Git checkout

This page is an examination of thegit checkout command. It will cover usage examples and edge cases. In Git terms, a "checkout" is the act of switching between different versions of a target entity. Thegit checkout command operates upon three distinct entities: files, commits, and branches. In addition to the definition of "checkout" the phrase "checking out" is commonly used to imply the act of executing thegit checkout command. In theUndoing Changes topic, we saw howgit checkout can be used to view old commits. The focus for the majority of this document will be checkout operations on branches.

Checking out branches is similar to checking out old commits and files in that the working directory is updated to match the selected branch/revision; however, new changes are saved in the project history—that is, it’s not a read-only operation.

Checking out branches

Thegit checkout command lets you navigate between the branches created bygit branch. Checking out a branch updates the files in the working directory to match the version stored in that branch, and it tells Git to record all new commits on that branch. Think of it as a way to select which line of development you’re working on.

Having a dedicated branch for each new feature is a dramatic shift from a traditional SVN workflow. It makes it ridiculously easy to try new experiments without the fear of destroying existing functionality, and it makes it possible to work on many unrelated features at the same time. In addition, branches also facilitate several collaborative workflows.

Thegit checkout command may occasionally be confused withgit clone. The difference between the two commands is that clone works to fetch code from a remote repository, alternatively checkout works to switch between versions of code already on the local system.

Usage: Existing branches

Assuming the repo you're working in contains pre-existing branches, you can switch between these branches usinggit checkout. To find out what branches are available and what the current branch name is, executegit branch.

$＞ git branch 
main 
another_branch 
feature_inprogress_branch 
$＞ git checkout feature_inprogress_branch

The above example demonstrates how to view a list of available branches by executing thegit branch command, and switch to a specified branch, in this case, thefeature_inprogress_branch.

New branches

Git checkout works hand-in-hand withgit branch. Thegit branch command can be used to create a new branch. When you want to start a new feature, you create a new branch offmain usinggit branch new_branch. Once created you can then usegit checkout new_branch to switch to that branch. Additionally, Thegit checkout command accepts a-b argument that acts as a convenience method which will create the new branch and immediately switch to it. You can work on multiple features in a single repository by switching between them withgit checkout.

git checkout -b ＜new-branch＞

The above example simultaneously creates and checks out＜new-branch＞. The-b option is a convenience flag that tells Git to rungit branch before runninggit checkout ＜new-branch＞.

git checkout -b ＜new-branch＞ ＜existing-branch＞

By defaultgit checkout -b will base thenew-branch off the currentHEAD. An optional additional branch parameter can be passed togit checkout. In the above example,＜existing-branch＞ is passed which then basesnew-branch off ofexisting-branch instead of the currentHEAD.

Switching branches

Switching branches is a straightforward operation. Executing the following will pointHEAD to the tip of＜branchname＞.

git checkout ＜branchname＞

Git tracks a history of checkout operations in the reflog. You can executegit reflog to view the history.

Git checkout a remote branch

When collaborating with a team it is common to utilize remote repositories. These repositories may be hosted and shared or they may be another colleague's local copy. Each remote repository will contain its own set of branches. In order to checkout a remote branch you have to first fetch the contents of the branch.

git fetch --all

In modern versions of Git, you can then checkout the remote branch like a local branch.

git checkout ＜remotebranch＞

Older versions of Git require the creation of a new branch based on theremote.

git checkout -b ＜remotebranch＞ origin/＜remotebranch＞

Additionally you can checkout a new local branch and reset it to the remote branches last commit.

git checkout -b ＜branchname＞
git reset --hard origin/＜branchname＞

Detached HEADS

Now that we’ve seen the three main uses ofgit checkout on branches, it's important to discuss the“detached HEAD” state. Remember that theHEAD is Git’s way of referring to the current snapshot. Internally, thegit checkout command simply updates theHEAD to point to either the specified branch or commit. When it points to a branch, Git doesn't complain, but when you check out a commit, it switches into a“detached HEAD” state.

This is a warning telling you that everything you’re doing is “detached” from the rest of your project’s development. If you were to start developing a feature while in a detachedHEAD state, there would be no branch allowing you to get back to it. When you inevitably check out another branch (e.g., to merge your feature in), there would be no way to reference your feature:

The point is, your development should always take place on a branch—never on a detachedHEAD. This makes sure you always have a reference to your new commits. However, if you’re just looking at an old commit, it doesn’t really matter if you’re in a detachedHEAD state or not.

Summary

This page focused on usage of thegit checkout command when changing branches. In summation,git checkout, when used on branches, alters the target of theHEAD ref. It can be used to create branches, switch branches, and checkout remote branches. Thegit checkout command is an essential tool for standard Git operation. It is a counterpart togit merge. Thegit checkout andgit merge commands are critical tools to enablinggit workflows.

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