git-bisect – Find by binary search the change that introduced a bug

Git even offers a binary search within commits to locate the single guilty commit that introduced a bug.

You run your test again and find that this commit is broken, so you tell Git that with git bisect bad:

It turns out there is no issue here, and you tell Git that by typing git bisect good and continue your journey:

The molecular orbital with the highest energy has two nodes that bisect the O–O \(\sigma\) bonds; it is a \(\pi\)* antibonding orbital.

In fact, if you have a script that will exit 0 if the project is good or non-0 if the project is bad, you can fully automate git bisect.

The bisect command does a binary search through your commit history to help you identify as quickly as possible which commit introduced an issue.

The ancient Greek mathematicians knew how to bisect an angle (divide it into two angles of equal measure) using only a compass and straightedge, but could only trisect certain angles.

The molecular orbital with the highest energy has two nodes that bisect the O–O σ bonds; it is a π* antibonding orbital.

When you’re finished, you should run git bisect reset to reset your HEAD to where you were before you started, or you’ll end up in a weird state:

The git bisect tool is an incredibly helpful debugging tool used to find which specific commit was the first one to introduce a bug or problem by doing an automatic binary search.

This example uses bisect() to look up a letter grade for an exam score (say) based on a set of ordered numeric breakpoints: 90 and up is an ‘A’, 80 to 89 is a ‘B’, and so on:

If you don’t know what is breaking, and there have been dozens or hundreds of commits since the last state where you know the code worked, you’ll likely turn to git bisect for help.