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From Apache Wiki <wikidi...@apache.org>
Subject [Commons Wiki] Update of "UsingGIT" by LucMaisonobe
Date Tue, 06 Jan 2015 21:17:34 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Commons Wiki" for change notification.

The "UsingGIT" page has been changed by LucMaisonobe:
https://wiki.apache.org/commons/UsingGIT

Comment:
Page creation

New page:
= Overview =
Some of the Apache Commons components use [http://git-scm.com/ GIT] Source Code Management
System instead of [http://subversion.apache.org Subversion].

Both systems allow collaborative development and both systems maintain an history of file
changes. There are however several differences.

= Distributed Version Control =
Git is a distributed version control system. This means that instead of a single central repository
holding the full history of project
files and numerous clients connecting to it to check out some versions, Git uses a symetrical
view were everyone connecting to the
repository clones the full history and from then on could (at least theoretically) act as
a new server that another user could clone
and so on. Each repository is created by cloning an ''origin'' repository. Once cloned, the
''origin'' repository is the first
''remote'' repository known to the clone. It is possible to add later on several other ''remote'',
so a complete web of repositories
can be created. Of course, for collaborative development, some policy has to be decided and
modifications made by one user on its own
cloned repository must be ''pushed'' back to a public repository.

At Apache, the policy is that the official reference is the one hold by Apache servers (for
example http://git-wip-us.apache.org/repos/asf/commons-math.git).
Therefore, all users who want to get the latest version known this is were they should point
at to retrieve it,
and developers who have commit access must push their modifications back to this repository
for official publication.

Distributed version control allow some additional features.

A first use case is a user who do not have commit access but would like to contribute something
to the project. This user would clone
the Apache ''origin'' repository on a publicly accessible computer where he would have commit
access, then he would commit his changes
there. Once the features are complete, the user would propose to the project that they import
his changes back to the official
Apache repository. In order to do so, he would make his repository available (even read-only).
Then an Apache committer willing to
review the work would declare this repository as a remote for his own working clone and would
''pull'' the proposed changes. He could
review everything on his computer, and if satisfied could ''push'' the to the Apache ''origin''
repository, as he has write access
to it. In a way, the Apache committer acts here as a proxy for the contributor, and makes
sure everything is good to include.

A second use case is an Apache committer working either on a long experimental stuff not yet
ready for publication or working
without internet access for some time (typically during a business trip). In both cases, the
committer would simply commit
his work on his laptop, using the full features of the source code management system (branches,
version comparisons, commits, ...).
Once the experiment is completed or internet access is recovered, the committer would push
his work from the past few hours, days
or week back to official repository, with all independent commits preserved instead of being
forced to push a big blob representing
a tremendous work all at once, which would be impossible for his peer committers to review.

A third use case is a user who do not have commit access (and don't want to), but needs to
maintain some local changes. This user
would clone the Apache ''origin'' repository on a private computer, use Git on this computer
to manage his local changes, and from
time to time will merge changes from origin into his clone. This user would never push anything
back.

= Git References =

There are numerous references available online for Git. The first one is the official [http://git-scm.com/book/en/
Pro Git book].
An Apache specific page is [https://git-wip-us.apache.org/ here]
There is also a wiki at kernel.org: [https://git.wiki.kernel.org/ Git Wiki Homepage]

= Comparison with subversion commands =

We first list a subversion command, and after that the equivalent git command.

One of the most important difference from a user point of view is that since there is always
one ''local'' repository and
one or several ''remote'' repositories, there is a distinction in git between saving some
work only locally on a private
computer and making it available to other people who see only public remote computers. The
first action is called ''commit'',
and it is therefore completely different from a subversion commit. The second action is called
''push''. The equivalent
to svn commit is therefore a pair of two commands, git commit followed by git push. It is
possible to perform several
git commit without doing any git push, which is impossible to do with subversion.

 * svn checkout <repo-url>
   git clone http://git-wip-us.apache.org/repos/asf/commons-math.git

 * svn diff
   git diff

 * svn update
   git pull

 * svn commit
   git commit, followed by git push

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