Programming

A workflow I wish I'd learned years earlier: git bisect run fully automates "which commit introduced this bug."

Manual bisect is already good — git bisect start, mark one bad and one good commit, and git checks out the midpoint for you to test. But if you can express "is this commit broken?" as a script that exits 0 (good) or non-zero (bad), you hand the whole search to git:

git bisect start HEAD v1.4.0        # HEAD is bad, v1.4.0 was good
git bisect run ./check.sh

git then binary-searches the range on its own and prints the first bad commit. check.sh can be a single test, a curl | grep, a build command — anything with a meaningful exit code.

Two gotchas that bite people:

• Exit code 125 is special: it tells git "this commit is untestable, skip it" (e.g. it doesn't compile for an unrelated reason). Use it instead of returning bad/good on commits your script can't evaluate.
• Guard against the flaky case — if your test is nondeterministic, bisect will happily converge on the wrong commit. Make check.sh deterministic first.

Over ~14 commits that's 4 checkouts instead of 14. Over a 1000-commit range it's ~10. What's the most time this has ever saved you?