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   gittutorial    ( 7 )

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USING GIT FOR COLLABORATION

Suppose that Alice has started a new project with a Git repository in /home/alice/project, and that Bob, who has a home directory on the same machine, wants to contribute.

Bob begins with:

bob$ git clone /home/alice/project myrepo

This creates a new directory "myrepo" containing a clone of Alice's repository. The clone is on an equal footing with the original project, possessing its own copy of the original project's history.

Bob then makes some changes and commits them:

(edit files) bob$ git commit -a (repeat as necessary)

When he's ready, he tells Alice to pull changes from the repository at /home/bob/myrepo. She does this with:

alice$ cd /home/alice/project alice$ git pull /home/bob/myrepo master

This merges the changes from Bob's "master" branch into Alice's current branch. If Alice has made her own changes in the meantime, then she may need to manually fix any conflicts.

The "pull" command thus performs two operations: it fetches changes from a remote branch, then merges them into the current branch.

Note that in general, Alice would want her local changes committed before initiating this "pull". If Bob's work conflicts with what Alice did since their histories forked, Alice will use her working tree and the index to resolve conflicts, and existing local changes will interfere with the conflict resolution process (Git will still perform the fetch but will refuse to merge — Alice will have to get rid of her local changes in some way and pull again when this happens).

Alice can peek at what Bob did without merging first, using the "fetch" command; this allows Alice to inspect what Bob did, using a special symbol "FETCH_HEAD", in order to determine if he has anything worth pulling, like this:

alice$ git fetch /home/bob/myrepo master alice$ git log -p HEAD..FETCH_HEAD

This operation is safe even if Alice has uncommitted local changes. The range notation "HEAD..FETCH_HEAD" means "show everything that is reachable from the FETCH_HEAD but exclude anything that is reachable from HEAD". Alice already knows everything that leads to her current state (HEAD), and reviews what Bob has in his state (FETCH_HEAD) that she has not seen with this command.

If Alice wants to visualize what Bob did since their histories forked she can issue the following command:

$ gitk HEAD..FETCH_HEAD

This uses the same two-dot range notation we saw earlier with git log.

Alice may want to view what both of them did since they forked. She can use three-dot form instead of the two-dot form:

$ gitk HEAD...FETCH_HEAD

This means "show everything that is reachable from either one, but exclude anything that is reachable from both of them".

Please note that these range notation can be used with both gitk and "git log".

After inspecting what Bob did, if there is nothing urgent, Alice may decide to continue working without pulling from Bob. If Bob's history does have something Alice would immediately need, Alice may choose to stash her work-in-progress first, do a "pull", and then finally unstash her work-in-progress on top of the resulting history.

When you are working in a small closely knit group, it is not unusual to interact with the same repository over and over again. By defining remote repository shorthand, you can make it easier:

alice$ git remote add bob /home/bob/myrepo

With this, Alice can perform the first part of the "pull" operation alone using the git fetch command without merging them with her own branch, using:

alice$ git fetch bob

Unlike the longhand form, when Alice fetches from Bob using a remote repository shorthand set up with git remote, what was fetched is stored in a remote-tracking branch, in this case bob/master. So after this:

alice$ git log -p master..bob/master

shows a list of all the changes that Bob made since he branched from Alice's master branch.

After examining those changes, Alice could merge the changes into her master branch:

alice$ git merge bob/master

This merge can also be done by pulling from her own remote-tracking branch, like this:

alice$ git pull . remotes/bob/master

Note that git pull always merges into the current branch, regardless of what else is given on the command line.

Later, Bob can update his repo with Alice's latest changes using

bob$ git pull

Note that he doesn't need to give the path to Alice's repository; when Bob cloned Alice's repository, Git stored the location of her repository in the repository configuration, and that location is used for pulls:

bob$ git config --get remote.origin.url /home/alice/project

(The complete configuration created by git clone is visible using git config -l, and the git-config(1) man page explains the meaning of each option.)

Git also keeps a pristine copy of Alice's master branch under the name "origin/master":

bob$ git branch -r origin/master

If Bob later decides to work from a different host, he can still perform clones and pulls using the ssh protocol:

bob$ git clone alice.org:/home/alice/project myrepo

Alternatively, Git has a native protocol, or can use http; see git-pull(1) for details.

Git can also be used in a CVS-like mode, with a central repository that various users push changes to; see git-push(1) and gitcvs-migration(7).