{"id":"l-git-2-1","courseId":"git-github","lang":"en","kind":"lesson","summary":"Create, switch, rename and delete branches knowing that each is a movable pointer to a commit, and recover cleanly from a detached HEAD.","html":"

In older version control systems a branch was a full copy of the project, slow to make and painful to combine, so people avoided them. In Git a branch costs almost nothing. That changes how you work: every idea, fix or experiment on your portfolio can get its own branch, and throwing one away is as cheap as making it.

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A branch is a sticky note

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Look inside your repository:

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Terminal
cat .git/refs/heads/main
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Text
c39be1142d6f0a8e7b1c5d93e2f4a0b6c8d7e912
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That’s the whole main branch: a file containing one commit ID. A branch is a named, movable pointer to a commit. The history behind it isn’t stored in the branch; it’s found by following parent links from that commit, as you did in the last lesson.

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So how does Git know which branch you’re on? Another small file:

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Terminal
cat .git/HEAD
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Text
ref: refs/heads/main
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HEAD is a pointer to a pointer. It normally names a branch, and that branch names a commit. When you commit, Git creates the new commit with the current one as its parent, then moves the branch HEAD names to the new commit. HEAD itself doesn’t change; it’s still “on main”, and main has moved forward.

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You don’t need to read these files day to day (in older or busier repositories, branch IDs may be packed into .git/packed-refs instead), but seeing them once removes the mystery. Everything in this section is about moving these sticky notes around a graph.

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Making and moving between branches

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Your next portfolio change is a site footer. Give it a branch:

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Terminal
git switch -c footer
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Text
Switched to a new branch 'footer'
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-c creates the branch at your current commit and switches to it. The two-step version is git branch footer followed by git switch footer. Now commit some work:

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Terminal
git add index.html styles.css\ngit commit -m \"Add site footer with contact links\"
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\n Before: commits a1c9, b2e0, c39b in a row; main and footer both point at c39b; HEAD points at footer. After committing: a new commit f1a3 follows c39b; footer and HEAD moved to f1a3; main stayed on c39b.\n Before\n \n a1c9\n \n b2e0\n \n c39b\n \n \n \n main\n \n footer\n \n HEAD\n \n After git commit\n \n a1c9\n \n b2e0\n \n c39b\n \n f1a3\n \n \n \n \n main\n \n \n footer\n \n HEAD\n \n
Committing moves the branch that HEAD is attached to
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main is untouched. Switch back and the footer disappears from your files; switch to footer again and it returns:

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Terminal
git switch main      # working tree now matches main's snapshot\ngit switch footer    # and now footer's\ngit switch -         # back to whichever branch you were on before
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Switching rewrites the files in your working tree to match the target snapshot. Uncommitted changes come along if they don’t clash with the target. If they would be overwritten, Git refuses to switch and tells you to commit or stash first. That refusal is protecting you; don’t look for a way around it. Commit the work, or wait for the stash lesson in section 4.

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Housekeeping

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Terminal
git branch                 # list local branches; * marks the current one\ngit branch -v              # with the commit each points to\ngit branch -m footer site-footer   # rename\ngit branch -d site-footer  # delete, only if its work is merged\ngit branch -D experiment   # force-delete, merged or not
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-d refuses to delete a branch whose commits aren’t merged into your current branch (or into the branch’s upstream, once it has one), which is a useful safety net. -D skips the check. Use it only when you’re sure the work is unwanted.

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Name branches for what they do: footer, fix-mobile-nav, projects-grid. Many teams add a prefix such as feat/ or fix/; slashes are allowed in branch names.

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Borrowing one file from another branch

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Sometimes you want one file from another branch without the rest of its work. git restore can read from any commit:

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Terminal
git restore --source=dark-mode styles.css
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That overwrites styles.css in your working tree with the version on dark-mode. Check it with git diff, then stage and commit it on your current branch. You’ll still see older tutorials use git checkout for both switching and restoring; Git 2.23 split those two jobs into git switch and git restore, which are harder to confuse.

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Detached HEAD

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You can point HEAD straight at a commit instead of a branch, to look at an old version of the site:

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Terminal
git switch --detach a1c9d72
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Git warns you’re in detached HEAD state. Looking around is perfectly safe. The risk is committing there: new commits belong to no branch, so when you switch away, nothing points at them and they quietly drop out of git log.

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Your footer branch is ready and main hasn’t moved. Next you’ll bring the two together with a merge.

