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git merge

Description:
Integrate changes from one branch into another. Combines the history of two branches into one.

Syntax:

git merge <branch-name>
git merge --no-ff <branch-name>
git merge --squash <branch-name>

Examples:

# Merge feature branch into current branch
git merge feature/login

# Merge with a merge commit (no fast-forward)
git merge --no-ff feature/payment

# Squash all commits into one before merging
git merge --squash feature/ui-updates

# Abort a merge in progress
git merge --abort

# Continue merge after resolving conflicts
git merge --continue

Detailed Explanation:

• Two merge types: Fast-forward (linear history) or three-way merge (creates merge commit)
• Fast-forward: If no divergent changes, just moves branch pointer forward
• Merge commit: If branches diverged, creates a new commit with two parents
• Conflict resolution: If same lines changed in both branches, manual resolution is required

Common Errors:

• CONFLICT (content): Merge conflict in <file> → Solution: Open file, resolve conflicts, git add, then git commit
• error: You have not concluded your merge → Solution: Finish current merge with git commit or abort with git merge --abort
• fatal: refusing to merge unrelated histories → Solution: Add --allow-unrelated-histories flag (rare cases only)

Pro Tips:

• Always commit or stash changes before merging
• Use --no-ff to preserve feature branch history (creates merge commit even if fast-forward possible)
• Use --squash to clean up many small commits before merging into main branch
• Preview merge before doing it: git log ..feature-branch
• Use git mergetool to resolve conflicts with visual tools
• Warning: Test thoroughly after merge; conflicts might break functionality

Related Commands:

• git rebase – Alternative way to integrate changes (linear history)
• git cherry-pick – Apply specific commits from another branch
• git diff – Compare branches before merging
• git log – View branch history

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Quick Reference

Command	Description
git branch	List branches
git branch <name>	Create new branch
git branch -d <name>	Delete merged branch
git checkout <branch>	Switch to branch (old way)
git switch <branch>	Switch to branch (new way)
git switch -c <name>	Create and switch to new branch
git merge <branch>	Merge branch into current

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Branch Workflow Example

# Start a new feature
git switch -c feature/user-auth

# Work on the feature (make changes, commit)
git add .
git commit -m "Add login form"

# Switch back to main branch
git switch main

# Merge the feature
git merge feature/user-auth

# Delete the feature branch (optional)
git branch -d feature/user-auth

# Push changes to remote
git push origin main

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