A [guide for astronauts](http://www.jsc.nasa.gov/news/columbia/fr_generic.pdf) (now, programmers using git) about what to do when things go wrong.
> *Flight Rules* are the hard-earned body of knowledge recorded in manuals that list, step-by-step, what to do if X occurs, and why. Essentially, they are extremely detailed, scenario-specific standard operating procedures. [...]
> NASA has been capturing our missteps, disasters and solutions since the early 1960s, when Mercury-era ground teams first started gathering "lessons learned" into a compendium that now lists thousands of problematic situations, from engine failure to busted hatch handles to computer glitches, and their solutions.
— Chris Hadfield, *An Astronaut's Guide to Life*.
For clarity's sake all examples in this document use a customized bash prompt in order to indicate the current branch and whether or not there are staged changes. The branch is enclosed in parentheses, and a `*` next to the branch name indicates staged changes.
[](https://gitter.im/k88hudson/git-flight-rules?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
- [I tried to push my amended commit to a remote, but I got an error message](#i-tried-to-push-my-amended-commit-to-a-remote-but-i-got-an-error-message)
- [I pulled from/into the wrong branch](#i-pulled-frominto-the-wrong-branch)
- [I want to discard local commits so my branch is the same as one on the server](#i-want-to-discard-local-commits-so-my-branch-is-the-same-as-one-on-the-server)
- [I committed to master instead of a new branch](#i-committed-to-master-instead-of-a-new-branch)
- [I made several commits on a single branch that should be on different branches](#i-made-several-commits-on-a-single-branch-that-should-be-on-different-branches)
- [I want to delete local branches that were deleted upstream](#i-want-to-delete-local-branches-that-were-deleted-upstream)
- [I accidentally deleted my branch](#i-accidentally-deleted-my-branch)
- [I want to delete a branch](#i-want-to-delete-a-branch)
- [I want to change a file name's capitalization, without changing the contents of the file.](#i-want-to-change-a-file-names-capitalization-without-changing-the-contents-of-the-file)
- [I want to remove a file from git but keep the file](#i-want-to-remove-a-file-from-git-but-keep-the-file)
Let's say that you just blindly committed changes with `git commit -a` and you're not sure what the actual content of the commit you just made was. You can show the latest commit on your current HEAD with:
This is particularly useful when you have an open patch and you have committed an unnecessary file, and need to force push to update the patch on a remote. The `--no-edit` option is used to keep the existing commit message.
If you need to delete pushed commits, you can use the following. However, it will irreversibly change your history, and mess up the history of anyone else who had already pulled from the repository. In short, if you're not sure, you should never do this, ever.
This only works if you haven't pushed. If you have pushed, the only truly safe thing to do is `git revert SHAofBadCommit`. That will create a new commit that undoes all the previous commit's changes. Or, if the branch you pushed to is rebase-safe (ie. other devs aren't expected to pull from it), you can just use `git push --force-with-lease`. For more, see [the above section](#deleteremove-last-pushed-commit).
Note that, as with rebasing (see below), amending **replaces the old commit with a new one**, so you must force push (`--force-with-lease`) your changes if you have already pushed the pre-amended commit to your remote. Be careful when you do this –*always* make sure you specify a branch!
In general, **avoid force pushing**. It is best to create and push a new commit rather than force-pushing the amended commit as it has will cause conflicts in the source history for any other developer who has interacted with the branch in question or any child branches. `--force-with-lease` will still fail, if someone else was also working on the same branch as you, and your push would overwrite those changes.
If you are *absolutely* sure that nobody is working on the same branch or you want to update the tip of the branch *unconditionally*, you can use `--force` (`-f`), but this should be avoided in general.
`-p` will work for short. This will open interactive mode. You would be able to use the `s` option to split the commit - however, if the file is new, you will not have this option. To add a new file, do this:
Then, you will need to use the `e` option to manually choose which lines to add. Running `git diff --cached` will show you which lines you have staged compared to which are still saved locally.
`HEAD^` is short for `HEAD^1`. This stands for the first parent of `HEAD`, similarly `HEAD^2` stands for the second parent of the commit (merges can have 2 parents).
Alternatively, if you don't want to use `HEAD^`, find out what the commit hash you want to set your master branch to (`git log` should do the trick). Then reset to that hash. `git push` will make sure that this change is reflected on your remote.
(solution)$ git add -A && git commit -m "Adding all changes from this spike into one big commit."
```
When you want to put it into a branch (maybe feature, maybe `develop`), you're interested in keeping whole files. You want to split your big commit into smaller ones.
Say you have:
* branch `solution`, with the solution to your spike. One ahead of `develop`.
* branch `develop`, where you want to add your changes.
You can solve it bringing the contents to your branch:
Note: Spike solutions are made to analyze or solve the problem. These solutions are used for estimation and discarded once everyone gets clear visualization of the problem. ~ [Wikipedia](https://en.wikipedia.org/wiki/Extreme_programming_practices).
Now, let's *cherry-pick* the commit for bug #21 on top of our branch. That means we will be applying that commit, and only that commit, directly on top of whatever our head is at.
At this point, there is a possibility there might be conflicts. See the [**There were conflicts**](#merge-conflict) section in the [interactive rebasing section above](#interactive-rebase) for how to resolve conflicts.
### I want to delete local branches that were deleted upstream
Once you merge a pull request on github, it gives you the option to delete the merged branch in your fork. If you aren't planning to keep working on the branch, it's cleaner to delete the local copies of the branch so you don't end up cluttering up your working checkout with a lot of stale branches.
