git merge command - Step-by-Step Execution

Process Flow - git merge command

Start on branch A

↓

Check for changes in branch B

↓

Merge branch B into A

↓

Check for conflicts?

Yes→Resolve conflicts

↓

Commit merge

↓

Fast-forward or create merge commit

↓

Merge complete, branch A updated

The git merge command combines changes from one branch into another, checking for conflicts and either fast-forwarding or creating a merge commit.

Execution Sample

Git

git checkout main
git merge feature

Switch to main branch and merge changes from feature branch into main.

Process Table

Step	Action	Branch	Conflict Detected	Result
1	Checkout main branch	main	No	Switched to main
2	Start merge feature into main	main + feature	No	Fast-forward merge applied
3	Update main branch pointer	main	No	main now includes feature changes
4	Merge complete	main	No	No conflicts, merge successful

💡 Merge finished successfully with no conflicts; main branch updated to include feature branch changes.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
HEAD (current branch)	main	main	main	main	main
main branch commit	commitA	commitA	commitB	commitB	commitB
feature branch commit	commitB	commitB	commitB	commitB	commitB
Merge conflict	none	none	none	none	none

Key Moments - 2 Insights

Why does git sometimes create a merge commit and other times fast-forward?

If the current branch has no new commits since branching, git fast-forwards (see Step 2). Otherwise, it creates a merge commit to combine histories.

What happens if there is a conflict during merge?

Git pauses the merge and marks conflicts for manual resolution (not shown here because no conflicts occurred). After resolving, you commit the merge.

Visual Quiz - 3 Questions

Look at the execution table, what is the state of the main branch after Step 3?

A It is detached from any commit

B It points to the same commit as feature branch

C It points to an older commit than before

D It has conflicts to resolve

💡 Hint

Check the 'main branch commit' variable in variable_tracker after Step 3

At which step does git check for conflicts during the merge?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the 'Conflict Detected' column in execution_table

If the main branch had new commits after branching, how would the merge result change?

A Git would delete the feature branch

B Git would fast-forward the main branch

C Git would create a merge commit

D Git would abort the merge automatically

💡 Hint

Refer to key_moments explanation about merge commit vs fast-forward

Concept Snapshot

git merge command:
- Combines changes from one branch into current branch
- If no new commits on current branch, fast-forward happens
- Otherwise, creates a merge commit
- Conflicts must be resolved manually
- Use 'git merge branch_name' to merge

Full Transcript

The git merge command is used to combine changes from one branch into another. First, you switch to the branch you want to update, for example, main. Then you run 'git merge feature' to bring changes from the feature branch into main. Git checks if the main branch has new commits since branching. If not, it fast-forwards main to the feature commit. If there are new commits, git creates a merge commit to combine histories. If conflicts occur, git stops and asks you to resolve them manually before completing the merge. This process updates the current branch with changes from the other branch.

Practice

1. What does the git merge command do in Git?

easy

A. It combines changes from one branch into the current branch.

B. It deletes a branch permanently.

C. It creates a new branch from the current branch.

D. It shows the commit history of the current branch.

Solution

1. Step 1: Understand the purpose of git merge

   The git merge command is used to combine changes from one branch into another branch.

2. Step 2: Identify the correct description

   Among the options, only It combines changes from one branch into the current branch. correctly describes merging changes into the current branch.

3. Final Answer:

   It combines changes from one branch into the current branch. -> Option A

4. Quick Check:

   git merge = combine branches [OK]

Hint: Merge means combine changes into current branch [OK]

Common Mistakes:

• Confusing merge with branch deletion
• Thinking merge creates a new branch
• Mixing merge with viewing history

2. Which of the following is the correct syntax to merge branch feature into the current branch?

easy

A. git merge --create feature

B. git merge -b feature

C. git merge feature

D. git merge --delete feature

Solution

1. Step 1: Recall the basic merge syntax

   The correct syntax to merge a branch is git merge branch_name.

2. Step 2: Match the syntax with options

   git merge feature matches the correct syntax. Options B, C, and D use invalid flags or commands.

3. Final Answer:

   git merge feature -> Option C

4. Quick Check:

   git merge + branch name = correct syntax [OK]

Hint: Use 'git merge branch_name' to merge branches [OK]

Common Mistakes:

• Adding incorrect flags like -b or --create
• Confusing merge with branch creation or deletion
• Using merge without specifying branch name

3. Given the following commands run in order:

git checkout main
git merge feature

What happens if the feature branch has commits not in main?

medium

A. The main branch is reset to feature branch state.

B. The feature branch is deleted automatically.

C. Git throws an error and stops the merge.

D. The commits from feature are added to main.

Solution

1. Step 1: Understand merge behavior with new commits

   When merging a branch with new commits, Git combines those commits into the current branch.

2. Step 2: Analyze the options

   The commits from feature are added to main correctly describes this behavior. Options B, C, and D describe incorrect or unrelated behaviors.

3. Final Answer:

   The commits from feature are added to main. -> Option D

4. Quick Check:

   Merge adds commits [OK]

Hint: Merge adds commits, does not delete branches [OK]

Common Mistakes:

• Thinking merge deletes branches
• Expecting merge to reset branches
• Assuming merge always fails with new commits

4. You run git merge feature but Git reports a conflict. What should you do next?

medium

A. Restart Git to clear the conflict.

B. Manually resolve the conflicts in files, then run git add and git commit.

C. Run git merge --force to ignore conflicts.

D. Delete the feature branch and try merging again.

Solution

1. Step 1: Understand merge conflicts

   When Git reports conflicts, it means changes clash and need manual fixing.

2. Step 2: Resolve conflicts properly

   You must edit conflicted files to fix issues, then stage and commit the changes to complete the merge.

3. Final Answer:

   Manually resolve the conflicts in files, then run git add and git commit. -> Option B

4. Quick Check:

   Fix conflicts manually, then add and commit [OK]

Hint: Fix conflicts manually, then add and commit [OK]

Common Mistakes:

• Trying to force merge ignoring conflicts
• Deleting branches to fix conflicts
• Restarting Git expecting conflicts to clear

5. You want to merge branch feature into main but keep main's changes in case of conflict (favor main). Which command helps achieve this?

hard

A. git merge -X ours feature

B. git merge --no-ff feature

C. git merge -s recursive feature

D. git merge --abort feature

Solution

1. Step 1: Understand merge strategies

   The -X ours option tells Git to favor the current branch's changes during conflicts.

2. Step 2: Match the option to the goal

   git merge -X ours feature uses -X ours to keep main's changes if conflicts occur. Other options do not achieve this.

3. Final Answer:

   git merge -X ours feature -> Option A

4. Quick Check:

   Use -X ours to favor current branch on conflicts [OK]

Hint: Use 'git merge -X ours' to keep current branch changes [OK]

Common Mistakes:

• Confusing -X ours with --no-ff
• Using --abort to fix conflicts
• Not specifying strategy option