Introduction to Git Commands and Concepts

Intro to GitIntro to Git
Carl BrownCarl Brown

SVN has one masterSVN has one master
Nothing happens in subversion-land without checking with theNothing happens in subversion-land without checking with the
master firstmaster first
Clients are second-class denizensClients are second-class denizens
This is SlowThis is Slow
Limits options because of global lockingLimits options because of global locking
Forces Lowest-Common-Demoninator features because mistakes areForces Lowest-Common-Demoninator features because mistakes are
public and fatalpublic and fatal

All GIT repos are equalAll GIT repos are equal
A "master repo" is a policy decision, not a technical oneA "master repo" is a policy decision, not a technical one
Much fasterMuch faster
More feature-richMore feature-rich
Can perform complex operations without locking all other users outCan perform complex operations without locking all other users out
for an extended timefor an extended time
Allows more risk because you can only hurt yourselfAllows more risk because you can only hurt yourself

A "commit"A "commit"
Just a diff file plus someJust a diff file plus some
metadatametadata
Basic unit of work in gitBasic unit of work in git

Commits in git are identifiedCommits in git are identified
by fingerprintby fingerprint
SHA-1 hashSHA-1 hash
If anything in the commitIf anything in the commit
changes, then SHA changes, sochanges, then SHA changes, so
it’s a new commit (Q.E.D.it’s a new commit (Q.E.D.
commits are immutable)commits are immutable)
You can usually use only theYou can usually use only the
first few characters, as long asfirst few characters, as long as
they're uniquethey're unique
Removes need forRemoves need for
authoritative server source forauthoritative server source for
issuing IDsissuing IDs
Identifies corrupted commitsIdentifies corrupted commits

All git commits contain theirAll git commits contain their
parents IDsparents IDs
So you can trace from anySo you can trace from any
commit back to the verycommit back to the very
first commitfirst commit
Changing the order ofChanging the order of
commits isn't possiblecommits isn't possible
without changing thewithout changing the
commit IDscommit IDs
Commits don't know theirCommits don't know their
children though (notchildren though (not
known when they'reknown when they're
created)created)

Branches and tagsBranches and tags
Just pointersJust pointers
If you point at a single commit, youIf you point at a single commit, you
specify the entire history of the commitspecify the entire history of the commit
This makes branching a trivial operationThis makes branching a trivial operation
A single commit can be the HEAD ofA single commit can be the HEAD of
dozens of branchesdozens of branches
Branch early and oftenBranch early and often
Prolific branches allow git merges to beProlific branches allow git merges to be
explicit instead of implicit (like 'svnexplicit instead of implicit (like 'svn
update' is implicit)update' is implicit)
my “foo” branch may point to a differentmy “foo” branch may point to a different
commit than your “foo” branch, but allcommit than your “foo” branch, but all
“foobar” tags have to point to the exact“foobar” tags have to point to the exact
same commitsame commit

““HEAD”HEAD”
The tip commit ofThe tip commit of
whatever branch you’rewhatever branch you’re
currently working with orcurrently working with or
talking abouttalking about
Although you can useAlthough you can use
“HEAD” in any place that“HEAD” in any place that
would normally take awould normally take a
branch name, if it’s in anybranch name, if it’s in any
way ambiguous, even inway ambiguous, even in
your mind, use the branchyour mind, use the branch
name insteadname instead

"origin""origin"
This is a convention in git asThis is a convention in git as
an alias for the repo youran alias for the repo your
repository was cloned fromrepository was cloned from
While this is often theWhile this is often the
organization’s authoritativeorganization’s authoritative
server, it isn’t alwaysserver, it isn’t always
It’s just an alias for a URL in aIt’s just an alias for a URL in a
config fileconfig file
If you clone from Mark, and IIf you clone from Mark, and I
clone from you, then yourclone from you, then your
repo’s “origin” points at Mark’srepo’s “origin” points at Mark’s
repo, but my “origin” points atrepo, but my “origin” points at
your repoyour repo

"master""master"
This a convention in git for aThis a convention in git for a
"trunk" like branch."trunk" like branch.
Some commands may break if itSome commands may break if it
doesn't existdoesn't exist
What you use it for is a policyWhat you use it for is a policy
matter, not a technological onematter, not a technological one
In Studio, origin/master is alwaysIn Studio, origin/master is always
“the thing QA released most“the thing QA released most
recently”recently”
Your local master can be whateverYour local master can be whatever
Pick something that isn’t likely toPick something that isn’t likely to
confuse you, thoughconfuse you, though