If you're regularly pushing to remote, you should be safe most of the time. But still sometimes you may end up deleting your branches. Let's say we create a branch and create a new file:
You may have merged or rebased your current branch with a wrong branch, or you can't figure it out or finish the rebase/merge process. Git saves the original HEAD pointer in a variable called ORIG_HEAD before doing dangerous operations, so it is simple to recover your branch at the state before the rebase/merge.
Unfortunately, you have to force push, if you want those changes to be reflected on the remote branch. This is because you have fast forwarded your commit, and changed git history. The remote branch won't accept changes unless you force push. This is one of the main reasons many people use a merge workflow, instead of a rebasing workflow - large teams can get into trouble with developers force pushing. Use this with caution. A safer way to use rebase is not to reflect your changes on the remote branch at all, and instead to do the following:
Let's suppose you are working in a branch that is/will become a pull-request against `master`. In the simplest case when all you want to do is to combine *all* commits into a single one and you don't care about commit timestamps, you can reset and recommit. Make sure the master branch is up to date and all your changes committed, then:
If you aren't working against another branch you'll have to rebase relative to your `HEAD`. If you want to squash the last 2 commits, for example, you'll have to rebase against `HEAD~2`. For the last 3, `HEAD~3`, etc.
Then you replace `pick` commands with any in the list above, and you can also remove commits by removing corresponding lines.
For example, if you want to **leave the oldest (first) commit alone and combine all the following commits with the second oldest**, you should edit the letter next to each commit except the first and the second to say `f`:
If you want to combine these commits **and rename the commit**, you should additionally add an `r` next to the second commit or simply use `s` instead of `f`:
`--no-commit` performs the merge but pretends the merge failed and does not autocommit, giving the user a chance to inspect and further tweak the merge result before committing. `no-ff` maintains evidence that a feature branch once existed, keeping project history consistent.
Sometimes you have several work in progress commits that you want to combine before you push them upstream. You don't want to accidentally combine any commits that have already been pushed upstream because someone else may have already made commits that reference them.
This will do an interactive rebase that lists only the commits that you haven't already pushed, so it will be safe to reorder/fix/squash anything in the list.
This will tell you if any commits are in one but not the other, and will give you a list of any nonshared between the branches. Another option is to do this:
You will need to resolve the differences between the code that was added in your new commit (in the example, everything from the middle line to `new-commit`) and your `HEAD`.
If you want to keep one branch's version of the code, you can use `--ours` or `--theirs`:
```sh
(master*)$ git checkout --ours README.md
```
- When *merging*, use `--ours` to keep changes from the local branch, or `--theirs` to keep changes from the other branch.
- When *rebasing*, use `--theirs` to keep changes from the local branch, or `--ours` to keep changes from the other branch. For an explanation of this swap, see [this note in the git documentation](https://git-scm.com/docs/git-rebase#git-rebase---merge).
If the merges are more complicated, you can use a visual diff editor:
After you have resolved all conflicts and tested your code, `git add` the files you have changed, and then continue the rebase with `git rebase --continue`
If someone has sent you a pull request on GitHub, but then deleted their original fork, you will be unable to clone their repository or to use `git am` as the [.diff, .patch](https://github.com/blog/967-github-secrets) urls become unavailable. But you can checkout the PR itself using [GitHub's special refs](https://gist.github.com/piscisaureus/3342247). To fetch the content of PR#1 into a new branch called pr_1:
On OS X and Linux, your git configuration file is stored in ```~/.gitconfig```. I've added some example aliases I use as shortcuts (and some of my common typos) in the ```[alias]``` section as shown below:
### I want to cache a username and password for a repository
You might have a repository that requires authentication. In which case you can cache a username and password so you don't have to enter it on every push / pull. Credential helper can do this for you.
So, you're screwed - you `reset` something, or you merged the wrong branch, or you force pushed and now you can't find your commits. You know, at some point, you were doing alright, and you want to go back to some state you were at.
This is what `git reflog` is for. `reflog` keeps track of any changes to the tip of a branch, even if that tip isn't referenced by a branch or a tag. Basically, every time HEAD changes, a new entry is added to the reflog. This only works for local repositories, sadly, and it only tracks movements (not changes to a file that weren't recorded anywhere, for instance).
```sh
(master)$ git reflog
0a2e358 HEAD@{0}: reset: moving to HEAD~2
0254ea7 HEAD@{1}: checkout: moving from 2.2 to master
c10f740 HEAD@{2}: checkout: moving from master to 2.2
```
The reflog above shows a checkout from master to the 2.2 branch and back. From there, there's a hard reset to an older commit. The latest activity is represented at the top labeled `HEAD@{0}`.
If it turns out that you accidentally moved back, the reflog will contain the commit master pointed to (0254ea7) before you accidentally dropped 2 commits.
Using git reset it is then possible to change master back to the commit it was before. This provides a safety net in case history was accidentally changed.
* [git-workflow](https://github.com/asmeurer/git-workflow) - [Aaron Meurer](https://github.com/asmeurer)'s howto on using git to contribute to open source repositories
* [GitHub as a workflow](http://hugogiraudel.com/2015/08/13/github-as-a-workflow/) - An interesting take on using GitHub as a workflow, particularly with empty PRs
* [git-fire](https://github.com/qw3rtman/git-fire) - git-fire is a Git plugin that helps in the event of an emergency by adding all current files, committing, and pushing to a new branch (to prevent merge conflicts).
* [GitExtensions](https://github.com/gitextensions/gitextensions) - a shell extension, a Visual Studio 2010-2015 plugin and a standalone Git repository tool.
