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Fixing Git Mistakes
Posted on August 31, 2020 in Git by Matt Jennings

What Happens when you Git Checkout a Branch?

1. Change HEAD to point to the new branch
2. Copy the commit snapshot to the staging area (also called the index)
3. Update the working area with the branch contents

What Happens when you Git Checkout — File?

• Replace the working area copy with the version from the current staging area.
• Overwrite the working area file with the staging area version from the last commit:
  git checkout -- <file_path>

Git Clean

• Git clean will clear working area by deleting untracked files.
• WARNING: This operation cannot be undone!
• Use the –dry-run flag to see what would be deleted – see example:
  • See what files (NOT directories) would be deleted:
    git clean --dry-run
  • See what files and directories would be deleted:
    git clean -d --dry-run
• Delete a file and directory using git clean:
  git clean -d -f

Git Reset

• By default, git performs a:
  git reset --mixed
• For commits:
  • Move the HEAD pointer, optionally modifies files
• For file paths:
  • Does not move the HEAD pointer, modifies files

Git Reset –mixed: Move HEAD Copy Files to Stage

• git reset HEAD~
• git reset --mixed HEAD~

Git Rest –hard: Move HEAD, Copy Files to Stage and Working

• git reset --hard HEAD~
• Warning: This overwrites files and cannot be undone!

Danger: Git Reset Can Change History!

• Warning: Never push changed history to a shared or public repository!

Undo a Git Reset with ORIG_HEAD

In case of an accidental git reset:

• Git keeps the previous value of HEAD in a variable called:
  ORIG_HEAD
• To go back to the way things were:
  git reset ORIG_HEAD

Git Revert – The “Safe” Reset

• Git revert creates a new commit that introduces the opposite changes from the specified commit.
• The original commit stays in the repository.
• Revert does not change history.
• Example code:
  git revert 2b0b3f2
• A screen will open in Vim and then I’ll save the text (:wq), do a commit, and push it to the repo.

Modify a File and then Checkout it Out to a State Just Before it was Modified

• echo "Bad Data" > hello.template
• git checkout -- hello.template