Guide to Using Git

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Preface

  • This document is intended to contain the basic information needed for GlueX users and code developers to use git in the GlueX software environment. Many expert operations (e.g. making a tagged release) are excluded. Also, some shortcuts/features are skipped so as not to clutter this document.
  • The steps outlined here can be performed in the order as listed to set everything up properly and to use git.
  • This document has been distilled from information in the below references.

References

First-time Setup

  • The GlueX repositories are hosted on GitHub. See Mark Ito's email about how to create an account on GitHub and how to join the "gluex" team on github: Link

Creating a local clone of the repository

The first thing you need to do is to create a clone of the master repository on your local machine. The "git clone" command pulls all of the code, branches, etc. for the entire history of the project into the current, local directory.

Setup Philosophy

  • In general, you probably want to have several separate copies of the repository built simultaneously on your machine. For example, you may want to have a program running off of a tagged release, and meanwhile develop code separately on a different branch.
  • The recommended way of doing this is to have a wholly separate clone of the repository for each tagged release, in addition to one (or multiple) clone(s) of the repository used for code development.
  • Each new code development project (bug fix, feature addition, etc.) should have it's own code development branch (if not it's own clone of the repository).
    • This way, you can switch between projects/branches as needed, keeping them clean and separated from each other, and merge them back to the "master" branch individually when they're ready.

Examples

To create clones of the master repositories into the directories <mydir>: 

# SIM-RECON
cd $GLUEX_TOP/sim-recon/
git clone https://github.com/jeffersonlab/sim-recon/ <mydir>

# HDDS
cd $GLUEX_TOP/hdds/
git clone https://github.com/jeffersonlab/hdds/ <mydir>

References

Creating & Switching Branches

  • In git, branches are simply pointers to different snapshots of the content of the git repository.
  • By default, the "master" branch is created on your local machine after performing "git clone," but it is not a special or unique branch. There is no inherent definition of a "trunk" in git like there is svn, just a series of branches.
  • However, for GlueX, we treat the remote, "origin," "master" branch of the sim-recon/hdds/etc. repositories (stored on Github) as the "trunk" from which we create tagged releases.
  • "Checking out" a branch replaces the local files/folders with those in the new, current branch. Checking out a different branch is not possible if you have uncommitted changes in your current branch.

Examples

  • To create the branch <mybranch> (whose content will be identical to the current branch) (Note: you must still switch-to/checkout the branch to use it):
git branch <mybranch>
  • To show all of your branches, along with which branch you are currently using (marked by an asterisk (*)): 
git branch
  • To switch-to/checkout the branch <mybranch> (this replaces the local files/folders of your current branch with those of the new branch):
git checkout <mybranch>
  • To create the branch <mybranch> (whose content will be identical to the current branch) and switch-to/checkout it all in one step:
git checkout -b <mybranch>

References

Checking out a Tagged Release

  • When you check out a tagged release, what you're really doing is you're creating a new local branch on your machine that looks exactly like the tagged release. See the example below.
    • If you intend to use this tagged release for frequent running, it is recommended that you create it with an entirely separate repository clone than your development repository, in order to keep the tagged release in a steady state.

Examples

To check out a tagged release <mytag>, giving it a new branch name <mybranch>: 

git checkout -b <mybranch> <mytag>

References

Adding files and/or Committing changes

  • There are two cases where you might want to commit changes: New content and changes to existing content. In both cases, you must first "stage" the change with "git add," before committing it with "git commit."
    • Note that any changes made after "git add" but prior to "git commit" will NOT be committed; run "git add" again on the changed files in order to re-stage them for committing.
    • When you run "git commit" the text editor defined by the environment variable $EDITOR will be launched for you to add commit comments.
  • These operations add/commit the changes to your current, active branch. See the following sections about merging branches and remote repositories to upload these changes to the GitHub repositories.

