The document discusses version control systems and Git. It describes some key benefits of Git such as distributed version control which allows everyone to have the full codebase and commit history, easy branching and merging, and the ability to work offline. The document provides examples of basic Git commands like initializing a repository, adding files, and committing changes. It also highlights features like local repositories for fast operations, tagging releases, and tools for debugging like git blame.

1. Git
Reuven M. Lerner • reuven@lerner.co.il
Open Israel Conference
June 30th, 2011

2. Who am I?
• Web developer, software architect,
consultant, lecturer/trainer
• Linux Journal columnist since 1996
• Mostly Ruby on Rails + PostgreSQL, but
also Python, PHP, jQuery, and lots more...
• Git user (and enthusiast) since 2008

3. What is
version control?

4. Time machine
• Return to any point in
a project’s history
• Find out how files,
folders have changed
• Learn which user
made which changes

5. Backup
• Never fear that you’ve
deleted a file — just
rewind the history
• Everything is recorded,
can be undone

6. Maintenance tool
• “Tag” releases
• Who is to blame for a particular bug?
• When did we introduce a particular
problem?
• Deploy specific versions on specific servers

7. Scratchpad
• Try out new ideas
• Experiment with alternative techniques
• Upgrade a library
• Refactor without affecting the “live” code
base

8. Collaboration tool
• Work without fear of
“stomping” on
someone else’s code
• Identify conflicts
between what
developers wrote
• Mix and match teams
for projects

9. Version control is great
• If you’re a programmer and not using
version control, you’re really missing out
• It’s also good for non-programs, such as
configuration files
• If you’re a CTO/team leader/VP R&D and
your people aren’t using version control,
you’re inviting disaster

10. What do people use?
• RCS (ancient history)
• CVS (should be ancient history)
• Subversion (“a better CVS”)
• SourceSafe
• Perforce
• lots of other systems

11. Problems with these
• Work requires a server connection
• (You can work, but not commit.)
• Branching and merging is painful and slow
• So no one does it!
• Enforces a particular workflow
• More code, more developers — slower VC

12. Distributed version
control
• Distributed: Everyone is their own server!
• Everyone has a complete commit history
• No single point of failure
• Commit whenever you want (i.e., often)
• Merge when two repositories connect

13. Git
• Linus needed a VCS... so he wrote one!
• Fast
• Accurate
• Distributed
• Massively scalable
• Super flexible

14. Open-source Git users
• Linux kernel
• PostgreSQL
• Ruby language
• Ruby on Rails
• Perl language
• among many, many others

15. Give me details!
• What does Git do that others don’t?
• Why do I claim that Git has changed my
life?

16. Branching & merging
• Branching and merging is both easy and fast
in Git
• I often branch and merge several times in a
given day
• When I used SVN, I would do everything
in my power to avoid branching, because
merges were long and difficult

17. Branching & merging
• Create a branch:
git checkout -b new-branch
• Merge commits from other-branch
git merge other-branch
• Yes, it’s really that easy.
• You don’t even have to change directories!

18. Easy branching
changes everything!
• Every new feature goes in a branch
• Merging becomes easy, fast, and natural
• Side projects are stored, not kept out of
version control for fear of “contamination”
• Commit, commit, commit all of the time, in
an appropriate branch — never lose work!

19. Local repository
is great
• Work without a network connection
• Commits, merges, and switching branches
are nearly instantaneous
• Reports and logs are super-fast
• “Show me all files modified on Tuesday of
last week” produces immediate resultss

20. Create a repository!
/tmp $ cd myapp
/tmp/myapp $ git init
Initialized empty Git repository in /private/tmp/myapp/.git/
master ✗ /tmp/myapp $ git add .
master ✗ /tmp/myapp $ git commit -a -m 'Initial commit'
[master (root-commit) 030c6b6] Initial commit
1 files changed, 1 insertions(+), 0 deletions(-)
create mode 100644 foo
Initial commit
master ✔ /tmp/myapp $

