গিট ইন্টারভিউ প্রশ্ন 2026: মার্জ, রিবেস, রিসেট এবং ব্রাঞ্চিং

# merge: combines two branches, preserves full history
git checkout feature
git merge main
# Creates a merge commit — shows when branches diverged

# rebase: moves/replays commits on top of another branch
git checkout feature
git rebase main
# Linear history — as if feature branched off current main

# When to use merge:
# - Integrating feature branches to main (preserves history)
# - Public/shared branches (never rebase!)
# - When you want to see branch history

# When to use rebase:
# - Keeping feature branch up to date with main
# - Cleaning up local commits before PR
# - Squashing minor fix commits

# Golden rule: never rebase commits that have been pushed to shared branches

# HEAD = pointer to current commit (usually points to branch tip)
cat .git/HEAD  # ref: refs/heads/main  (pointing to main branch)

# Detached HEAD: HEAD points directly to a commit, not a branch
git checkout abc123  # checking out a specific commit
# HEAD is now at abc123 (detached)
# Any commits made won't belong to any branch!

# To save work in detached HEAD:
git checkout -b new-branch  # create branch from current position

# Common cause: git checkout <tag> or git checkout <commit-hash>

# git reset: move HEAD backward (rewrites history)
git reset --soft HEAD~1    # undo commit, keep changes staged
git reset --mixed HEAD~1   # undo commit, keep changes unstaged (DEFAULT)
git reset --hard HEAD~1    # undo commit AND discard changes (DESTRUCTIVE)

# NEVER use --hard on shared branches!

# git revert: create a new commit that undoes a previous commit
git revert abc123          # safe for shared branches
# Creates commit: "Revert 'feature: add user auth'"

# Use reset for: local commits you want to undo
# Use revert for: commits already pushed to shared branches

# Temporarily save uncommitted changes
git stash push -m "WIP: half-done feature"
git stash list                           # see all stashes
git stash pop                            # apply latest + remove
git stash apply stash@{0}               # apply without removing
git stash drop stash@{0}               # delete a stash

# Stash specific files
git stash push -m "CSS fix" -- styles.css components/Button.css

# Include untracked files
git stash push -u -m "including new files"

# Common workflow:
# 1. Working on feature-A
# 2. Urgent fix needed on feature-B
# git stash (save feature-A work)
# git checkout feature-B
# ... fix ...
# git checkout feature-A
# git stash pop (restore feature-A work)

# Interactive rebase — squash last 3 commits
git rebase -i HEAD~3

# Editor opens:
# pick abc123 feat: add login form
# pick def456 fix: correct validation
# pick ghi789 fix: typo in error message

# Change to:
# pick abc123 feat: add login form
# squash def456 fix: correct validation
# squash ghi789 fix: typo in error message

# Result: one clean commit with combined message

# Alternative: squash merge (GitHub/GitLab button)
# When merging PR, select "Squash and merge"
# All commits become one commit in main

# Apply a specific commit from another branch
git log --oneline feature-branch  # find the commit hash
git cherry-pick abc123            # apply just that commit

# Common use: apply a hotfix to multiple release branches
git checkout release/2.0
git cherry-pick fix/critical-bug-abc123
git checkout release/1.9
git cherry-pick fix/critical-bug-abc123

# Cherry-pick a range
git cherry-pick abc123..def456  # applies all commits in range

# If conflicts arise
git cherry-pick --continue  # after resolving conflicts
git cherry-pick --abort     # cancel cherry-pick

GitFlow (complex, stable releases):
  main          — production
  develop       — integration
  feature/xxx   — feature branches
  release/1.0   — release preparation
  hotfix/xxx    — urgent fixes

GitHub Flow (simple, continuous delivery):
  main          — always deployable
  feature/xxx   — short-lived feature branches
  Pull Request → Code Review → Merge to main → Deploy

Trunk-Based Development (very short-lived branches):
  main (trunk)  — everyone commits daily
  feature/xxx   — max 1-2 days old, use feature flags

2026 recommendation: GitHub Flow or Trunk-Based for most teams

# .gitignore tells git which files to ignore
# Never commit:
# - Secrets/credentials (.env files!)
# - Dependencies (node_modules/, vendor/)
# - Build artifacts (dist/, __pycache__/)
# - OS files (.DS_Store, Thumbs.db)
# - IDE files (.idea/, .vscode/ — optional)

# Example .gitignore
*.env
*.env.*
node_modules/
dist/
build/
.DS_Store
__pycache__/
*.pyc
*.pem
*.key

# Already committed? Remove from tracking:
git rm --cached .env        # stop tracking but keep file
git rm -r --cached dist/    # stop tracking directory

# Global gitignore (applies to all repos)
git config --global core.excludesfile ~/.gitignore_global