1.1

1.2

1.2.1

1.2.2

1.2.3

1.3

1.3.1

1.3.2

1.3.3

1.3.4

1.3.5

1.3.6

1.3.7

1.3.8

1.4

1.4.1

1.4.2

1.5

1.5.1

1.5.2

1.5.3

1.5.4

1.5.5

1.5.6

1.5.7

1.5.8

1.6

1.6.1

1.6.2

1.6.3

1.6.4

1.6.5

1.7

TableofContentsIntroduction

GettingStarted

GettingReadyforClass

GettingStarted

GitHubFlow

Project1:CaptionThis

BranchingwithGit

LocalGitConfigs

WorkingLocally

CollaboratingonCode

EditingonGitHub

MergingPullRequests

LocalHistory

StreamlineWorkflowwithAliases

Project2:MergeConflicts

Definingamergeconflict

ResolvingmergeConflicts

Project3:GitHubGames

WorkflowReview

ProtectedBranches&CODEOWNERS

GitBisect

RevertingCommits

HelpfulGitCommands

ViewingLocalChanges

Tags&Releases

WorkflowDiscussion

Project4:LocalRepository

CreateaLocalRepo

FixingCommitMistakes

RewritingHistorywithGitReset

CherryPicking

MergeStrategies

Appendix

2

3

WelcometoGitHubTodayyouwillembarkonanexcitingnewadventure:learninghowtouseGitandGitHub.

Aswemovethroughtoday'smaterials,pleasekeepinmind:thisclassisforyou!Besuretofollowalong,trytheactivities,andasklotsofquestions!

License

Theprose,coursetext,slidelayouts,classoutlines,diagrams,HTML,CSS,andMarkdowncodeinthesetofeducationalmaterialslocatedinthisrepositoryarelicensedasCCBY4.0.TheOctocat,GitHublogoandotheralready-copyrightedandalready-reservedtrademarksandimagesarenotcoveredbythislicense.

Formoreinformation,visit:http://creativecommons.org/licenses/by/4.0/

Introduction

4

GettingReadyforClassWhileyouarewaitingforclasstobegin,pleasetakeafewminutestosetupyourlocalworkenvironment.

Step1:SetUpYourGitHub.comAccount

Forthisclass,wewilluseapublicaccountonGitHub.com.Wedothisforafewreasons:

Wedon'twantyouto"practice"inrepositoriesthatcontainrealcode.Wearegoingtobreaksomethingssowecanteachyouhowtofixthem.(therefore,refertothebulletabove)

Youcansetupyourfreeaccountbyfollowingthesesteps:

1. AccessGitHub.comandclickSignup.2. Choosethefreeaccount.3. Youwillreceiveaverificationemailattheaddressprovided.4. Clickthelinktocompletetheverificationprocess.

Ifyoualreadyhaveanaccount,verifythatyoucanvisitgithub.comwithinyourorganization'snetwork.

GitHubisdesignedtorunonthecurrentversionsofallmajorbrowsers.Inparticular,ifyouuseMicrosoft'sInternetExplorer(IE),youmustbeusingthelatestversion.Takealookatourlistofsupportedbrowsers.

Step2:InstallGit

Gitisanopensourceversioncontrolapplication.YouwillneedGitinstalledforthisclass.

YoumayalreadyhaveGitinstalledsolet'scheck!OpenTerminalifyouareonaMac,orPowerShellifyouareonaWindowsmachine,andtype:

$git--version

Youshouldseesomethinglikethis:

$git--version

gitversion2.11.0

Anythingover2.0willworkforthisclass!

DownloadingandInstallingGit

Ifyoudon'talreadyhaveGitinstalled,youcandownloadGitatwww.git-scm.com.

IfyouneedadditionalassistanceinstallingGit,youcanfindmoreinformationintheProGitchapteroninstallingGit:http://git-scm.com/book/en/v2/Getting-Started-Installing-Git.

WhereisYourShell?

