vamseeachanta 3. Git Bisect (+2)
3. Git Bisect
Basic Bisect:
# Start bisect
git bisect start
# Mark current version as bad
git bisect bad
# Mark known good commit
git bisect good v1.0.0
# Git checks out a commit - test it
# If bad:
git bisect bad
# If good:
git bisect good
# Continue until found
# Git will show: "abc123 is the first bad commit"
# End bisect
git bisect reset
Automated Bisect:
# Create test script
cat > test-bug.sh << 'EOF'
#!/bin/bash
# Return 0 if good, non-zero if bad
npm test -- --grep "specific test"
EOF
chmod +x test-bug.sh
# Run automated bisect
git bisect start
git bisect bad HEAD
git bisect good v1.0.0
git bisect run ./test-bug.sh
# Git will find the bad commit automatically
git bisect reset
Bisect with Skip:
# If commit can't be tested (won't build)
git bisect skip
# Skip range of commits
git bisect skip abc123..def456
Bisect Log and Replay:
# Save bisect session
git bisect log > bisect.log
# Replay session
git bisect replay bisect.log
4. Git Rerere (Reuse Recorded Resolution)
Enable Rerere:
# Enable globally
git config --global rerere.enabled true
# Check status
git config --get rerere.enabled
Using Rerere:
# When you resolve a conflict, git records the resolution
git merge feature-branch
# Resolve conflicts...
git add .
git commit
# Next time same conflict occurs, git auto-applies resolution
git merge another-branch
# "Resolved 'file.txt' using previous resolution."
# If auto-resolution is wrong, forget it
git rerere forget path/to/file
Rerere Management:
# View recorded resolutions
ls .git/rr-cache/
# Clean old resolutions
git rerere gc
# Show diff of recorded resolution
git rerere diff
5. Git Reflog
Basic Reflog:
# Show reflog
git reflog
# Show reflog with dates
git reflog --date=relative
# Show reflog for specific ref
git reflog show feature-branch
# Output
# abc123 HEAD@{0}: commit: Latest commit
# def456 HEAD@{1}: checkout: moving from main to feature
# ghi789 HEAD@{2}: commit: Previous commit
Recovery with Reflog:
# Recover deleted branch
git reflog
# Find last commit of deleted branch: abc123
git checkout -b recovered-branch abc123
# Undo hard reset
git reflog
# Find state before reset: HEAD@{2}
git reset --hard HEAD@{2}
# Recover lost stash
git fsck --unreachable | grep commit
git show <commit-hash>
git stash apply <commit-hash>
# Recover from bad rebase
git reflog
# Find pre-rebase state: HEAD@{5}
git reset --hard HEAD@{5}
Reflog Expiration:
# Check expiration settings
git config --get gc.reflogexpire # Default: 90 days
git config --get gc.reflogexpireunreachable # Default: 30 days
# Extend reflog retention
git config --global gc.reflogexpire 180.days