Git checkout explained in detail [Practical Examples]

Git checkout switches between branches and undoes changes.

However, failure to deeply understand the command could prevent you from applying it correctly. Worse yet, you may not distinguish the checkout command from other git commands such as clone, restore, remove, reset, and revert.

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This tutorial simplifies deploying the checkout command. It explains the challenging parts of git checkout using relatable words and examples. Read on to learn more.

 

Git checkout command cheat sheet

Git checkout affects files, commits, and branches.

On files, git checkout undoes changes.

git checkout HEAD~N <file>

Alternatively, you can overwrite contents in the working tree to match the specified file in the index.

git checkout -f <pathspec>

Replacing the -f with the -p option

git checkout -p <pathspec>

shows the diff through an interactive interface.

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On commits, the command detaches the HEAD.

git checkout <SHA1>

Lastly, git checkout plays a massive role in branching. You can switch between existing branches,

git checkout <existing branch>

create a branch and move into it,

git checkout -b <new branch>

or navigate to a remote branch.

git checkout <remote branch>

Let us dive into git HEAD and branching.

 

A simple explanation of git HEAD and branch

You should understand how git stores snapshots of your changes before applying the checkout command.

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Initializing a repository creates a .git subdirectory in the filesystem. In git, a filesystem is a directory whose files and subdirectories you are modifying. A repository, on the other hand, is a collection of commits.

In technical terms, git is a version control system API for tracking objects and a naming system for the objects: refs.

Objects are blobs, trees, and commits. Commits reference trees, which in turn, reference blobs. Blobs contain file contents. Refs can be heads (branches) or tags.

A branch is a named reference to a commit. The last commit, also known as the repository tip or HEAD, gets tracked in the HEAD file. Switching between branches modifies the contents of the HEAD file.

Say the HEAD file's

cat .git/HEAD

content is ref: refs/heads/main. That means the tip of the latest commit lies in the main branch.

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Assume you then create the second branch and switch to it. The contents of the HEAD file

cat .git/HEAD

then become ref: refs/heads/second.

 

Where git checkout comes in a typical git workflow

Think of checkout as a compound word of check + out, which means "explore the contents of something."

Say you have committed to multiple branches and want to update the refs. Or you want to retreat your steps to a particular snapshot. Git checkout command comes in to help, depending on the supplied pathspec or option.

For example, during branching, the command automatically updates the HEAD file to notify git you are working on another branch.

Apart from the checkout command, you can use commands such as git rm, git restore, git reset, git revert, and git switch. Here is how to distinguish git checkout from the commands.

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How to distinguish the checkout command from other git commands

git rm works on committed changes, deleting files and directories from the file system

git rm <file or directory>

or unstaging them.

git rm --cached <file>

git restore with the --staged option does a similar job to git rm with the --cached option.

git restore --staged <file>

git reset exists in three forms: hard, soft, and mixed.

The hard reset

git reset --hard <HEAD or SHA1>

deletes the specified commits and the affected files from the file system.

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The soft reset

git reset --soft <HEAD or SHA1>

does not discard files but uncommits the changes.

Like git rm with the --cached option and git restore with the --staged option, the mixed reset

git reset HEAD

unstages changes.

It would be best to apply git reset on unpushed repositories and use git revert

git revert <HEAD or SHA1>

on a shared repository with a remote. Instead of discarding commits, git revert inverses them with a new commit. Unlike the reset or checkout commands, git revert only operates at the commit level.

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Another specific command is git clone.

git clone <remote URL>

git clone differs from git checkout because it fetches remote commits into the local repository, whereas the checkout command switches commit HEAD between local branches.

After checking out a branch, you can introduce more commits and combine them with the main branch by switching into the main branch and using git merge.

git merge <modified branch>

Here, you create a ball of commits and throw it into the main branch with a commit message. Use git rebase to stack the commits onto the main's changes.

git rebase <modified branch>

Commands such as git stash and cherry-pick help maintain a repository.

The key takeaway here is to use git checkout in switching branches and let other commands handle git unstaging. Besides, you can use supportive commands to ease collaboration and repository maintenance.

Enough with comparisons. Let us do some practice with the checkout command.

 

Lab setup to practice git checkout

I am creating a repository on GitHub called git_checkout.

Git checkout explained in detail [Practical Examples]

I then copy its URL and clone it on my terminal.

Git checkout explained in detail [Practical Examples]

cd into the cloned repository and create two files, stage, and commit them.

cd git_checkout
echo "File 1" > file1.txt
git add file1.txt
git commit -m "Track file 1"
echo "File 2" > file2.txt
git add file2.txt
git commit -m "Track file 2"
git push

We have three commits on the main branch.

git log

Git checkout explained in detail [Practical Examples]

Let us do some practice with the setup.

 

git checkout command examples

Example-1: Git checkout a file to undo commit using HEAD reference

We can undo the last commit by modifying file2.txt, staging, and committing it, then check it out.

echo "Modify file2.txt" >> file2.txt
git add .
git commit -m "Change file 2"

Check status,

git status

undo the last commit,

git checkout HEAD~1 file2.txt

and recheck the status.

git status

The changes returned to the index.

Git checkout explained in detail [Practical Examples]

 

Example-2: Git undo a specific commit using checkout

Let us log history and check out the second commit from the local HEAD.

git log --pretty=oneline
git checkout 0cff5e7c8263a11b405ed8d3735d6257fdeeb055
​

Git tells us we are in a detached HEAD. That means the ref in the .git/HEAD file does not match a branch, as git expects it to.

Git sees ref: refs/heads/<commit> instead of the expected format ref: refs/heads/<branch>. So, git does not know what to do with changes you do at the misplaced HEAD.

The best time to check out a commit is when restoring commits after a hard reset. Let us return the HEAD to the main branch.

git checkout main

Reset the last commit.

git reset --hard HEAD^

And restore it from the reflog using the checkout command and a new branch.

git reflog
git checkout 0cff5e7
git switch -c new_branch

Return to the main branch and rebase the new_branch.

git checkout main
git rebase new_branch

Rechecking the history

git log --pretty=oneline

confirms the restored changes.

Git checkout explained in detail [Practical Examples]

 

Example-3: Checkout and switch to an existing branch

Let us switch to the new_branch branch, add a commit, and push it with its changes to the remote.

git checkout new_branch
echo "File 3" > file3.txt
git add file3.txt
git commit -m "Add file 3, second branch"
git push origin new_branch

git checkout an existing branch

You can then create a pull request on GitHub to merge the branches remotely.

 

Example-4: Checkout and create a new branch

Apart from switching to an existing branch and making changes, you can create a new branch using the checkout command and the -b option.

git checkout -b third_branch

Checking the number of branches

git branch

confirms we have three branches: main, new_branch, and third_branch.

Git checkout explained in detail [Practical Examples]

 

Example-5: Checkout and switch into a remote branch

Let us list all the remote branches using the -r option.

git branch -r

And switch to the origin/new_branch branch by checking it out.

git checkout origin/new_branch

That detaches the HEAD. We can then create a branch from the detached HEAD as we did in example~2 above.

Git checkout explained in detail [Practical Examples]

 

Conclusion

Git checkout is a multi-purpose command. It allows you to undo changes and switch the HEAD between branches. Using it effectively requires understanding the origin of the term HEAD and distinguishing the command from related commands, as explained in this tutorial.

 

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