21. Create a repository!
/tmp $ cd myapp
/tmp/myapp $ git init
Initialized empty Git repository in /private/tmp/myapp/.git/
master ✗ /tmp/myapp $ git add .
master ✗ /tmp/myapp $ git commit -a -m 'Initial commit'
[master (root-commit) 030c6b6] Initial commit
1 files changed, 1 insertions(+), 0 deletions(-)
create mode 100644 foo
Initial commit
master ✔ /tmp/myapp $

22. Create a repository!
/tmp $ cd myapp
/tmp/myapp $ git init
Initialized empty Git repository in /private/tmp/myapp/.git/
master ✗ /tmp/myapp $ git add .
master ✗ /tmp/myapp $ git commit -a -m 'Initial commit'
[master (root-commit) 030c6b6] Initial commit
1 files changed, 1 insertions(+), 0 deletions(-)
create mode 100644 foo
Initial commit
master ✔ /tmp/myapp $

23. Create a repository!
/tmp $ cd myapp
/tmp/myapp $ git init
Initialized empty Git repository in /private/tmp/myapp/.git/
master ✗ /tmp/myapp $ git add .
master ✗ /tmp/myapp $ git commit -a -m 'Initial commit'
[master (root-commit) 030c6b6] Initial commit
1 files changed, 1 insertions(+), 0 deletions(-)
create mode 100644 foo
Initial commit
master ✔ /tmp/myapp $

24. Create a repository!
/tmp $ cd myapp
/tmp/myapp $ git init
Initialized empty Git repository in /private/tmp/myapp/.git/
master ✗ /tmp/myapp $ git add .
master ✗ /tmp/myapp $ git commit -a -m 'Initial commit'
[master (root-commit) 030c6b6] Initial commit
1 files changed, 1 insertions(+), 0 deletions(-)
create mode 100644 foo
Initial commit
master ✔ /tmp/myapp $

25. Create a repository!
/tmp $ cd myapp
/tmp/myapp $ git init
Initialized empty Git repository in /private/tmp/myapp/.git/
master ✗ /tmp/myapp $ git add .
master ✗ /tmp/myapp $ git commit -a -m 'Initial commit'
[master (root-commit) 030c6b6] Initial commit
1 files changed, 1 insertions(+), 0 deletions(-)
create mode 100644 foo
Initial commit
master ✔ /tmp/myapp $

26. The result
master ✔ /tmp/myapp $ git log
commit 030c6b691993e0f43d78119d9ff1c9e759120d11
Author: Reuven Lerner <reuven@lerner.co.il>
Date: Thu Jun 30 12:29:29 2011 +0300
I

27. Committing in stages
• You can commit all modified files (“git
commit -a”)
• You can add files to be committed (“git add
foo.rb”) over time
• Using the staging area gives you
tremendous flexibility before committing

28. Remote branches
• A local branch can “track” a remote branch
• Different branches can be on different
servers — and then you can merge across
them
• One possible workflow: Read from one
remote branch, and write to another

29. Integration
• Git is all small Unix commands
• Easily integrated into text editors, IDEs,
cron jobs, monitoring, and system tasks
• Example: Continuous integration servers
• Example: Code-analysis tools
• Also: Front ends to SVN and others!

30. git blame
• Shows the commit, user, and timestamp of
when each line of a file was changed
• Useful when you want to know who broke
the build
• Also useful for deflecting blame from
clients, who think you broke something!

31. a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 29)
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 30) #ifdef WIN32
65e806cb (Bruce Momjian 2010-02-26 02:01:40 +0000 31) #define FD_SETSIZE 1024
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 32) #endif /* ! WIN32 */
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 33)
d08741ea (Tom Lane 2001-02-10 02:31:31 +0000 34) #include "postgres_fe.h"
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 35)
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 36) #include "libpq-fe.h"
a8a198b1 (Itagaki Takahiro 2010-01-06 01:30:03 +0000 37) #include "libpq/pqsignal.h"
3da0dfb4 (Tatsuo Ishii 2009-08-03 15:18:14 +0000 38) #include "portability/instr_time.h"
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 39)
d156e1f8 (Tom Lane 2005-10-07 15:34:17 +0000 40) #include <ctype.h>
d156e1f8 (Tom Lane 2005-10-07 15:34:17 +0000 41)
a8a198b1 (Itagaki Takahiro 2010-01-06 01:30:03 +0000 42) #ifndef WIN32
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 43) #include <sys/time.h>
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 44) #include <unistd.h>
ffda6747 (Tom Lane 2007-09-27 20:39:43 +0000 45) #endif /* ! WIN32 */

