bisect

Git · Reference cheat sheet

📋 Overview

git bisect binary-searches history to find the commit that introduced a bug. Mark commits good / bad (or old / new); automate with bisect run and a script that exits 0 (good) or non-zero (bad).

🔧 Core concepts

• Start — bisect start, then mark known bad and good endpoints.
• Midpoints — Git checks out a mid commit; you test and mark.
• Terms — good/bad or old/new (regression vs behavior change).
• Skip — untestable commits (bisect skip).
• Run — git bisect run ./test.sh automates the loop.

💡 Examples

git bisect start
git bisect bad HEAD
git bisect good v1.2.0

# manually test, then:
git bisect good   # or: git bisect bad

git bisect reset  # return to original branch

# Automated
git bisect start HEAD v1.2.0
git bisect run npm test
# script exit: 0 = good, 1-127 (not 125) = bad, 125 = skip

git bisect skip
git bisect log
git bisect replay bisect-log.txt

⚠️ Pitfalls

• Need a reliable test — flaky tests send bisect the wrong way.
• Shallow clones may lack enough history — deepen first.
• Skipped ranges can leave an ambiguous first-bad commit.
• Detached HEAD during bisect — don’t start new feature work mid-bisect.
• Build failures unrelated to the bug should skip or fix the script’s exit codes.

🔗 Related

• log.md
• blame.md
• checkout via branch.md
• reflog.md
• tag.md
• diff.md