifications, you’ll want to use the extdiff extension. This will let you use, for example, a graphical diff tool.

The extdiff extension is bundled with Mercurial, so it’s easy to set up. In the extensions section of your ~/.hgrc, simply add a one-line entry to enable the extension.

[extensions]
extdiff =

This introduces a command named extdiff, which by default uses your system’s diff command to generate a unified diff in the same form as the built-in hg diff command.

$ hg extdiff
--- a.a6ba002523c0/myfile	2009-05-05 06:44:37.769474821 +0000
+++ /tmp/extdiffXbMA0x/a/myfile	2009-05-05 06:44:37.677474721 +0000
@@ -1 +1,2 @@
 The first line.
+The second line.

The result won’t be exactly the same as with the built-in hg diff variations, because the output of diff varies from one system to another, even when passed the same options.

As the “making snapshot” lines of output above imply, the extdiff command works by creating two snapshots of your source tree. The first snapshot is of the source revision; the second, of the target revision or working directory. The extdiff command generates these snapshots in a temporary directory, passes the name of ...