““origin master”origin master”
(used in “push” and “pull” commands)(used in “push” and “pull” commands)
(used in “push” and “pull” commands)(used in “push” and “pull” commands)
That tree - way over thereThat tree - way over there
The default branch of theThe default branch of the
repo you cloned fromrepo you cloned from
replace “origin” with anyreplace “origin” with any
repo name and “master”repo name and “master”
with any branch namewith any branch name

““origin/master”origin/master”
(“merge”,“reset” & “branch” commands)(“merge”,“reset” & “branch” commands)
(“merge”,“reset” & “branch” commands)(“merge”,“reset” & “branch” commands)
A pointer to the commitA pointer to the commit
that was the HEAD of thethat was the HEAD of the
default branch of the repodefault branch of the repo
you cloned from AS OFyou cloned from AS OF
THE LAST TIMEYOUTHE LAST TIMEYOU
FETCHED FROM THATFETCHED FROM THAT
REPO.REPO.
A picture of a tree is not aA picture of a tree is not a
treetree

"index""index"
(also called "cache" but really(also called "cache" but really "staging area""staging area"))
))
Place where changes getPlace where changes get
put when you're preparingput when you're preparing
for a commitfor a commit

““working set” orworking set” or
“working directory”“working directory”
““working directory”working directory”
The files in the directoryThe files in the directory
that you are in the processthat you are in the process
of browsing, editing,of browsing, editing,
compiling, running and/orcompiling, running and/or
testingtesting
The set of source codeThe set of source code
files that Windowsfiles that Windows
Explorer displaysExplorer displays

Interacting with otherInteracting with other
reposrepos

Most git commandsMost git commands
affect only youaffect only you
Except for:Except for:
PushPush
PullPull
FetchFetch
CloneClone
(SVN/CVS/etc.)(SVN/CVS/etc.)
Obscure plumbingObscure plumbing

git clonegit clone
Creates a new repositoryCreates a new repository
on your local machineon your local machine
The new repo is a copy ofThe new repo is a copy of
the repository you clonedthe repository you cloned
fromfrom
The alias “origin” isThe alias “origin” is
assigned in your new localassigned in your new local
repo to point to the onerepo to point to the one
you cloned fromyou cloned from

git fetchgit fetch
Gets all changes from remoteGets all changes from remote
reporepo
Puts those changes in yourPuts those changes in your
local repolocal repo
Does not affect your workingDoes not affect your working
tree or staging areatree or staging area
Should not be any way youShould not be any way you
can get a conflict herecan get a conflict here
If there is a conflict, someoneIf there is a conflict, someone
did something unwisedid something unwise

git pullgit pull
'git fetch' plus 'git merge' in one "easier'git fetch' plus 'git merge' in one "easier
to type" command lineto type" command line
I don’t use this, I recommend you don’tI don’t use this, I recommend you don’t
eithereither
NEVER pull without specifying a repoNEVER pull without specifying a repo
and branch, or git will "guess"and branch, or git will "guess"
You wouldn't merge from "whereverYou wouldn't merge from "wherever
the source control software feels like",the source control software feels like",
you shouldn't pull that way eitheryou shouldn't pull that way either
Don’t pull it if you don’t know youDon’t pull it if you don’t know you
want to be stuck with itwant to be stuck with it
prefer “fetch + merge” if you haveprefer “fetch + merge” if you have
changes or “fetch + reset” if you don’tchanges or “fetch + reset” if you don’t

git pushgit push
Take all changes associated with theTake all changes associated with the
specified branch and give thespecified branch and give the
specified remote server any of themspecified remote server any of them
it is missingit is missing
If someone else doesn’t see yourIf someone else doesn’t see your
changes, you forgot to do thischanges, you forgot to do this
Always specify remote alias andAlways specify remote alias and
branchbranch
Like with the "pull" command, youLike with the "pull" command, you
shouldn’t let the software "guess"shouldn’t let the software "guess"
opposite of fetch (NOT the oppositeopposite of fetch (NOT the opposite
of pull)of pull)
never push to a repo that contains anever push to a repo that contains a
working directoryworking directory