NowisagoodtimetocreateashortcuttothecommandlineapplicationyouwillwanttousewithGit:

IfyouareworkingonWindows,werecommendGitBashwhichisinstalledwiththeGitpackage,sothatyoucanfollowalongwiththefacilitatorwhowillbeusingBash.IfyouareworkingonaMacorotherUnix-basedsystem,youcanusethebuilt-inTerminalapplication.

GettingReadyforClass

5

Step3:TrycloningwithHTTPS

Openyourchosenshell,andtype:

gitclonehttps://github.com/githubschool/scratch

Ifthecloneissuccessfulyou'llsee:

$gitclonehttps://github.com/githubschool/scratch

Cloninginto'scratch'...

remote:Countingobjects:6,done.

remote:Compressingobjects:100%(2/2),done.

remote:Total6(delta0),reused0(delta0),pack-reused0

Unpackingobjects:100%(6/6),done.

Ifyourcloneisunsuccessful,readaboutauthenticatingwithGitHubfromGit.Pleasenote:manycorporatenetworksrestrictSSHtraffic,sowehighlyrecommendusingHTTPSandverifyingthecloneworksbeforeclass.Also,ifyouhavetwo-factorauthenticationenabledandwishtouseHTTPS,youwillneedtosetupapersonalaccesstoken.

Proxyconfiguration

Ifyourorganizationusesaproxy,youwillneedtoconfiguretheproxysettingsinGit.OpenGitBash(onWindows)orTerminal(onMacor*nix)andcompletetheappropriatestepsbelow:

Ifyourproxydoesnotrequireauthentication:

gitconfig--globalhttp.proxyhttps://YOUR.PROXY.SERVER:8080

ReplaceYOUR.PROXY.SERVERwithyourproxy'sURL.

Ifyourproxydoesrequireauthentication:

gitconfig--globalhttp.proxyhttps://YOUR_PROXY_USERNAME:YOUR_PROXY_PASSWORD@YOUR.PROXY.SERVER:8080

ReplaceYOUR_PROXY_USERNAMEwiththeusernameusedtoauthenticateintoyourproxy,YOUR_PROXY_PASSWORDwiththepasswordusedtoauthenticateintoyourproxy,andYOUR.PROXY.SERVERwithyourproxy'sURL.

Step4:SetUpYourTextEditor

Forthisclass,wewilluseabasictexteditortointeractwithourcode.Let'smakesureyouhaveoneinstalledandreadytoworkfromthecommandline.

PickYourEditor

Youcanusealmostanytexteditor,butwehavethebestsuccesswiththefollowing:

AtomVisualStudioCodeNotepadViorVimSublimeNotepad++GitPad

GettingReadyforClass

6

Ifyoudonotalreadyhaveatexteditorinstalled,goaheadanddownloadandinstalloneoftheaboveeditorsnow!YoucanalsoconfigureAtomasyourdefaulttexteditorforGitcommandsusingtheinstructionsathelp.github.com.

YourEditorontheCommandLine

Afteryouhaveinstalledaneditor,confirmyoucanopenitfromthecommandline.

Ifinstalledproperly,thefollowingcommandwillopentheAtomtexteditor:

$atom.

IfyouareworkingonaMac,youwillneedtoInstallShellCommandsfromtheAtommenu,thishappensaspartoftheinstallationprocessforWindows.

Exploring

Congratulations!YoushouldnowhaveaworkingversionofGitandatexteditoronyoursystem.Ifyoustillhavesometimebeforeclassbegins,herearesomeinterestingresourcesyoucancheckout:

github.com/exploreExploreisashowcaseofinterestingprojectsintheGitHubUniverse.Seesomethingyouwanttore-visit?Startherepositorytomakeiteasiertofindlater.lab.github.comTheLearningLabbotwillguideyouthroughprojectsandprovidefeedbackrightfromyourGitHubrepository,helpingyoubuildeverystepoftheway.

