tech-studies

What is a branch?

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What is a branch?

A branch is a movable pointer to a commit — a 41-byte file under .git/refs/heads/, not a copy of your files.

Why it matters

Branches make parallel lines of work cheap, so they are the unit of nearly every workflow: feature work, hotfixes, release lines, and pull requests all live on branches. Because a branch is just a pointer, creating one is O(1) and uses no extra disk for the snapshot — this is why Git encourages many short-lived branches where older centralized tools (see centralized-vs-distributed-vcs) made branching expensive and rare.

How it works

Each commit records its parent(s), so the commit graph is a DAG. A branch name simply points at one commit — its tip — and history is everything reachable by walking parents backward.

        C---D   feature   (refs/heads/feature → D)
       /
A---B---E---F   main      (refs/heads/main → F)
                          HEAD → main
  • HEAD is a pointer to the current branch (ref: refs/heads/main), telling Git what the next commit’s parent is.
  • Committing moves the current branch tip forward by one and updates HEAD transitively.
  • A “detached HEAD” is HEAD pointing straight at a commit SHA instead of a branch name — new commits then belong to no branch and can be lost (see reflog-and-recovery-git-reflog).
ConceptWhat it isStorage
BranchPointer to a commit.git/refs/heads/<name> (one SHA)
HEADPointer to current branch.git/HEAD
CommitImmutable snapshot + parent linksobject database

Example

$ git rev-parse main
9f2c1ab...                      # the tip commit SHA
$ cat .git/refs/heads/main
9f2c1ab1d4e3...                 # the branch IS this line
$ git commit -m "x"            # main now points one commit further
$ cat .git/refs/heads/main
a71be09c5f8a...                 # same file, new SHA — no copy made

Pitfalls

  • Thinking a branch holds files — it holds one SHA. Deleting a branch (see deleting-branches) drops only the pointer; the commits survive until garbage-collected.
  • Committing on a detached HEAD — those commits are unreferenced; reattach with a branch or recover via reflog-and-recovery-git-reflog.
  • Confusing branch with tag — a tag is a fixed pointer; a branch moves as you commit.

See also

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