Version Control with Git > 5. Exploring History > f. Exercises I

f. Exercises I

Recovering Older Versions of a File

Jennifer has made changes to the Python script that she has been working on for weeks, and the modifications she made this morning “broke” the script and it no longer runs. She has spent ~ 1hr trying to fix it, with no luck…

Luckily, she has been keeping track of her project’s versions using Git! Which commands below will let her recover the last committed version of her Python script called data_cruncher.py?

$ git checkout HEAD
$ git checkout HEAD data_cruncher.py
$ git checkout HEAD~1 data_cruncher.py
$ git checkout <unique ID of last commit data_cruncher.py
Both 2 and 4

Solution

Reverting a Commit

Jennifer is collaborating with colleagues on her Python script. She realizes her last commit to the project’s repository contained an error, and wants to undo it. Jennifer wants to undo correctly so everyone in the project’s repository gets the correct change. The command git revert [erroneous commit ID] will create a new commit that reverses the erroneous commit.

The command git revert is different from git checkout [commit ID] because git checkout returns the files not yet committed within the local repository to a previous state, whereas git revert reverses changes committed to the local and project repositories.

Below are the right steps and explanations for Jennifer to use git revert, what is the missing command?

________ # Look at the git history of the project to find the commit ID
Copy the ID (the first few characters of the ID, e.g. 0b1d055).
git revert [commit ID]
Type in the new commit message.
Save and close

Solution

Understanding Workflow and History

What is the output of the last command in

$ cd planets
$ echo "Venus is beautiful and full of love"  venus.txt
$ git add venus.txt
$ echo "Venus is too hot to be suitable as a base"  venus.txt
$ git commit -m "Comment on Venus as an unsuitable base"
$ git checkout HEAD venus.txt
$ cat venus.txt #this will print the contents of venus.txt to the screen

Venus is too hot to be suitable as a base

```
Venus is beautiful and full of love
```

Venus is beautiful and full of love
Venus is too hot to be suitable as a base

Error because you have changed venus.txt without committing the changes

Solution

The answer is 2.

The command git add venus.txt places the current version of venus.txt into the staging area. The changes to the file from the second echo command are only applied to the working copy, not the version in the staging area.

So, when git commit -m "Comment on Venus as an unsuitable base" is executed, the version of venus.txt committed to the repository is the one from the staging area and has only one line.

At this time, the working copy still has the second line (and git status will show that the file is modified). However, git checkout HEAD venus.txt replaces the working copy with the most recently committed version of venus.txt.

So, cat venus.txt will output

Venus is beautiful and full of love.