32. Commit
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 29)
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 30) #ifdef WIN32
65e806cb (Bruce Momjian 2010-02-26 02:01:40 +0000 31) #define FD_SETSIZE 1024
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 32) #endif /* ! WIN32 */
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 33)
d08741ea (Tom Lane 2001-02-10 02:31:31 +0000 34) #include "postgres_fe.h"
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 35)
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 36) #include "libpq-fe.h"
a8a198b1 (Itagaki Takahiro 2010-01-06 01:30:03 +0000 37) #include "libpq/pqsignal.h"
3da0dfb4 (Tatsuo Ishii 2009-08-03 15:18:14 +0000 38) #include "portability/instr_time.h"
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 39)
d156e1f8 (Tom Lane 2005-10-07 15:34:17 +0000 40) #include <ctype.h>
d156e1f8 (Tom Lane 2005-10-07 15:34:17 +0000 41)
a8a198b1 (Itagaki Takahiro 2010-01-06 01:30:03 +0000 42) #ifndef WIN32
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 43) #include <sys/time.h>
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 44) #include <unistd.h>
ffda6747 (Tom Lane 2007-09-27 20:39:43 +0000 45) #endif /* ! WIN32 */

33. Commit User
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 29)
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 30) #ifdef WIN32
65e806cb (Bruce Momjian 2010-02-26 02:01:40 +0000 31) #define FD_SETSIZE 1024
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 32) #endif /* ! WIN32 */
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 33)
d08741ea (Tom Lane 2001-02-10 02:31:31 +0000 34) #include "postgres_fe.h"
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 35)
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 36) #include "libpq-fe.h"
a8a198b1 (Itagaki Takahiro 2010-01-06 01:30:03 +0000 37) #include "libpq/pqsignal.h"
3da0dfb4 (Tatsuo Ishii 2009-08-03 15:18:14 +0000 38) #include "portability/instr_time.h"
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 39)
d156e1f8 (Tom Lane 2005-10-07 15:34:17 +0000 40) #include <ctype.h>
d156e1f8 (Tom Lane 2005-10-07 15:34:17 +0000 41)
a8a198b1 (Itagaki Takahiro 2010-01-06 01:30:03 +0000 42) #ifndef WIN32
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 43) #include <sys/time.h>
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 44) #include <unistd.h>
ffda6747 (Tom Lane 2007-09-27 20:39:43 +0000 45) #endif /* ! WIN32 */

34. Commit User Timestamp
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 29)
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 30) #ifdef WIN32
65e806cb (Bruce Momjian 2010-02-26 02:01:40 +0000 31) #define FD_SETSIZE 1024
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 32) #endif /* ! WIN32 */
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 33)
d08741ea (Tom Lane 2001-02-10 02:31:31 +0000 34) #include "postgres_fe.h"
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 35)
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 36) #include "libpq-fe.h"
a8a198b1 (Itagaki Takahiro 2010-01-06 01:30:03 +0000 37) #include "libpq/pqsignal.h"
3da0dfb4 (Tatsuo Ishii 2009-08-03 15:18:14 +0000 38) #include "portability/instr_time.h"
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 39)
d156e1f8 (Tom Lane 2005-10-07 15:34:17 +0000 40) #include <ctype.h>
d156e1f8 (Tom Lane 2005-10-07 15:34:17 +0000 41)
a8a198b1 (Itagaki Takahiro 2010-01-06 01:30:03 +0000 42) #ifndef WIN32
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 43) #include <sys/time.h>
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 44) #include <unistd.h>
ffda6747 (Tom Lane 2007-09-27 20:39:43 +0000 45) #endif /* ! WIN32 */

