Adventures in Mercurial

I adore Git, but have needed to ramp up my Mercurial (Hg) skills recently to dig prior work related to my current tasks out of a repo’s history. Here are some things I’m learning:

Command Equivalences

As this tutorial so helpfully explains, the two VCSes aren’t all that dissimilar under their hoods. I condensed the command comparison table into a single page and printed it out for quick reference; a PDF ishere.

Clone

The thing I want to clone lives at http://hg.mozilla.org/hgcustom/version-control-tools/file/tip/autoland .

Trying to clone the full URL yields a 404, but snipping the URL back to the top-level directory gets me the repo:

$ hg clone http://hg.mozilla.org/hgcustom/version-control-tools/ destination directory: version-control-tools requesting all changes adding changesets adding manifests adding file changes added 4574 changesets with 10874 changes to 1971 files updating to bookmark @ 1428 files updated, 0 files merged, 0 files removed, 0 files unresolved $ ls version-control-tools

Examine Log

hg log | less shows me that each commit’s summary in this repo includes the part of the codebase it touches, and a bug number.

hg log | grep autoland: | less gives me the summaries of every commit that touched autoland, but I cannot show a commit from summary alone.

The Hg book helped me construct a filter that will show a unique revision ID onthe same line as each description.

hg log --template '{rev} {desc}\n' | grep autoland: is much more useful. It gives me the local ID of each changeset whose description included “autoland:”.

From here, I can use a bit more grep to narrow down the list of matching messages, then I’m ready to examine commits.

Examining Commits

That {rev} in my filter was the “repository-local changeset revision number”. For these examples I’ll examine revision 2589.

hg status --change 2589 lists the files that were touched by that revision, and hg export 2589 yields a full diff of the changes introduced.

This gets me enough information to make an appropriate set of changes, run the tests, and create my own commits!