\n","toc":[{"id":"sec-1","text":"A branch is a sticky note","level":2},{"id":"sec-2","text":"Making and moving between branches","level":2},{"id":"sec-3","text":"Housekeeping","level":2},{"id":"sec-4","text":"Borrowing one file from another branch","level":2},{"id":"sec-5","text":"Detached HEAD","level":2}],"takeaways":["A branch is a tiny file holding one commit ID; creating one copies nothing and takes milliseconds.","HEAD names the branch you’re on, and each new commit moves that branch forward while HEAD comes along.","git switch -c <name> creates a branch at the current commit and switches to it in one step.","A detached HEAD points straight at a commit; save any work made there with git switch -c <name> before leaving.","git restore --source=<branch> <file> copies one file from another branch without switching to it."],"further":[{"title":"Branches in a Nutshell (Pro Git)","url":"https://git-scm.com/book/en/v2/Git-Branching-Branches-in-a-Nutshell"},{"title":"git switch reference","url":"https://git-scm.com/docs/git-switch"},{"title":"git branch reference","url":"https://git-scm.com/docs/git-branch"}],"quiz":[{"q":"

You’re on main at commit b2e0 and run git switch -c footer, then commit f1a3. Where do main and footer point now?

","options":[{"text":"Both point at f1a3, because they were created from the same commit.","why":"Branches don’t stay linked. Only the branch HEAD is attached to moves when you commit."},{"text":"main points at f1a3 and footer at b2e0.","why":"That’s reversed. You switched to footer, so footer is the one that moves."},{"text":"Neither moved; branches only move when you push.","why":"Committing moves the current branch immediately. Pushing is about copying commits to a remote."},{"text":"main still points at b2e0; footer moved to f1a3.","why":"Correct. HEAD was attached to footer, so the new commit advanced footer and left main where it was."}],"answer":3},{"q":"

What does the file .git/HEAD contain while you’re on the footer branch?

","options":[{"text":"ref: refs/heads/footer","why":"Correct. HEAD normally holds the name of a branch, not a commit ID. That indirection is what lets commits move the branch."},{"text":"The 40-character ID of the latest commit on footer.","why":"That’s what the branch file .git/refs/heads/footer holds. HEAD points at the branch, and the branch points at the commit."},{"text":"A list of every branch in the repository.","why":"git branch builds that list by reading the branch files. HEAD stores only where you are."}],"answer":0},{"q":"

You checked out an old commit to look around, made a quick fix and committed it. Git says you’re in “detached HEAD” state. How do you keep that commit?

","options":[{"text":"Run git switch main; the commit comes with you.","why":"Switching away leaves the commit behind with no branch pointing at it. It becomes easy to lose and is eventually garbage-collected."},{"text":"Nothing to do; every commit is kept on main automatically.","why":"In detached HEAD, new commits belong to no branch at all, which is exactly the risk."},{"text":"Run git switch -c old-fix to put a branch on it.","why":"Correct. A branch pointing at the commit makes it reachable, so it’s safe. You can merge it later."},{"text":"Run git commit --attach.","why":"There’s no --attach option. Attaching work to history means creating a branch at it."}],"answer":2},{"q":"

Your dark-mode branch has a finished styles.css you want on footer too, without merging the rest of dark-mode. You’re on footer. Which command does it?

","options":[{"text":"git switch dark-mode styles.css","why":"git switch changes branches. It doesn’t take file paths."},{"text":"git restore --source=dark-mode styles.css","why":"Correct. It writes styles.css from the dark-mode snapshot into your working tree; then you review, stage and commit it on footer."},{"text":"git branch dark-mode styles.css","why":"That form tries to create a branch named dark-mode starting at a commit called styles.css, which fails."},{"text":"git merge dark-mode -- styles.css","why":"Merges always combine whole commits. There’s no way to merge a single file."}],"answer":1}],"exercise":{"kind":"fill","language":"bash","template":"git switch {{0}} footer # create the branch and move onto it\ngit add index.html styles.css\ngit commit -m \"Add site footer with contact links\"\ngit switch {{1}} # back to main to check it's untouched\ngit branch -m footer {{2}} # rename to site-footer","blanks":[{"answers":["-c","--create"]},{"answers":["main","-"]},{"answers":["site-footer"]}],"title":"Branch for the footer","prompt":"

Fill in the blanks: create a footer branch and switch to it in one command, commit the footer, go back to main to confirm it hasn’t changed, then rename the branch to site-footer.

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git switch -c footer creates footer at the current commit and attaches HEAD to it, so the commit moves footer and leaves main alone. git switch main (or git switch -, which means the previous branch) rewrites the working tree to main’s snapshot. git branch -m footer site-footer renames the pointer; the commits don’t change at all.

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