Newbie Guide: How To in Git

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Help

How to get help with git commands

  • To get a list of most used commands:
git help
  • To open the Git manual:
man git
  • To see a summary of options for a specific command:
git COMMAND -h
  • To open the manual page for a specific command:
git help COMMAND
or
git COMMAND --help
or
man git-COMMAND
  • To exit code views: hit the 'q' key.


How to use auto-completion

Hit the Tab key as you type to get suggestions. This works with commands and options.

N.B. New Dreamhacks have this set up automatically: see the Pro Git book on how to set it up otherwise.


The Basics

  • To create a branch:
git branch BRANCH_NAME
  • To switch to a branch:
git checkout BRANCH_NAME
  • To switch to the last branch you were on:
git checkout -
  • To create and switch to a branch at once:
git checkout -b BRANCH_NAME
  • To create and switch to a branch stemming from another branch:
git checkout -b BRANCH_NAME OTHER_BRANCH
  • To see unstaged code changes:
git diff
  • To move changes to the staging area:
git add
  • To commit changes:
git commit
  • To add and commit changes at once:
git commit -a
  • To push changes:
git push origin BRANCH_NAME

Upstream Management

How to update to the latest code

  • To grab the latest changes to Dreamwidth's develop branch:
git fetch dreamwidth
git checkout develop && git pull --ff-only dreamwidth develop:develop
  • To push these changes to your fork on Github:
git push origin develop

Note: if you have uncommitted changes when you try to update, you'll get an error message similar to this:

mw@memewidth:~/dw/src/jbackup$ git pull dreamwidth develop:develop
...
From https://github.com/dreamwidth/dw-free
   53294c1..19b8e73  develop    -> develop
error: Your local changes to 'src/jbackup/jbackup.pl' would be overwritten by merge.  Aborting.
Please, commit your changes or stash them before you can merge.

You'll want to stash your changes first, and then try to update again.

Staging Area Management

How to see staged changes

  • To see staged code changes:
git diff --cached
or
git diff --staged
  • To see staged file changes:
git status -s


How to stash your changes

Note: first make sure you're on the right branch using checkout.

  • To put them away:
git stash
  • To bring them back:
git stash pop
  • To see the latest thing you've stashed:
git stash show


How to undo staged changes

  • To unstage a file:
git reset HEAD FILE_PATH

Important: the file is still modified. It's just no longer part of your current staging area.

  • To get rid of the changes after unstaging:
git checkout -- FILE_PATH


How to move and delete files

  • To move files:
git mv OLD_PATH NEW_PATH
  • To delete files:
git rm FILE_PATH


Commit Management

How to see committed changes

  • To see latest commits on local branches:
git branch -v
  • To see committed code changes (latest commit only):
git show
  • To see past commits:
git log
  • To see past commits one at a time:
git log -1

and so on.

  • To see commits for a certain file:
git whatchanged FILE
  • To see what you've done locally in the last 30 days:
git reflog


How to write a good commit message

Git commit messages have a format that's rather peculiar to Git, and we have a further convention of including the issue in the commit message as "Fixes #XXX" - please do include the #! So, ideally your commit messages will look something like this:

    short summary; total 50 chars or less
    
    After a blank line, give a long-form description of the changes.
    You can write a few sentences, several paragraphs, or an essay
    complete with theorems, premises, and supporting references --
    whatever is needed to clearly document the change.

    * bullet points also work

    * describe what the code does

    * if there's a tricky edge case or something weird about the code that's not immediately obvious,
    go into your reasoning

    * try to start each bullet point with a verb

    * use the present form of the verb: "do foo" not "does foo" or "did foo"

    * context is important. Remember that when this is viewed with git log, it will be at least
    one page load away from the issue (and all comments on the issue) and at least two page loads
    away from the pull request. Provide as much context as is necessary

    * comments like "I tested x, y, z" are good but more appropriate for the pull request
    (unless it's a particularly tricky edge case)

    Fixes #XXX.

The first line is used as a summary by tools like git log --oneline; if it is too long, the output of these tools will display oddly.

Additional suggestions on writing commit messages.

If you are making a commit that only needs a short explanation, you can use the -m option:

   git commit -m "This describes the change that I just made. Fixes #963"


How to amend your last commit

Important: you can do this as long as nothing has been pushed.

