Blog

Git References, Commits, and Branches
Posted on August 30, 2020 in Git by Matt Jennings

References

They are pointers to commits.

Three Types of Git References

• Tags and Annotated Tags
• Branches
• HEAD

What is Head?

• HEAD is how git knows what branch you’re currently on, and what the next parent will be.
• It’s a pointer.
  • It usually points at the name of the current branch.
  • But, it can point at a commit too (detached HEAD).

Lightweight Tags (in practice not used much)

• Lightweight tags are just a simple pointer to a commit.
• When you create a tag with no arguments, it captures the value in HEAD.
• Example:
  git checkout master
git tag my-first-commit

Annotated Tags: git tag -a

• Point to a commit, but store additional information.
  • Author, message, date.
• Example:
  git tag -a v1.0 -m 'Version 1.0 of my blog'
git tag
git show v1.0

Tags and Branches

• Branch
  • The current branch pointer moves with every commit to the repository
• Tag
  • The commit that a tag points doesn’t change.
  • It’s a snapshot!

HEAD-less / Detached HEAD

• When I checked a checkout a specific commit or tag, I go into a detached HEAD state.
• git move the HEAD point to that commit.
• There is no reference pointing to the commits you made in a detached state.
• Save your work:
  • Create a new branch that points to the last commit you made in a detached state:
    git branch <new-branch-name> <commit>

Dangling Commits

• If you don’t point a new branch at those detached HEAD commits, they will not longer be referenced in git.
• Eventually they will be garbage collected.