Changing History

Changing Git History: Amend, Reset, and Rebase

Git allows you to modify your project’s history, but use these features cautiously, especially when collaborating. Changes to history can be confusing for others working on the same project.

Amending the Last Commit

(git commit --amend)

This is used to modify the last commit. Useful for small corrections or adding forgotten files to the last commit without creating a new commit.

• git commit --amend: Opens your default text editor to modify the commit message. Save and close to amend the commit.
• git commit --amend -m "New commit message": Directly changes the commit message from the command line.
• git commit --amend --no-edit: Keeps the existing commit message unchanged.

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Resetting

(git reset)

This moves the HEAD pointer to a previous commit, effectively “rewinding” your history.

• git reset <commit-hash>: Moves the HEAD pointer to the specified commit. Changes made after this commit will be unstaged but not deleted from your working directory. You can then stage and commit them again. This is the safer, “soft” reset.
• git reset --hard <commit-hash>: A more dangerous operation that discards all changes made after the specified commit. Use with extreme caution.

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Rebasing

(git rebase)

Rebase allows you to rewrite the commit history by changing the order of commits or combining them. It’s particularly useful for cleaning up a messy history or integrating changes from one branch into another in a cleaner way.

• Interactive Rebase (git rebase -i HEAD~<n>): Opens your text editor showing the last n commits. You can reorder commits, squash multiple commits into one, or use the fixup command to merge a commit’s changes into the previous commit while discarding its message. “HEAD3” means the three commits before the current head. “HEAD” is equivalent to “HEAD~1”.

  • pick: Keep the commit as is.
  • reword: Change the commit message.
  • edit: Allows you to further modify the commit’s changes.
  • squash: Combine this commit with the previous one.
  • fixup: Combine this commit with the previous one, discarding the commit message.

Important Considerations:

• Collaboration: Avoid changing history on shared branches; it can cause significant issues for collaborators.
• Safety: The --hard option of git reset is highly destructive. Use it only if you understand the risks and have a backup.
• Practice: Practice these commands in a safe environment (e.g., a local repository or a test repository on GitHub) before applying them to your main projects. git status and git log are your friends.

These powerful commands offer significant control over your project history, enabling the ability to clean up messy commits or undo unwanted changes. However, responsible use is critical to avoid errors and complications, particularly in a collaborative setting.