Checkout

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Checkout#

git checkout is a command that allows you to swich current state of project to the another commit.

Back up commit#

In the next example:

  • Two commits have been created:

    • first commit add first_file.

    • second commit edits first file and adds second file;

  • I used git log to show these commits:

    • Note the (HEAD->master) near second commit, this means you are staying on second commit and the master branch is pointing to it;

    • Note To print HEAD->master in jupyter notebook output you have to use the --decorate option for some reason, in terminal this is not necessary;

  • I stored the hash of the first commit in the first_hash variable and printed it;

  • Using git checkout $first_hash I moved HEAD to first commit, which means it’s now an active commit:

    • Note In real work you can use the hash of the commit and don’t use a variable to store the commit hash;

    • Note by default git checkout prints it’s message to the error stream, so I used 2>&1 to redirect it to the out stream;

  • By calling git log again, I showed:

    • That (HEAD) is now next to the first commit message;

    • The second commit isn’t even shown now - git’s default behaviour for git log is to show the history of the commit that created the head commit. Use the --all option to show all messages;

  • ls will show that there is no second file in the project folder now - it’s ok, we’ve moved to a commit where there is no such file;

  • cat first_file shows that the first file is still the same as it was in the second commit:

    • This is because we reverted git to first_commit but not the working directory. In git status you can see that first_file is marked as modified, it is indeed different from the commit that HEAD is currently referring to;

    • To return a file to the state as in first commit you simply need to do a git restore for that file, which is what I am doing and demonstrating the first_file from first commit.

%%bash
mkdir checkout_example
cd checkout_example

git init &> /dev/null

echo "some text" > first_file
git add first_file
git commit -m "first commit" &> /dev/null
first_hash=$(git rev-parse HEAD)

echo "some text" > second_file
echo "this is the text for second commit" > first_file
git add second_file
git commit -m "second commit" &> /dev/null

echo "=====log====="
git log --decorate

echo
echo "=====first commit hash====="
echo $first_hash

echo
echo "=====git chechout to first commit====="
git checkout $first_hash 2>&1

echo
echo "=====log====="
git log --decorate
echo "=====ls====="
ls
echo "=====first_file====="
cat first_file

echo
echo "====status====="
git status
git restore first_file
echo "=====first_file after restore====="
cat first_file


cd ..
rm -r checkout_example

=====log=====
commit 23e858c0a0924f75ef4f1a9eddf0c357f9d865b5 (HEAD -> master)
Author: Dranikf <kobfedsur@gmail.com>
Date:   Thu Sep 7 22:45:41 2023 +0300

    second commit

commit f42455672912f0347c9e29165583ddc5accf9b25
Author: Dranikf <kobfedsur@gmail.com>
Date:   Thu Sep 7 22:45:41 2023 +0300

    first commit

=====first commit hash=====
f42455672912f0347c9e29165583ddc5accf9b25

=====git chechout to first commit=====
Note: switching to 'f42455672912f0347c9e29165583ddc5accf9b25'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by switching back to a branch.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -c with the switch command. Example:

  git switch -c <new-branch-name>

Or undo this operation with:

  git switch -

Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at f424556 first commit
M	first_file

=====log=====
commit f42455672912f0347c9e29165583ddc5accf9b25 (HEAD)
Author: Dranikf <kobfedsur@gmail.com>
Date:   Thu Sep 7 22:45:41 2023 +0300

    first commit
=====ls=====
first_file
=====first_file=====
this is the text for second commit

====status=====
HEAD detached at f424556
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
	modified:   first_file

no changes added to commit (use "git add" and/or "git commit -a")
=====first_file after restore=====
some text
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