Git

1
Git

• The fast version control system

2
Who am I?

• Senior Software Engineer and Code Chameleon with
  SRA International, Inc
• Coding in HTML and ColdFusion since version 2 of
  each (1995 and 1998 respectively).
• Master of Information Technology.
• Maintainer of The Girlie Code Blog at
  http//mikitracey.org
• Can be reached at miki_at_mikitracey.org
• Download this presentation from
  http//www.mikitracey.org (I will put it in a
  direct link in the toolbar)

3
Agenda

• What is git?
• Distributed?
• Why is it different?
• What are its drawbacks?
• What are its benefits?
• Demos

4
What is git?

• Git was created by Linus Torvald around 2005 and
  is based on bitkeeper.
• Git is a distributed version control system (see
  next slide).
• Comparable to CVS, SVN, PVCS, VSS but also wholly
  and entirely different.
• Open source.

5
Distributed?
Most Version Control Systems Linus Vision of Git Reality of Distributed Systems
6
Design Criteria

• Take CVS as an example of what not to do if in
  doubt, make the exact opposite decision. (Torvald
  is quoted saying incredibly rude things about
  both CVS and SVN and in some cases, hes dead
  right, the rest are probably just matters of
  opinion) http//www.youtube.com/watch?v4XpnKHJAok
  8
• Support a distributed, BitKeeper-like workflow
• Very strong safeguards against corruption, either
  accidental or malicious corruption.
• Very high performance.

7
Why is it different?

• Distributed does not require a central
  repository or even network access.
• Fast designed for speed.
• Nearly incorruptible authenticates file
  downloads using cryptographic grade hashes.
• Compatible - uses http, ftp, ssh, rsync or git
  protocol.
• Better merge capability and independent nature
  mean you can actually use it ALONG with another
  version control system.

8
Drawbacks

• Distributed methodology makes it difficult for
  some people to track multiple branches with the
  same/similar name.
• Uses different terminology, sometimes the same
  word for a different thing. (a common problem
  when switching version control systems)
• Extra steps after check-in to actually push to
  central repository.
• These drawbacks can be mitigated with proper
  training.

9
Benefits

• Fast. Orders of magnitude faster than some
  version control systems (tested by mozilla
  results http//weblogs.mozillazine.org/jst/archiv
  es/2006/11/vcs_performance.html)
• Most version control systems get confused the
  second time you merge one branch to another,
  moreso if there has also been a merge from a
  third branch or changes to the branch you are
  merging to, this doesnt happen in git, it uses
  realtime diffs (similar to compare in svn and
  cvs).
• You can use it locally with no central
  repository, or designate one of the developer
  computers as central repository. (huge benefit)

10
More Benefits

• It can be run on a development box, with
  connections from other developers computers
  without a huge performance hit.
• You can use it to push the code live even if your
  live server is not set up as a git repository.
• You can access files based on commit comment.
• Commit comment is required in most git tools.
  (you cant speak for the content of the comment,
  but at least it has to exist)

11
vocabulary

• fetch - allows examination of changes before
  committing locally, but only on files that would
  have conflicts. Similar to cvs synchronize or
  update.
• pull - get the full repository, similar to cvs
  replace
• push - similar to check in, but of whole branch,
  pushes branch to final destination
• checkout - useful for rolling back to a branch,
  tag or commit comment Similar to pulling an old
  version to commit it.

12
More vocabulary

• HEAD - current branch (a change from what most of
  us are used to).
• master - same as CVS HEAD this is the main branch
  
• clone - create a copy of a repository stored
  locally or elsewhere. (similar to initial check
  out in CVS)
• commit - create a 'changeset' or 'revision',
  similar to cvs commit, but NOT to the central
  repository.

13
git workflow

• Fetch or clone (create a copy of the remote
  repository) (compare to cvs check out)
• Modify the files in the local branch
• Stage the files (no cvs comparison)
• Commit the files locally (no cvs comparison)
• Push changes to remote repository (compare to cvs
  commit)

14
How to get git.

• Source code repository http//git-scm.com/downloa
  d
• Windows tools all come with full copy of git
• Cygwin
• tortoiseGit (can interfere with vpns)
• MSYSgit (most recommended)
• eGit for eclipse

15
How to get help with git

• Read That Fabulous Manual http//www.kernel.org/pu
  b/software/scm/git/docs/user-manual.html
• Books http//progit.org/book/ (free)
• Online training https//github.com/training/onlin
  e
• Git user groups online http//old.nabble.com/git-f
  12403.html
• Git mailing lists git-users_at_googlegroups.com

16
Git Hosting

• For projects that do not require FISMA Certified
  and Acredited hosting, you can view a whole list
  of git hosting sites here https//git.wiki.kernel
  .org/index.php/GitHosting

17
Demos

• Speed demo pull the entire git codebase from
  central repository.
• Replace/eGit demo replace current branch with a
  copy of a remote branch.
• Merge demo local.
• Display history/branches. View file list by
  commit comment.