Friday, December 18, 2015

Git cheat sheet

Creating a feature branch

Creating a feature branch is a good way to keep your testing out of the main branch. You can hack away at your code without disturbing the general workflow.
The following command will create a feature branch that tracks master. Pushing it with the -u origin flag will autmatically make your local version of the branch track the remote version:
     $ git checkout master && git pull
     $ git checkout -t -b "some-feature-branch-name"
     $ git push -u origin "some-feature-branch-name"
Also, since this is a feature branch you're free to do force commits and cleanup your git history.
You can see what your branches are tracking and what their origin is with the following command:
git branch -vv
  1432-rb-force-safety-switch 62d5af7 [origin/1432-rb-force-safety-switch] Refuse rb if path contains keys.
* develop                     5f56434 [origin/develop: ahead 233, behind 2] Merge branch 'release-1.8.12'
And to see where "origin" points to:
$ git remote -v
origin (fetch)
origin (push)
upstream (fetch)
upstream (push)
In the above example, I can push to either "upstream" (which in this case is the official aws repo), or "origin", which is my forked repo.

Creating a Git Tag

A tag is a point-in-time reference to a git branch. Tags are immutable snapshots of the repo that can't be altered once they are created (though they can be deleted and recreated). They are useful for tasks such as deployments or ensuring your work won't be altered by others.
    # This will create a tag called "mysql-1380235429"
    $ git tag -a -m "Deploying mysql update" mysql-`date +%s`
    $ git push --tags
Now the tag can be checked out in the usual method.
    $ git checkout mysql-1380235429

Preparing Your Branch for a Pull Request

A pull request should be done before anything is merged into the master branch.
Before asking someone to review your work, you should take a few minutes and make sure it's really finished. You'd be surprised what things can slip through.

Diff Against Master

The first thing you want to do is diff your branch against the master branch. This allows you to catch simple bugs before pushing anything upstream.
git diff master
This will tell you exactly what's different between your branch and the master branch. It will also highlight things such as trailing whitespace.

Rebasing your branch against master (or a different branch)

You can think of rebasing as doing the following actions: 1. Take all recent changes and stash them away 2. Pull down the most recent changes from a different branch 3. Attempt to apply your stashed changes on top of the new changes one at a time.
Here's how to rebase your branch against master:
git checkout master
git pull
git checkout my_feature_branch
git rebase master
git push origin +my_feature_branch
Many times there's conflicts in this process if there were multiple changes to the same file. The way to fix a conflict is to change it during the rebase and add it again:
(fix the conflicts within the file)
git add some_conflicted_file
git rebase --continue
If you think there's a problem then you can abort the rebase with --abort.

Squashing Commits

It's important that you branch is tidy because it makes rolling back bad changes a lot easier. You can squash all of your commits into one or two commits using the rebase command.
First, run git log and find the commit that you want to squash into. Usually this is the first commit on your feature branch.
Next, interactively rebase against that commit:
git rebase --interactive shdf8032hfohsdofhsdohf80h^
This will rebase every commit after the sha.
Follow the instructions for rebasing. Usually you just want to change the "pick" to a "squash" or "s". In the below example, all commits will be squashed into the top commit (which is the oldest):
pick e775ebe Refactor regex to avoid duplication
s 3bb23fd Add support for spaces within unquoted values
s e36d71a Support '-' char in a key name
s 16eda81 Remove unused import in test module
s 403c7ec Add bugfixes to changelog
You will have a chance to rewrite the commit message to better include all of the changes.
After you're finished, do a diff against master again just to make sure things don't go wrong. Then force push your branch to origin.
# Make sure it still looks good
git diff master
git push origin +my_feature_branch

Send Out the PR

Go to and find your branch. Compare it with master and send out the PR. You should ask someone specifically to review your changes and include the following information:
  • Why did you change this?
  • What have you changed?
  • How have you tested these changes?
  • What are the risks involved with these changes?

Oh no! I rebase my branch and lost a lot of history! I'm doomed!

Fear not. With git nothing is ever truly lost. If you made some mistake and you're currently in the rebase process then you can abort it with git rebase --abort. If you've already commited, pushed, etc, then you can use the fantastic git reflog tool to go back to a different commit.

Using git reflog

In the following example, I'm going to force my branch back to the moment before I rebased and broke everything:
First, find the commit that came right before your rebase:
git reflog
5f56434 HEAD@{0}: pull upstream master: Fast-forward
ed610bc HEAD@{1}: checkout: moving from 1432-rb-force-safety-switch to develop
62d5af7 HEAD@{2}: rebase -i (finish): returning to refs/heads/1432-rb-force-safety-switch
62d5af7 HEAD@{3}: rebase -i (squash): Refuse rb if path contains keys.
781b4da HEAD@{4}: rebase -i (start): checkout 781b4da0dcc65736297464dd73da442daad4cf2c^
4350e25 HEAD@{5}: commit: Use two vars for readability. <---- ding ding ding
781b4da HEAD@{6}: checkout: moving from ed610bc9d38244feeaf0b640781da8ab01808f4e to 1432-rb-force-safety-switch
Next, we'll checkout that sha and then force push it
git checkout 4350e25
git log # make sure it's what you want
git push +some_branch

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