Git tutorial undoing changes
- 1. Git Tutorial – Undoing Changes Bryan Lin 2013/11/25
- 2. Agenda Overview git checkout git revert git reset git clean
- 3. Overview This tutorial provides all of the necessary skills to work with previous revisions of a software project. First, it shows you how to explore old commits, then it explains the difference between reverting public commits in the project history vs. resetting unpublished changes on your local machine.
- 4. git checkout Serves three distinct functions: ◦ checking out files ◦ checking out commits ◦ checking out branches
- 5. git checkout Usage: ◦ git checkout master Return to the master branch ◦ git checkout <commit> <file> Check out a previous version of a file ◦ git checkout <commit> Update all files in the working directory to match the specified commit
- 6. git checkout Disscusion: ◦ git checkout is an easy way to ―load‖ any of these saved snapshots onto your development machine ◦ Checking out an old commit is a read-only operation
- 7. git checkout Disscusion: ◦ detached HEAD state: when you check out a previous commit, HEAD no longer points to a branch—it points directly to a commit
- 8. git checkout Disscusion: ◦ On the other hand, checking out an old file does affect the current state of your repository. You can re-commit the old version in a new snapshot as you would any other file
- 9. git checkout Example: ◦ Viewing an Old Revision git log –oneline you can see the result like the following: Checkout this commit This is ―commit‖
- 10. git checkout Example: ◦ Viewing an Old Revision Use git checkout to view the ―Make some import changes to hello.py‖ ◦ git checkout a1e8fb5 Get back to the ―current‖ state of your project ◦ git checkout master
- 11. git checkout Example: ◦ Checking Out a File Only wanted to see the hello.py file from the old commit ◦ git checkout a1e8fb5 hello.py Discard this change ◦ git checkout HEAD hello.py
- 12. git checkout Exercise: ◦ Create a git repository, and add 1.txt, 2.txt, 3.txt for commit 1, b.txt for commit 2 commit1 commit2
- 13. git checkout Exercise: ◦ ◦ ◦ ◦ ◦ ◦ checkout commit1 revert to master checkout 2.txt of commit1 commit 2.txt checkout 1.txt discard the change of 1.txt
- 14. git revert The git revert command undoes a committed snapshot Appends a new commit with the resulting content
- 15. git revert Usage ◦ git revert <commit> ◦ Generate a new commit that undoes all of the changes introduced in <commit>, then apply it to the current branch
- 16. git revert Discussion ◦ Reverting should be used when you want to remove an entire commit from your project history, such as fixing the bug of this commit, then commit a new snapshot.
- 17. git revert Discussion ◦ Reverting vs. Resetting It's important to understand that git revert undoes a single commit—it does not "revert" back to the previous state of a project by removing all subsequent commits. In Git, this is actually called a reset, not a revert
- 18. git revert Discussion ◦ Reverting vs. Resetting
- 19. git revert Example ◦ commits a snapshot, then immediately undoes it with a revert
- 20. git revert Example ◦ This can be visualized as the following:
- 21. git revert Example ◦ commits a snapshot, then immediately undoes it with a revert
- 22. git revert Example ◦ Note that the 4th commit is still in the project history after the revert. Instead of deleting it, git revert added a new commit to undo its changes. As a result, the 3rd and 5th commits represent the exact same code base, and the 4th commit is still in our history just in case we want to go back to it down the road
- 23. git reset Discussion ◦ If git revert is a ―safe‖ way to undo changes, you can think of git reset as the dangerous method. When you undo with git reset(and the commits are no longer referenced by any ref or the reflog), there is no way to retrieve the original copy—it is a permanent undo
- 24. git reset Usage ◦ git reset <file> Remove the specified file from the staging area, but leave the working directory unchanged ◦ git reset Reset the staging area to match the most recent commit, but leave the working directory unchanged
- 25. git reset Usage ◦ git reset –hard Reset the staging area and the working directory to match the most recent commit ◦ git reset <commit> Move the current branch tip backward to <commit>, reset the staging area to match, but leave the working directory alone ◦ git reset --hard <commit>
- 26. git reset Usage ◦ git reset --hard <commit> Move the current branch tip backward to <commit> and reset both the staging area and the working directory to match
- 27. git reset Discussion ◦ Whereas reverting is designed to safely undo a public commit, git reset is designed to undo local changes
- 28. git reset Don’t Reset Public History ◦ Removing a commit that other team members have continued developing poses serious problems for collaboration
- 29. git reset
- 30. git reset Examples ◦ Unstaging a File Assumes you have two files called hello.py and main.py that you’ve already added to the repository
- 31. git reset Examples ◦ Unstaging a File
- 32. git reset Examples ◦ Removing Local Commits
- 33. git clean The git clean command removes untracked files from your working directory
- 34. git clean Usage ◦ git clean –n This will show you which files are going to be removed without actually doing it ◦ git clean –f Remove untracked files from the current directory. The -f (force) flag is required unless the clean.requireForce configuration option is set to false (it's true by default). This will not remove untracked folders or files specified by .gitignore.
- 35. git clean Usage ◦ git clean -f <path> Remove untracked files, but limit the operation to the specified path ◦ git clean –df Remove untracked files and untracked directories from the current directory ◦ git clean –xf Remove untracked files from the current directory as well as any files that Git usually ignores
- 36. git clean Discussion ◦ The git reset --hard and git clean -f commands are your best friends after you’ve made some embarrassing developments in your local repository and want to burn the evidence ◦ The git clean command can also be useful for cleaning up the working directory after a build
- 37. git clean Example ◦ Assumes you’ve already committed a few snapshots and are experimenting with some new developments
- 38. FAQ