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Exercise - Use Git to fix mistakes

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Now, let's get some hands-on practice fixing our mistakes!

Practice recovering a deleted file

1. First, try deleting index.html:

   rm index.html
   

   It might seem like a bad idea, but remember: Git has your back!

2. Use an ls command to verify that index.html was deleted:

   ls
   

3. You should see the following output. Note that now, there's no index.html file!

   CSS
   

4. Let's recover index.html. Use git checkout to bring back index.html:

   git checkout -- index.html
   

5. Use ls again to check the contents of the current directory. Has index.html been restored?

   Yes! Now, the output should have an index.html file and a CSS directory:

   CSS  index.html
   

Practice recovering a file that was deleted: git rm

When you want to recover deleted files, things are a little more complicated if you delete them by using git rm instead of by using rm.

1. To see what happens, try this command:

   git rm index.html
   

2. Again, look for index.html by running ls. You should not see index.html.

3. Try to recover index.html the same way that you did last time:

   git checkout -- index.html
   

4. This time, Git complains that it knows nothing about index.html. That's because Git not only deleted the file, it recorded the deletion in the index:

   error: pathspec 'index.html' did not match any file(s) known to git.
   

5. Unstage the deletion of index.html with the git reset command:

   git reset HEAD index.html
   

6. Check for this output, which confirms it:

   Unstaged changes after reset:
   D       index.html
   

7. Now, you can recover your file from the index with the command you used before:

   git checkout -- index.html
   

   git reset unstaged the change, but the file was still deleted, so you had to use checkout to get it back.

8. Double-check that it worked by running ls.

Revert a commit

Now, let's make things more complicated. Suppose you accidentally overwrite one file with another file, or you make a change to a file that turns out to be a big mistake. You want to revert to the previous version of the file, but you had already committed the changes. In this case, a simple git checkout won't do the trick.

One solution to this problem is to revert the previous commit.

1. Open index.html with code:

   code index.html
   

2. Replace the contents of index.html with this code:

   <h1>That was a mistake!</h1>
   

3. Save and close the file.

4. Use these commands to commit the changes, and show the latest commit:

   git commit -m "Purposely overwrite the contents of index.html" index.html
   git log -n1
   

   The -n1 flag here tells Git that we want only the most recent commit entry.

5. Use the following commands to attempt to restore index.html:

   git checkout -- index.html
   

6. Open index.html in the editor:

   code index.html
   

   Which version of index.html do you see? The old version or the new version?

   In this situation, the best course of action is to revert the change by making another commit that cancels out the first one. That's a job for git revert.

7. Close the file and use git revert to undo your committed changes:

   git revert --no-edit HEAD
   

   The --no-edit flag tells Git that we don't want to add a commit message for this action.

8. Check the output. It should look similar to this example:

   [main 6a27310] Revert "Purposely overwrite the contents of index.html"
   1 file changed, 13 insertions(+), 1 deletion(-)
   

9. Follow up with a git log command to show the latest commit:

   git log -n1
   

10. Check the output again. It should look like this example:

    Author: User Name <user-name@contoso.com>
    Date:   Tue Nov 19 23:42:26 2019 +0000
    
    Revert "Purposely overwrite the contents of index.html"
    
    This reverts commit 15d3bded388470c98881a632025bc15190fe9d17.
    

11. Finally, open the index.html file to make sure the content is the correct version.

Reverting isn't the only way to remedy this situation; you could just edit index.html and commit the corrected file. That option is harder if the changes you committed were extensive. In any case, git revert is a good way to signal your intent.

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