Time Travel in Git with Detached HEAD

Imagine your supervisor tells you:
"This feature was working yesterday but is broken today — you must have caused it!"

How do you prove whether it was really your change or the bug was already there?

This is where Git time travel comes in handy. You can move to a specific commit from the past, see exactly what the code looked like, and even compare it with your current version. Let’s see how.

Scenario Setup

Create a new project:

mkdir project8
cd project8
git init

Make a file and commit it:

echo "line added in first commit" > feature.txt
git add feature.txt
git commit -m "First commit"

Add two more commits:

echo "line added in second commit" >> feature.txt
git commit -am "Second commit"

echo "line added in third commit" >> feature.txt
git commit -am "Third commit"

Check history:

git log --oneline

Output:

c3e4f3c Third commit
9a7b1d2 Second commit
4b1c2a1 First commit

Switching to an Old Commit

Normally, git switch <branch> works for branches. But here we want to move to a specific commit.

git switch --detach 9a7b1d2

Now Git prints:

HEAD is now at 9a7b1d2 Second commit

Open the file:

cat feature.txt
# line added in first commit
# line added in second commit

You’ve successfully traveled back in time 🚀.

Visual Representation





Using Git Checkout (Old Way)


The same can also be done with git checkout:


git checkout 4b1c2a1



Output:


Note: switching to '4b1c2a1'.
You are in 'detached HEAD' state...



It’s the same as git switch --detach.




Warning About Detached HEAD


When you are in a detached HEAD state:


    

  • You are not on a branch.
    • 

  • If you make new commits here, they are not referenced by any branch.
    • 

  • Git’s garbage collector may eventually remove them.
    • 



For example:


echo "temp change" > temp.txt
git add temp.txt
git commit -m "Temporary commit"



If you now switch back to main:


git switch main



That temporary commit is left dangling. It may be garbage-collected later.




🔑 Rule of Thumb: Avoid committing in detached HEAD unless you plan to create a new branch from there.






Practical Use Case


    

  • Reproduce an old version of the project exactly as it was.
    • 

  • Prove whether a bug existed in earlier commits.
    • 

  • Compare file changes between two points in time.
    • 





Summary


    

  • Use git switch --detach <commit-id> or git checkout <commit-id> to view old commits.
    • 

  • This is called detached HEAD state.
    • 

  • Never commit in detached HEAD unless you create a new branch to save your work.
    • 

  • Perfect for time travel in Git to debug or verify past code.
    • 





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