Checkout Branch

In Git, to "checkout" from a branch means to switch your working directory to that branch, making it the active branch. This updates your files to match the state of that branch and allows you to work on it.

Switching

git switch main
git checkout main          # the older equivalent

Git rewrites the files in your working directory to match the target branch, and HEAD — the label for "where you are" — moves to point at it. Your commits stay where they are; only the pointer moves.

Uncommitted changes come with you

If you have edits that do not conflict with the branch you are moving to, Git carries them across. If a file differs between the two branches and you have edited it, Git refuses to switch rather than overwrite your work, which is the behaviour you want.

git stash        # put the changes away
git switch main
git stash pop    # and bring them back

Starting a branch that does not exist yet

git switch -c new-branch
git checkout -b new-branch

This creates and switches in one step. See Creating Branch.

One file from another branch

To take a single file from somewhere else without switching branches:

git restore --source=main -- src/index.ts

That copies the version from main into your working directory, leaving your current branch checked out. Useful for pulling in a fix someone else made without pulling in everything else they did.

Detached HEAD

Checking out a commit hash rather than a branch name leaves you in a "detached HEAD" state: HEAD points straight at a commit, with no branch name attached. It is a normal state to be in, and the only real risk is committing to it by accident, since a new commit there belongs to no branch. Create a branch for it with git switch -c saved if you want to keep the work.

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