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.