GettingReadyforClass

7

GettingStartedWithCollaborationWewillstartbyintroducingyoutoGit,GitHub,andthecollaborationfeatureswewillusethroughouttheclass.EvenifyouhaveusedGitHubinthepast,wehopethisinformationwillprovideabaselineunderstandingofhowtouseittobuildbettersoftware!

WhatisGitHub?

GitHubisacollaborationplatformbuiltontopofadistributedversioncontrolsystemcalledGit.GitHubisfocusedondevelopers,thepeoplewhocodeandcreatesoftware.Ourfocusisalsothepeoplewhopartnerwithandemploydevelopers,whoareencouragingthemtobuildamazingthings.

Wedoallwecantohelpunlockthecreativityofdevelopersandtofosteracommunityofdevelopersthatcancometogether—asindividualsandinteams—tocreatethefutureofsoftwareandmakeadifferenceintheworld.

GitHubconcentratesonthreethings:

Buildingatechnologyplatformthatislikenoother,onwhichdeveloperscancreate,shareandgrowthebestcodepossibleNurturingacommunityfordevelopers;asafeandcollaborativeplacethatfacilitatessharing,amplifiescreativity,andsupportstheprinciplesofopensourceProvidingaccess,openingupacommunityofopportunity,wherenewdeveloperscanbebornandwhereexperienceddeveloperscanhonetheirskillsandexpandtheirknowledge

InadditiontobeingaplacetohostandshareyourGitprojects,GitHubprovidesanumberoffeaturestohelpyouandyourteamcollaboratemoreeffectively.Thesefeaturesinclude:

IssuesPullRequestsProjectsOrganizationsandTeams

GettingStarted

8

TheGitHubEcosystem

Ratherthanforceyouintoa"onesizefitsall"ecosystem,GitHubstrivestobetheplacethatbringsallofyourfavoritetoolstogether.Formoreinformationonintegrations,checkouthttps://github.com/integrations.

Youmayevenfindsomenew,indispensabletoolstohelpwithcontinuousintegration,dependencymanagement,codequalityandmuchmore.

WhatisGit?

Gitis:

adistributedversioncontrolsystemorDVCS.

GettingStarted

9

freeandopensource.designedtohandleeverythingfromsmalltoverylargeprojectswithspeedandefficiency.easytolearnandhasatinyfootprintwithlightningfastperformance.

Gitfeaturescheaplocalbranching,convenientstagingareas,andmultipleworkflows.

AswebegintodiscussGit(andwhatmakesitspecial)itwouldbehelpfulifyoucouldforgeteverythingyouknowaboutotherversioncontrolsystems(VCSs)forjustamoment.GitstoresandthinksaboutinformationverydifferentlythanotherVCSs.

WewilllearnmoreabouthowGitstoresyourcodeaswegothroughthisclass,butthefirstthingyouwillneedtounderstandishowGitworkswithyourcontent.

Snapshots,notDeltas

OneofthefirstideasyouwillneedunderstandisthatGitdoesnotstoreyourinformationasseriesofchanges.InsteadGittakesasnapshotofyourrepositoryatagivenpointintime.Thissnapshotiscalledacommit.

OptimizedforLocalOperations

Gitisoptimizedforlocaloperation.Whenyoucloneacopyofarepositorytoyourlocalmachine,youreceiveacopyoftheentirerepositoryanditshistory.Thismeansyoucanworkontheplane,onthetrain,oranywhereelseyouradventuresfindyou!

BranchesareLightweightandCheap

BranchesareanessentialconceptinGit.

WhenyoucreateanewbranchinGit,youareactuallyjustcreatingapointerthatcorrespondstothemostrecentcommitinalineofwork.Gitkeepsthecommitsforeachbranchseparateuntilyouexplicitlytellittomergethosecommitsintothemainlineofwork.

GitisExplicit

Whichbringsustoourfinalpointfornow;Gitisveryexplicit.Itdoesnotdoanythinguntilyoutellitto.Noauto-savesorauto-syncingwiththeremote,Gitwaitsforyoutotellitwhentotakeasnapshotandwhentosendthatsnapshottotheremote.

