onsub
This extension is not distributed with Mercurial.
Author: Martin Geisler
Download site: http://bitbucket.org/mg/onsub/
Overview
The onsub extension will traverse all subrepositories and execute a command in each.
This can be used to update all subrepositories with one command:
$ hg onsub "hg pull -u"
Configuration
Configure your .hgrc to enable the extension by adding following lines:
[extensions] onsub = path/to/onsub/onsub.py