Working in your repoWorking in your repo

git addgit add
Puts changes into thePuts changes into the
“staging area”“staging area”

git commitgit commit
puts staged changes intoputs staged changes into
the local repositorythe local repository
I try to do this every timeI try to do this every time
I compileI compile
When in any doubt,When in any doubt,
commit first!commit first!

git statusgit status
Shows changes in yourShows changes in your
working directory andworking directory and
staging areastaging area

git loggit log
Shows you the history ofShows you the history of
where you arewhere you are
Usually, this is the place toUsually, this is the place to
use a GUI instead, thoughuse a GUI instead, though
How did I get here?How did I get here?

git checkoutgit checkout
Put the files in yourPut the files in your
working directory in aworking directory in a
known stateknown state
Almost alwaysAlmost always
corresponding to acorresponding to a
particular local branchparticular local branch
You can use the ‘-b’ flag toYou can use the ‘-b’ flag to
checkout to make a newcheckout to make a new
local branch and switchlocal branch and switch
your working directory toyour working directory to
it at the same timeit at the same time

git branchgit branch
Make a new (local) branchMake a new (local) branch
List existing (local orList existing (local or
cached) branchescached) branches
Delete a (local) branchDelete a (local) branch

git reset /git reset /
git cleangit clean
git cleangit cleanremove changes youremove changes you
(hopefully) don’t want from(hopefully) don’t want from
your wayyour way
puts the working directoryputs the working directory
and/or the staging area back inand/or the staging area back in
a known statea known state
I use this a lot to sync up to aI use this a lot to sync up to a
branch I don’t have changes inbranch I don’t have changes in
This can lose data - BEThis can lose data - BE
CAREFUL!!CAREFUL!!
When in any doubt, commitWhen in any doubt, commit
first!first!

git mergegit merge
merge 2 or more branchesmerge 2 or more branches
uses 3-way mergesuses 3-way merges
works REALLY wellworks REALLY well
any merge info will get lost ifany merge info will get lost if
you push the result to SVNyou push the result to SVN
No tool substitutes for aNo tool substitutes for a
lack of coordination!lack of coordination!
git mergetool helps with thisgit mergetool helps with this

git rebasegit rebase
rearrange commitsrearrange commits
(illustration coming up(illustration coming up
later)later)
do NOT do this ifdo NOT do this if
someone else is sharingsomeone else is sharing
your changesyour changes
do NOT share changes ifdo NOT share changes if
you’re going to do thisyou’re going to do this

git helpgit help
fairly thorough, but oftenfairly thorough, but often
dense documentationdense documentation
Other resources:Other resources:
http://git.or.cz/course/svn.htmlhttp://git.or.cz/course/svn.html
http://utsl.gen.nz/talks/gihttp://utsl.gen.nz/talks/gi
t-svn/intro.htmlt-svn/intro.html

Some things you probablySome things you probably
shouldn’t doshouldn’t do
‘‘git revert’ probablygit revert’ probably
doesn’t do what you thinkdoesn’t do what you think
if you do have to use it,if you do have to use it,
clean up after yourselfclean up after yourself
as soon as you canas soon as you can
git push -fgit push -f
if you think you need toif you think you need to
do this - something baddo this - something bad
hopefully happened.hopefully happened.
Should not be routine.Should not be routine.

Everyday workflowEveryday workflow

Pro Tips and BestPro Tips and Best
PracticesPractices
commit as often as you build/compilecommit as often as you build/compile
a good commit diff, like a good method, should fit on your screena good commit diff, like a good method, should fit on your screen
don’t worry if it’s not good enough (no one can see it until you push)don’t worry if it’s not good enough (no one can see it until you push)
you might want to get back here (the next thing you do might break)you might want to get back here (the next thing you do might break)
you can always squash lateryou can always squash later
push when you would have committed in cvs/svnpush when you would have committed in cvs/svn
only push when you won’t “break the build” or when tests passonly push when you won’t “break the build” or when tests pass
don’t forget to push when you want other people to see your workdon’t forget to push when you want other people to see your work
branch for every complete functional set/bug fix/featurebranch for every complete functional set/bug fix/feature
keeping functionality separate makes life easier laterkeeping functionality separate makes life easier later
feel free to branch retroactively (but not what svn means by that)feel free to branch retroactively (but not what svn means by that)

