Git Immersion

lab 11 Getting Old Versions

Goals

Going back in history is very easy. The checkout command will copy any snapshot from the repository to the working directory.

Get the hashes for previous versions

Execute:

git hist

Note: You did remember to define hist in your .gitconfig file, right? If not, review the lab on aliases.

Output:

$ git hist
* 1c410c6 2023-08-21 | Add a comment (HEAD -> main) [Théophile Chevalier]
* 0bf384c 2023-08-21 | Display user input [Théophile Chevalier]
* 31c3945 2023-08-21 | Add some content [Théophile Chevalier]
* aa5d425 2023-08-21 | First Commit [Théophile Chevalier]

Examine the log output and find the hash for the first commit. It should be the last line of the git hist output. Use that hash code (the first 7 characters are enough) in the command below. Then check the contents of the hello.py file.

Execute:

git checkout <hash>
cat hello.py

Note: The commands given here are Unix commands and work on both Mac and Linux boxes. Unfortunately, Windows users will have to translate to their native commands => That’s why we installed gitbash

Note: Many commands depend on the hash values in the repository. Since your hash values will vary from mine, whenever you see something like <hash> or <treehash> in the command, substitute in the proper hash value for your repository.

You should see …

Output:

$ git checkout aa5d425
Note: switching to 'aa5d425'.

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 aa5d425 First Commit
$ cat hello.py
print("Hello, World")

The output of the checkout command explains the situation pretty well. Older versions of git will complain about not being on a local branch. In any case, don’t worry about that for now.

Notice the contents of the hello.py file are the original contents.

Return the latest version in the main branch

Execute:

git checkout main
cat hello.py

You should see …

Output:

$ git checkout main
Previous HEAD position was aa5d425 First Commit
Switched to branch 'main'
$ cat hello.py
import sys

# Display user input
print(f"Hello, World! With user input : {sys.argv[0]}")

‘main’ is the name of the default branch. By checking out a branch by name, you go to the latest version of that branch.