ASimpleIntroductiontoGit:adistributedversion-controlsystem

CS5010ProgramDesignParadigms“Bootcamp”Lesson0.5

©MitchellWand,2012-2014ThisworkislicensedunderaCreative Commons Attribution-NonCommercial 4.0 International License. 1

LearningObjectives

• Attheendofthislessonyoushouldbeabletoexplain:– howgit createsamini-filesystem inyourdirectory– whatcommit,push,pull,andsyncdo– theelementsofthebasicgit workflow– howgit allowsyoutoworkacrossmultiplecomputers

– howgit allowsyouandapartnertoworktogether

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Git isadistributed version-controlsystem

• Youkeepyourfilesinarepository onyourlocalmachine.

• Yousynchronizeyourrepositorywitharepositoryonaserver.

• Ifyoumovefromonemachinetoanother,youcanpickupthechangesbysynchronizingwiththeserver.

• Ifyourpartneruploadssomechangestoyourfiles,youcanpickthoseupbysynchronizingwiththeserver.

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Git isadistributedversion-controlsystem

• Terminology:Ingit-speak,a“version”iscalleda“commit.”

• Git keepstrackofthehistoryofyourcommits,soyoucangobackandlookatearlierversions,orjustgiveuponthecurrentversionandgobacksomeearlierversion.

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Asimplemodelofgit

• Mostgit documentationgetsintodetailsveryquickly.

• Here’saverysimplemodelofwhat’sgoingoningit.

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Yourfiles

my-project docs manual.docx

user_docs.docx

srcmain.rkt

module1.rkt

module2.rkt

module3.rkt

Hereareyourfiles, sittinginadirectorycalledmy-

project

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Yourfilesinyourgit repository

my-project docs manual.docx

user_docs.docx

srcmain.rkt

module1.rkt

module2.rkt

module3.rkt

.git

Whenyouhaveagit repository,youhaveanadditionaldirectorycalled.git,whichpointsatamini-filesystem.

Thisfilesystemkeepsallyourdata,plusthebellsandwhistlesthatgit needstodoitsjob.

Allthissitsonyourlocalmachine.

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Thegit client

my-project docs manual.docx

user_docs.docx

srcmain.rkt

module1.rkt

module2.rkt

module3.rkt

.git

Thismini-filesystem ishighlyoptimizedandverycomplicated.Don’ttrytoreaditdirectly.

Thejobofthegit client(eitherGithub forWindows,Github forMac,orasuiteofcommand-lineutilities)istomanagethisforyou.

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Yourworkflow(part1)

• Youedityourlocalfilesdirectly.– Youcanedit,addfiles,deletefiles,etc.,usingwhatevertoolsyoulike.

– Thisdoesn’tchangethemini-filesystem,sonowyourmini-fs isbehind.

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ACommit

my-project docs manual.docx

user_docs.docx

srcmain.rkt

module1.rkt

module2.rkt

module3.rkt

.git

commit

Whenyoudoa“commit”,yourecordallyourlocalchangesintothemini-fs.

Themini-fs is“append-only”.Nothing iseverover-writtenthere,soeverythingyouevercommitcanberecovered.

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Synchronizingwiththeserver(1)

my-project docs manual.docx

user_docs.docx

srcmain.rkt

module1.rkt

module2.rkt

module3.rkt

.git push

Attheendofeachworksession,youneedtosaveyourchangesontheserver.Thisiscalleda“push”.

Nowallyourdataisbackedup.• Youcanretrieveit,onyourmachineor

someothermachine.• Wecanretrieveit(that’showwecollect

homework)

yourlocalmachine aserver,somewhereontheinternet,eg.github.com

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Synchronizingwiththeserver(2)

my-project docs manual.docx

user_docs.docx

srcmain.rkt

module1.rkt

module2.rkt

module3.rkt

.git pull

Toretrieveyourdatafromtheserver,youdoa“pull”.A“pull”takesthedatafromtheserverandputsitboth inyour localmini-fsandinyourordinary files.