Simplified Dev WorkflowSimplified Dev Workflow
(For Larger Teams)(For Larger Teams)
(For Larger Teams)(For Larger Teams)
Get latestGet latest
git fetch origingit fetch origin
Create a new branch for each bug or featureCreate a new branch for each bug or feature
git checkout -b ${feature} origin/${oldbranch}git checkout -b ${feature} origin/${oldbranch}
Make your changes as beforeMake your changes as before
(hopefully committing more often)(hopefully committing more often)
Check inYour Changes LocallyCheck inYour Changes Locally
git commit -am “An Intelligent Comment”git commit -am “An Intelligent Comment”
Push changes back where others can find themPush changes back where others can find them
git push origin ${feature}git push origin ${feature}
Later, merge feature branches together to make Release CandidatesLater, merge feature branches together to make Release Candidates

Making ReleaseMaking Release
Candidate BranchesCandidate Branches

Three Different CombiningThree Different Combining
OptionsOptions
MergeMerge
Keeps HistoryKeeps History
Should Use --no-ffShould Use --no-ff
Harder to trace later in logsHarder to trace later in logs
RebaseRebase
Simplifies History in LogsSimplifies History in Logs
Better for things withoutBetter for things without
common recent parentcommon recent parent
Loses some history infoLoses some history info
Cherry-PickCherry-Pick
Just like rebase but for singleJust like rebase but for single
commitscommits

MergingMerging
““git checkout ${destinationgit checkout ${destination
branch}”branch}”
““git merge ${feature branch}”git merge ${feature branch}”
““git mergetool” if conflictsgit mergetool” if conflicts
““git checkout --ours” orgit checkout --ours” or
“git checkout --theirs” if“git checkout --theirs” if
you want to pick oneyou want to pick one
““git merge ${second featuregit merge ${second feature

RebaseRebase
““git checkout ${feature branch}”git checkout ${feature branch}”
““git checkout -b ${new name}”git checkout -b ${new name}”
to copyto copy
““git rebase ${destinationgit rebase ${destination
if you want every commitif you want every commit
back to common point, orback to common point, or
““git rebase --ontogit rebase --onto
${destination branch}${destination branch}
${last commit not to take}${last commit not to take}
${feature branch}”${feature branch}”
If you want a subsetIf you want a subset

Rebasing ExampleRebasing Example
initial stateinitial state
Figures adapted fromFigures adapted from Pro GitPro Git by Scott Chaconby Scott Chacon
C1C1C1C1
mastemaste
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C2C2C2C2 C5C5C5C5 C6C6C6C6
C8C8C8C8 C9C9C9C9serverserverserverserver
clientclientclientclient

git checkout servergit checkout server
git rebase mastergit rebase master Figures adapted fromFigures adapted from Pro GitPro Git by Scott Chaconby Scott Chacon
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mastemaste
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mastemaste
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serverserverserverserver

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mastemaste
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C8C8C8C8 C9C9C9C9
C3’C3’C3’C3’ C4’C4’C4’C4’ C7’C7’C7’C7’

git rebase --onto master server clientgit rebase --onto master server client
C1C1C1C1
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mastemaste
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C8’C8’C8’C8’ C9’C9’C9’C9’

Staying current with SVNStaying current with SVN
git svn fetchgit svn fetch
Doesn’t update workingDoesn’t update working
tree, but gets branchestree, but gets branches
git svn rebasegit svn rebase
puts SVN revision IDs inputs SVN revision IDs in
git commentsgit comments
have to do this to stay inhave to do this to stay in
syncsync
Loses git history, so makeLoses git history, so make
copied branches in git firstcopied branches in git first

Pushing back to SVNPushing back to SVN
git svn dcommitgit svn dcommit
simplest and safest on SVN sidesimplest and safest on SVN side
requires you rebase in latest SVNrequires you rebase in latest SVN
changeschanges
Make a copied branch in git to doMake a copied branch in git to do
this onthis on
May be preceded by “git resetMay be preceded by “git reset
--hard $git_branch”--hard $git_branch”
git svn set-treegit svn set-tree
Overwrites SVN ignorantly (withOverwrites SVN ignorantly (with
extreme prejudice)extreme prejudice)
nuking the site from Orbitnuking the site from Orbit

Introduction to Git Commands and Concepts

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