35. Commit User Timestamp Line # and code
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 29)
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 30) #ifdef WIN32
65e806cb (Bruce Momjian 2010-02-26 02:01:40 +0000 31) #define FD_SETSIZE 1024
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 32) #endif /* ! WIN32 */
a23c6415 (Magnus Hagander 2009-07-30 09:28:00 +0000 33)
d08741ea (Tom Lane 2001-02-10 02:31:31 +0000 34) #include "postgres_fe.h"
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 35)
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 36) #include "libpq-fe.h"
a8a198b1 (Itagaki Takahiro 2010-01-06 01:30:03 +0000 37) #include "libpq/pqsignal.h"
3da0dfb4 (Tatsuo Ishii 2009-08-03 15:18:14 +0000 38) #include "portability/instr_time.h"
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 39)
d156e1f8 (Tom Lane 2005-10-07 15:34:17 +0000 40) #include <ctype.h>
d156e1f8 (Tom Lane 2005-10-07 15:34:17 +0000 41)
a8a198b1 (Itagaki Takahiro 2010-01-06 01:30:03 +0000 42) #ifndef WIN32
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 43) #include <sys/time.h>
a765db40 (Tatsuo Ishii 2000-01-15 12:38:09 +0000 44) #include <unistd.h>
ffda6747 (Tom Lane 2007-09-27 20:39:43 +0000 45) #endif /* ! WIN32 */

36. git bisect
• You introduced a bug, but don’t know
where? Git can find it!
• Give two endpoints
• Git does a binary search between them
• For each commit, tell Git whether it is
“good” or “bad”
• This finds the bug very quickly

37. Stash
• Temporary storage space
• Useful if you have done enough work to
keep, but not enough for a commit
• Emergency fixes in the middle of working
on something else
• If you need, put the stash into a new branch
• Oh, you can have multiple stashes

38. Hooks
• Execute arbitrary code when things happen
• Example: Update submodules automatically
• Example: Send e-mail after a commit
• Example: Heroku uses hooks to deploy a
new version of your Web app when you
push to them!

39. Workflows
• Git supports many, many workflows
• Traditional centralized server
• BDFL and users
• BDFL and Lieutenants
• Do what works for you!

40. Traditional
Source: ProGit.org

41. Integration-manager
Source: ProGit.org

42. Large, BDFL
Source: ProGit.org

43. Cherry picking
• You can merge specific
commits, or parts of
commits
• Amazingly powerful

44. Rebase
• An alternative to regular merging
• First merge all external commits, then
replay your changes on top
• Helps to keep you aligned with remote
branches
• Avoids some merge-conflict issues

45. Submodules
• A Git repository can point to other
repositories — submodules
• Break a project into smaller projects
• Git puts the pieces together for you!

46. Amending commits
• Commits are not sacred in Git
• Rather, they are a tool to manage history
• Change, amend, and edit commits
• Yes, this can be dangerous!
• Also avoids hundreds of “fixed typo”
commits in a row...

47. Commercial hosting
• You can host Git repositories on your own
• Want to go commercial? GitHub,
Gitorious, and many others work great
• GitHub is free for open-source projects,
and thus very popular

49. GUIs
• Yes, there are now GUIs for Git
• Windows, Mac, and Unix versions all exist
• Integration with Emacs and other editors
for hard-core hacker-nerds
• Also: Shell-prompt integration for Unix

50. In short
• Git has completely changed how I develop
code, both alone and with others
• The speed and easy branching/merging are
game-changers
• It’s really not that hard to start using...
• ... and once you start, you’ll never want to
go back to CVS or SVN

51. Want to learn more?
• Mailing lists, wikis, and blogs
• http://git-scm.com/
• http://progit.org/
• http://gitimmersion.com/
• I’m probably going to offer Git training
soon — let me know if you’re interested!

52. Thanks!
(Any questions?)
reuven@lerner.co.il
http://www.lerner.co.il/
054-496-8405
“reuvenlerner” on Skype/AIM