In TortoiseGit, which one is MERGE_HEAD and which one is HEAD?

In TortoiseGit, which one is MERGE_HEAD and which one is HEAD?

They are both local (this is important, albeit not very helpful :-) ).

HEAD is your current branch, which means the one you have checked out now. For git merge that's the one you had checked out when you started.

MERGE_HEAD is the other commit, which means the hash ID of the commit you told Git to merge. That is, git merge origin/master resolves origin/master to some local commit hash ID, and then merges that commit, and MERGE_HEAD contains the hash ID of that commit.

I think a better term for the other commit is other or --theirs, and Git sometimes uses those terms, but other bits of Git do use the term remote to refer to the --theirs commit.

 

MERGE_HEAD  vs HEAD in Git

In Git, HEAD is a pointer to the current branch, which points to the most recent commit in that branch. The HEAD pointer is updated automatically when new commits are made to the current branch.

MERGE_HEAD is a pointer to the most recent commit in the branch that was merged into the current branch during a merge operation. When you perform a merge in Git, the MERGE_HEAD pointer is updated to point to the most recent commit in the merged branch.

So, while HEAD points to the most recent commit in the current branch, MERGE_HEAD points to the most recent commit in the branch that was just merged into the current branch.

It's worth noting that MERGE_HEAD is a temporary pointer that is only valid during a merge operation, and it is reset after the merge is complete. On the other hand, HEAD is a long-lived pointer that is always present in a Git repository.

 

What's the merged branch you mentioned above? demonstrate the concept with an sample

In Git, merging refers to combining changes from one branch into another branch. When you merge one branch into another branch, Git creates a new commit that incorporates the changes from both branches.

Let's say we have two branches: master and feature-branch. Initially, both branches point to the same commit in the Git history:

css

A (master, feature-branch)

Then, we make some changes on the feature-branch:

 

A (master)
 \
  B (feature-branch)

Now, if we want to incorporate the changes from feature-branch into master, we can merge feature-branch into master:

A ---- C (master)
 \    /
  B (feature-branch)

In this example, C is the new commit that results from the merge. It contains the changes from both A and B.

After the merge, Git updates the HEAD reference to point to the new commit C, which is the latest commit on the master branch. This means that HEAD now refers to C.

MERGE_HEAD, on the other hand, is a reference that Git creates during the merge operation. It points to the latest commit on the branch that was merged into the current branch. In the example above, after the merge, MERGE_HEAD would point to commit B, which is the latest commit on feature-branch.

MERGE_HEAD is used by Git to keep track of the merge operation. It allows Git to create a new commit that incorporates the changes from both branches, and to update the branch pointers to point to the new commit.

Note that MERGE_HEAD is a temporary reference that is created during the merge operation and is deleted once the merge is complete.

 

作者:Chuck Lu    GitHub