CS Blog

CS-348 Quarter 1

I was looking at some git articles and found a neat command. The article in question is How I use the Git for-each-ref command for DevOps and it covers the for-each-ref subcommand. We've always used git branch to list out all the commits and, in most use cases, that's all that's needed. But some use cases may need more data within those commits or even filter them. We can write some shell script with a bunch of pipes to do so but the solution is built-in. The article explored a use case where a bug occurred in some branch that Quality Assurance received but no one knows which build has it. The author then used for-each-ref to cleanly grab every branch then filter for the ones QA would've received as they follow a naming convention so they may get looked at properly.

The snippet and its output are the following:

git for-each-ref --format='%(refname:short) (%(committerdate))' \
								 --sort='-committerdate' \
								 'refs/remotes/**/deployment-qa-*'
origin/deployment-qa-c6e94a5 (Wed May 12 19:40:46 2021 -0500)
origin/deployment-qa-b70b438 (Fri Apr 23 15:42:30 2021 -0500)
origin/deployment-qa-347fc1d (Thu Apr 15 17:11:25 2021 -0500)
origin/deployment-qa-c1df9dd (Wed Apr 7 11:10:32 2021 -0500)
origin/deployment-qa-260f8f1 (Tue Apr 6 15:50:05 2021 -0500)

We can tell what it does at a glance and can pipe the output into whatever internal tooling we have to make it fancier looking. Doing it by hand not knowing that this is a feature would've been a lot more confusing to sift through. In fact, a manual implementation of that same snippet would look like this:

for ref in .git/refs/remotes/*/deployment-qa-*; do
    [ -f "$ref" ] || continue  # skip non-files

    branch=${ref#.git/refs/remotes/}
    sha=$(cat "$ref")
    date=$(git show -s --format="%cd" "$sha")

    echo "$branch ($date)"
done | sort -r

It's still legible and can be expanded upon but the previous snippet trumps is not only more concise but for-each-ref provides greater functionality. Its --format flag eliminates the risk of typoing something within the $() of every variable declaration. And after getting the output formatted as needed, it can be forced into a Python or Pearl-compatible string via --python and --pearl for easy piping. You can also set how many branches should be listed, where to start at, merge-specific filtering, and a lot more. All of these features are written in the documentation.

I don't see myself using this command too often but it definitely shows the maturity of git. There's tons of features that we don't learn unless we go out of our ways to dig for them.