  • To update a commit with some new changes:
git commit --amend
  • To do so and reuse your last commit message:
git commit --amend -C HEAD


How to undo committed changes

Important: you can do this as long as nothing has been pushed. Also make sure there's a commit to go back to before you do this or you'll end up in detached HEAD state, which is as bad as it sounds.

  • To reset everything to the previous commit:
git reset --hard

or:

git reset --hard HEAD~1

You can increment the number to go back to even earlier commits.


How to push commits to the release branch

Emergency fixes for issues that pop up right after a code push go into the release branch for the code push instead of the main develop branch. That way, regular development of features can go on as usual while the push-related issues can be fixed and pushed live on the site ASAP.

  • First create a copy of the release branch:
git checkout -t dreamwidth/release-X.X
X-X is the number given to the release on the GitHub repo branch. Make sure it matches.
  • Create a branch based on the release branch:
git checkout release-X.X -b BRANCH_NAME
  • Follow the usual steps: edit, add, commit, push.
  • Select 'compare and review' then click on 'edit' to select the release branch as your base branch (you'll see all changes merged into the release branch otherwise). Send the request when you're done reviewing.


How to squash several commits into one

If, for some reason, you'd like several commits to be just one, you can squash them. This is not reversible so proceed with caution.

  1. Make sure everything is up-to-date.
  2. Make sure you're on the correct branch using git checkout.
  3. Load the interactive rebase interface using
    git rebase -i develop
  4. The interface will show you all the successive commits on this branch, from the oldest at the top to the most recent at the bottom.

From there you have several options:

  • If you want to be able to edit all commit messages or merge them in some fashion, edit the work 'pick' to the word 'squash' for the ones you want to squash into the previous commit. You'll be then shown all commit messages and you'll be able to edit them, comment the lines you want to hide, etc.
  • If you want to edit the commit message of your master commit but discard all the other ones, use 'reword' for your master commit then 'fixup' for the other ones.
  • If you want to keep your master message as-is and discard the rest, use 'pick' and 'fixup' instead.


  • Note that if you had already pushed some changes to GitHub, you will need to force a push to get it updated:
git push -f origin BRANCH_NAME

Also, git ready has a nice guide to squashing commits using the interactive rebaser (git rebase -i).

  • The interactive rebaser can also do many other nifty and powerful things. You can change commit messages, edit past commits, reorder commits, or discard individual commits entirely.


How to copy a commit from one branch to another

Important: don't do this if your new branch isn't empty or if what you have will conflict with the new additions.

  • Create the new branch if it doesn't exist already.
  • On the old branch, find your commit hash using git reflog.
  • Switch to the new branch then use:
git cherry-pick HASH

How to add/commit only part of a file

There are times when you want to commit only some of the changes you've made to a file. Maybe you've fixed one thing, and are in the midst of fixing a second thing somewhere else in that file when you decide you want to commit the first change.

You don't have to back out the work you've done on the second fix in order to commit the first change by itself. Use the interactive option of git add:

# consider all changed files for addition 
git add -i 
# consider only the files specified 
git add -i FILE [FILE2 FILE3 ...]

You'll be shown the current staging status of the file(s), and how many lines in each of them are staged (added) or unstaged (not added yet).

   twilight:~/temp rick$ git add -i
              staged     unstaged path
     1:    unchanged        +9/-8 bar.pl
     2:    unchanged        +2/-1 foo.pl
     3:    unchanged        +2/-0 index.html
   
   *** Commands ***
     1: [s]tatus     2: [u]pdate     3: [r]evert     4: [a]dd untracked
     5: [p]atch      6: [d]iff       7: [q]uit       8: [h]elp
   What now> 

There are a lot of commands, but you really only need very few of them. Too, there's help available in each menu -- you can enter ? at any prompt for help, in addition to any visible help options.

