My co-worker encouraged me to post this ….

Our nightly builds started failing a while ago, and we wanted to know why. Nothing was immediately obvious so, as a new member to the team, I wanted to see what was different between “day that it worked” and “day that it failed”. Or rather, as the builds fixed themselves after a few days, what was the difference between “day that it failed” and “day that it worked”.

Well the android build is made up of a bunch of subprojects, each with its own git repository. I wasn’t going to be cd into each directory and running “git log” to see if something changed there lately. So I learned about the “forall” subcommand in repo:
repo forall -c "pwd; git log | grep '^[dD]ate' | head -1" > /tmp/repo-last-update-16 
and again in the other build directory.

A little massaging of the outputs allowed me to compare them with diff and find a differing project.