Ifyourlocalfilehaschanged,git willmergethechangesifpossible.Ifitcan’tfigureouthowtothemerge,youwillgetanerrormessage.We'lllearnhowtodealwiththeseinthenextlesson.

yourlocalmachine aserver,somewhereontheinternet,eg.github.com

pull

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Thewholepicture

my-project docs manual.docx

user_docs.docx

srcmain.rkt

module1.rkt

module2.rkt

module3.rkt

.gitpull

yourlocalmachine aserver,somewhereontheinternet,eg.github.ccs.neu.edu

pull

commit

push

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ThewholepictureusingGHFW

my-project docs manual.docx

user_docs.docx

srcmain.rkt

module1.rkt

module2.rkt

module3.rkt

.git

yourlocalmachine aserver,somewhereontheinternet,eg.github.ccs.neu.edu

sync

commit

InGihub ForWindowsorGithub ForMac,“push”and“pull”arecombined intoasingleoperationcalled“sync”.Sointheseclients,thereareonly twosteps(“commit”and“sync”)toworryabout,notthree.

sync

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Yourworkflow(2)sync

edit

commit

edit

commit

edit

commit

sync

Bestpractice:commityourworkwheneveryou’vegottenonepartofyourproblemworking, orbeforetryingsomething thatmightfail.

Ifyournewstuffisscrewedup,youcanalways“revert”toyour lastgoodcommit.(Remember:always“revert”,never“rollback”)

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UsingGithub forWindows/Mac

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Yourworkflowwithapartner

sync

edit

commit

edit

commit

edit

commit

sync

sync

edit

commit

edit

commit

edit

commit

sync

sync

edit

commit

edit

commit

edit

commit

sync

You You

YourPartner(oryouonanothercomputer)

Yourpartnergetsyourworkfromtheserver

Yougetyourpartner’sworkfromtheserver

server server

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Thenewgithub desktop

• Inthenextfewslides,we’llgiveyoutheupdatesfor2015.

• Wewon’tbeusinggithub.com.Insteadwewillbeusing“Github forEnterprise”athttps://github.ccs.neu.edu

• TheuserinterfaceforGHFW/GHFMhaschanged.It’snowcalled“Github Desktop”.

• Inthenextfewslides,we’llshowyouhowyourdailyworkflowlookswithnewinterface.

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Startingyourworksession• Here’swhatyourGithub Desktopshouldlooklikewhenyou

openitup.Observethatyourreposwillbeinthesectionlabeled“Enterprise”.

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WhereamI?• Theopenbluecircleindicatesthatyouarelookingatthemost

recentlocalfiles

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Alwaysstartbysyncing• Thiswilldownloadanychangesthatyouoryourpartnerhave

madeonothermachines

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Clickonadottoseeacommit• Clickingonthelastdotwillshowyouwhatwasinyourlast

commit• Thedotturnsblue

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• Inthisview,youcanseethefirst6charactersoftheuniqueidentifier(“theSHA”)forthiscommit

• You’llneeditforyourWorksession Report

ThisshowsyourcommitSHA

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Nowlet’sworkonourfile• Nowthescreenshowsanuncommittedchange.

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• Wewriteacommitmessage.Thenwe’llclickon“CommittoMaster”

Next,wecommitourwork

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• Nowitsays“Nouncommittedchanges”again.• Youcanalsoundothecommitifyouwant.

Here’swhatyou’llseeafteracommit

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• Clickontheopencircletoseewhatwasinyourcommit,andtorecordthecommitSHA.Here’sthatscreenagain:

BesuretorecordthecommitSHA

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• Yourworkisnotsavedontheserveruntilyousync.

Besuretosync!!!

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SubmitaWorkSessionReport• Attheendofyourwork

session,submitaworksessionreportviatheweb.

• TheURLfortheworksessionreportwillappearineachproblemset.

• ThereportwillaskfortheSHAofyourlastcommit.YoucangetthisfromtheGithub Desktop,aswe’veshownyou.

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Summary

• Inthislessonyouhavelearned– thatgit createsamini-filesystem inyourdirectory– whatcommit,push,pull,andsyncdo– theelementsofthebasicgit workflow– howgit allowsyoutoworkacrossmultiplecomputers

– howgit allowsyouandapartnertoworktogether

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