  • 1: shows you the current staging status, just like when git add -i started.
  • 2: stage (add) whole files
  • 3: unstage (un-add) whole files
  • 4: add a currently-untracked file
  • 5: stage individual chunks in a file bit-by-bit
  • 6: show the diff between what's been staged so far & the previous commit

Number 5 (patch) is the biggest winner of all these, and usually why you're running the command at all. Select 5 and you'll be presented with a menu like this one:

              staged     unstaged path
     1:    unchanged        +9/-8 [b]ar.pl
     2:    unchanged        +2/-1 [f]oo.pl
     3:    unchanged        +2/-0 [i]ndex.html
   Patch update>> 

Pick the file or files you want to part-stage by entering their number(s), then hitting enter. When you're done picking files, hit enter once more at the empty Patch Update>> prompt. The program will show you every change in the files you've selected, one at a time, and ask you if you want to add it, eg:

   diff --git a/index.html b/index.html
   index 32870ee..416e0bd 100644
   --- a/index.html
   +++ b/index.html
   @@ -8,6 +8,7 @@
    
    
        <link rel="stylesheet" type="text/css" href="./css/base.css" />
   +    <link rel="stylesheet" type="text/css" href="./css/frontpage.css" />
        
        <title>Welcome!</title>
      </head>
   Stage this hunk [y/n/a/d/e/?]? 

Hit y to add this change, n to not add it for now. There are many more options, like splitting a change in two or adding every change left in the file -- you can hit ? to see those.

When you're done, you're taken back to the main menu. If you're finished, hit 7 to quit. If you want, you can then review everything you've added by giving the command

git diff --cached


Branch Management

How to see branches

  • To check which local branch you're on (noted with an asterisk):
git branch
  • To see local and remote branches (including deleted ones):
git branch -a
  • To see branches on a graph: go to your profile page on github.com, click dw-free or dw-nonfree then on Network. Hit Shift and the right arrow to go to the most current part of the graph.
  • To see merged branches:
git branch --merged
  • To see unmerged branches:
git branch --no-merged

Note: you can also see merged and unmerged branches on GitHub. On your profile, click on the Repositories tab, select yours then click on Branches (and view merged branches).

  • To see where local branches stem off, which branch is also on GitHub and what is the latest commit on each branch and its abbreviated hash ref:
git log --all --abbrev-commit --decorate --oneline  --simplify-by-decoration

Note that git log has many options letting you do wonderful things which might help you better.

How to create a new branch for feature development / bugfixes

All code changes should happen in a branch, whether it's a huge long-running feature or a tiny bugfix.

Before you create your branch, make sure your copy of develop is up-to-date (it will save you headaches later). Then create your branch:

git checkout develop -b BRANCH_NAME-bug-XXX

Choose a descriptive branch name you can keep track of--in this example, it's the bug number being worked on, plus a couple of keywords so you're not relying solely on memorizing bug numbers. Remember you can use auto-completion to make it easier to switch to your branch later.

In addition, you can also set up a script to automatically insert the issue number into your commit message based on your branch name.


How to rename and delete branches

  • To rename a local branch:
git branch -m OLD_NAME NEW_NAME

Important: if you had already pushed some changes to GitHub, this will create a new identical branch there. You will need to delete the old one using the method described below.

  • To delete a local branch or a merged branch:
git branch -d BRANCH_NAME

Important: the merge will only be detected if you've updated your code. Otherwise, you'll get an error saying the branch isn't fully merged.

  • To delete an unmerged branch:
git branch -D BRANCH_NAME
  • To delete a branch on GitHub:
git push origin :BRANCH_NAME

Note: you can also do this directly on GitHub once your branch has been merged into develop. Just click on the pull request (from the Activity list on your profile for example), scroll down and it'll ask if you want to delete the branch.


How to pull the latest changes from develop into your branch

Important: don't do this if your branch isn't empty or if what you have will conflict with the new additions.

If it's been a while since you've worked on your bug, you may want to or need to bring your branch up to date with any changes that have happened in develop since you initially forked your branch.

  • To update your branch so it has all the new code which has been added to develop since you created it:
git checkout BRANCH_NAME
git pull --rebase --ff-only dreamwidth develop
  • You can also do this with other branches such as the current release branch by checking out the release branch then pulling from release-X.X instead of develop.

pull --rebase incorporates any new changes from develop into your branch, and it also reorganizes your changes so that changes in your branch appear to start from current develop, instead of where develop was when you initially started your branch. (Neat!) This can make it much easier to merge your branch into Dreamwidth's main develop branch.