Examples

To stage a file/folder for the next commit to the current branch (and/or add a new file): 

git add <myfile>

To commit all of the staged files/folders in the current folder to the current branch: 

git commit

To commit all changes to "tracked" files/folders in the directory to the current branch (bypassing the "add" staging: similar to "svn commit"): 

git commit -a

References

Terminology

  • Tracked/untracked files: Untracked files are files that have never been added to git (via git add). Tracked files are ones that have been previously added to git.

Removing Files

  • Use "git rm <myfile>" followed by "git commit" to remove files from the current git branch.

Examples

To remove the file/directory <myfile> from the current branch: 

git rm <myfile>
git commit

References

Merging and Deleting Local Branches

  • Once you finish the project/feature/bugfix for which you created your current branch, you can merge those changes back to your local "master" branch by using the "git merge" command.
  • Since you've finished with this branch, you can then delete it using the "git branch" command.
  • For handling merging conflicts, see the "Basic Merge Conflicts" section of the git book: Link

Examples

To merge the changes committed to branch <my_work_branch> into the local branch <my_master_branch>: 

git checkout <my_master_branch> # Switch to make the master branch active (you can skip this if it's active already)
git merge <my_work_branch> # Merge

To delete the branch <my_work_branch> 

git branch -d <my_work_branch>

References

Updating from Remote Repositories

  • To retrieve updates that have been posted to the main GlueX repositories, type "git fetch origin." This updates your local repository, but doesn't update any of your local branches. You must still merge these changes into the branches that you want to update.
    • The "origin" remote repository is the repository that you cloned-from when you initialized your setup with "git clone."

Examples

To list the remote repositories that your clone is connected to: 

git remote -v

To update your local repository with information from the remote repository "origin" (does not change any of your local branches): 

git fetch origin

To list all of the branches in the remote repository "origin" that your clone knows about (updated via "git fetch" above): 

git remote show origin

To merge the changes from a branch in the remote repository "origin" <remote_branch> into one of your local branches <my_branch>: 

git checkout <my_branch> # Switch to make this branch active (you can skip this if it's active already)
git merge origin/<remote_branch> # Merge remote branch into the active branch

References

Tracking Branches

  • A "tracking" branch is a local branch that is directly linked to a specific remote branch. This makes it easier to update your local branch with changes that others have posted to the remote branch.
  • When you cloned the repository with "git clone," your local "master" branch was automatically created as a tracking branch with respect to the "master" branch in the "origin" repository.

Examples

To create a local tracking branch <mybranch> that tracks the remote branch <remote_branch> on "origin:" 

git checkout -b <mybranch> origin/<remote_branch>

To create a local tracking branch that has the same name as the remote branch <remote_branch> on "origin:" 

git checkout --track origin/<remote_branch>

When a local tracking branch is active, to merge the contents of the remote branch into the local branch: 

git pull

Pushing to Remote Repositories

  • In order for other collaborators to see/use your changes, you must "git push" the branch that contains them to the "origin" GlueX repositories stored on GitHub.
    • The "origin" remote repository is the repository that you cloned-from when you initialized your setup with "git clone."
  • Once you've uploaded (pushed) your branch, in order to update the "master" branch, you need to create a "pull request" on GitHub. This sends an email out to everyone in the group, and one of them will need to accept your changes for them to be incorporated into the "master" branch.
  • Once your changes have been incorporated into the "origin/master" branch on GitHub, you probably want to delete the remote branch.

Examples

Push a local branch <my_local_branch> that contains your changes up to the GlueX "origin" repository on GitHub, changing the branch name to <my_remote_branch>: 

git push origin <my_local_branch>:<my_remote_branch>

Issue a pull request: See Step 6 in Mark's guide at: Link To act on a pull request: See Step 7 in Mark's guide at: Link To delete the branch <my_remote_branch> that you pushed to the GlueX "origin" repository on GitHub: 

git push origin --delete <my_remote_branch>

References

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