  • If you had already pushed your branch to GitHub, you will need to force push your changes:
git push -f origin BRANCH_NAME


How to change where your branch stems off

Important: depending on where you put it what you have may conflict with what's already there. You'll then have to resolve conflicts manually or abort the rebase.

  • To change the point of origin of a branch:
git rebase --onto NEW_BASE OLD_BASE BRANCH_NAME

For example, if you want to move something from develop to a release branch you'd use:

git rebase --onto release-X.X develop BRANCH_NAME


Pull Request Management

How to submit a pull request

Go to your version of the repository (dw-free or dw-nonfree) that you want to send upstream. By default they should be at:

These repositories are separate, so if you have made changes to both of them, you will have to submit pull requests for both of them.

Find your branch in the drop-down menu then click on Compare and Pull Request right above it. Check your request one last time then click on Send Pull Request. Make sure you've included the sentence "Fixes #XXX", where #XXX is the issue number in your commit message - Github does some magic behind the scenes which makes record-keeping/issue-tracking much easier!

All pull requests are reviewed by a senior Dreamwidth developer before committing (or returning for further work).


How to update a pull request after it's been reviewed

Pull requests all go through review, and it is common to have multiple passes with suggestions to improve the functionality, tweak the interface, or improve the code. This means that you'll need to go back to the relevant branch and add new commits.

  • If you're not on the right branch, switch to the branch you want to work on
  • Make requested changes, commit
  • Push your changes live (the pull request will automatically update with your new commits)
  • Comment on the pull request so that the reviewer is aware that something has changed. Reviewers aren't notified of new commits, but are notified of new comments.


How to modify existing commits in a pull request

Sometimes the reviewer requests cleanup of existing commits -- situations where that may happen are if there are a lot of cleanup commits ("removed debug log"), or if there are suggested improvements to the commit message (referring to the issue number, clarity of message, etc).

In that case, follow the instructions under #How to squash several commits into one, which describes how to merge multiple commits together, and how to reword the messages of existing commits.


Git Configuration

How to create custom keywords for your most-used commands

  • Tired of (mis)typing the same things over and over? You can create keywords for them. Open .gitconfig in your root folder. Add this at the bottom and edit as desired:
[alias]
	KEYWORD1= COMMAND1
	KEYWORD2= COMMAND2
Warning! Make sure the keyword you're using isn't already a git command.
  • You can then use your keyword instead of typing the full command (e.g. git c instead of git checkout -b).


How to list your custom keywords

Because who doesn't forget them? :)

git config --get-regexp alias


How to configure git

See Git settings for some of the most useful settings.


How to create a default commit message

Easy peasy! In your root folder, create a file called .gitmessage.txt with whatever default message you wanna use then edit .gitconfig to use it:

git config --global commit.template $HOME/.gitmessage.txt


How to automatically insert the issue number into your commit message

Important! This will only work if 'bug-XXX' where XXX is the issue number is in your branch name. This is meant as a way not to have to type it or paste it *again* in your commit messages.

Go to ~/dw/.git/hooks/ and create a filed called prepare-commit-msg. Paste this gist made by the brilliant [info]fu and save. Finally make it executable by running:

chmod u+x ~/dw/.git/hooks/prepare-commit-msg
N.B. This can be used in conjunction with the default commit message mentioned in the previous section.


Troubleshooting

Why am I getting 'Permission denied'?

Before running any of the git commands on this page, you will need to ensure you are somewhere within the $LJHOME directory tree. On Dreamhacks, if you are not within this directory tree, you may receive errors like this:

   fatal: Unable to create '/dreamhack/.git/refs/heads/dj.lock': Permission denied

This occurs because the Dreamhack machine uses its own git repository for its code too, and Git is thinking that you wanted to use this repository instead of your own personal repository. To fix this, simply change to the $LJHOME directory:

cd $LJHOME

The commands should now work without issue.

Untangling messes

If your account or branch is in some kind of unfortunate state that you do not know how to recover from:

  • try not to panic
  • try not to blame yourself -- this is a very common situation, especially while first getting used to git.
  • feel free to ask for help, particularly in [info]dw_dev_training or, for real-time support, in #dreamwidth-dev; it can help to come prepared with a pastebin link of what's going on in your account, and explain what you're trying to do.


References

Stack Overflow: one of the best places to find out if there's a command for what you wanna do.

Command Index