ExploringaGitHubRepository

ArepositoryisthemostbasicelementofGitHub.Itiseasiesttoimagineasaproject'sfolder.However,unlikeanordinaryfolderonyourlaptop,aGitHubrepositoryofferssimpleyetpowerfultoolsforcollaboratingwithothers.

Arepositorycontainsalloftheprojectfiles(includingdocumentation),andstoreseachfile'srevisionhistory.Whetheryouarejustcuriousoryouareamajorcontributor,knowingyourwayaroundarepositoryisessential!

GettingStarted

10

UserAccountsvs.OrganizationAccounts

TherearetwoaccounttypesinGitHub,useraccountsandorganizationaccounts.Whiletherearemanydifferencesintheseaccounttypes,oneofthemorenotabledifferencesishowyouhandlepermissions.

UserAccounts

WhenyousignedupforGitHub,youwereautomaticallygivenauseraccount.Permissionsforauseraccountaresimple,youaddpeopleascollaboratorstospecificrepositoriestogivethemfullread-writeaccesstotheproject.

OrganizationAccounts

Organizationaccountsprovidemoregranularcontroloverrepositorypermissions.Inanorganizationaccountyoucreateteamsofpeopleandthengivethoseteamsaccesstospecificrepositories.Permissionscanbeassignedattheteamlevel(e.g,read,write,oradmin).

RepositoryNavigation

Code

Thecodeviewiswhereyouwillfindthefilesincludedintherepository.Thesefilesmaycontaintheprojectcode,documentation,andotherimportantfiles.Wealsocallthisviewtherootoftheproject.AnychangestothesefileswillbetrackedviaGitversioncontrol.

Issues

Issuesareusedtotrackbugsandfeaturerequests.Issuescanbeassignedtospecificteammembersandaredesignedtoencouragediscussionandcollaboration.

GettingStarted

11

PullRequests

APullRequestrepresentsachange,suchasadding,modifying,ordeletingfiles,whichtheauthorwouldliketomaketotherepository.PullRequestshelpyouwritebettersoftwarebyfacilitatingcodereviewandshowingthestatusofanyautomatedtests.

Projects

ProjectsallowyoutovisualizeyourworkwithKanbanstyleboards.Projectscanbecreatedattherepositoryororganizationlevel.

Wiki

WikisinGitHubcanbeusedtocommunicateprojectdetails,displayuserdocumentation,oralmostanythingyourheartdesires.Andofcourse,GitHubhelpsyoukeeptrackoftheeditstoyourWiki!

Pulse

Pulseisyourproject'sdashboard.Itcontainsinformationontheworkthathasbeencompletedandtheworkinprogress.

Graphs

Graphsprovideamoregranularviewintotherepositoryactivity,includingwhohascontributed,whentheworkisbeingdone,andwhohasforkedtherepository.

README.md

TheREADME.mdisaspecialfilethatwerecommendallrepositoriescontain.GitHublooksforthisfileandhelpfullydisplaysitbelowtherepository.TheREADMEshouldexplaintheprojectandpointreaderstohelpfulinformationwithintheproject.

CONTRIBUTING.md

TheCONTRIBUTING.mdisanotherspecialfilethatisusedtodescribetheprocessforcollaboratingontherepository.ThelinktotheCONTRIBUTING.mdfileisshownwhenauserattemptstocreateanewissueorpullrequest.

ISSUE_TEMPLATE.md

TheISSUE_TEMPLATE.md(anditstwinthepullrequesttemplate)areusedtogeneratetemplatedstartertextforyourprojectissues.Anytimesomeoneopensanissue,thecontentinthetemplatewillbepre-populatedintheissuebody.

UsingGitHubIssues

InGitHub,youwilluseissuestorecordanddiscussideas,enhancements,tasks,andbugs.Issuesmakecollaborationeasierby:

Replacingemailforprojectdiscussions,ensuringeveryoneontheteamhasthecompletestory,bothnowandinthefuture.Allowingyoutocross-linktorelatedissuesandpullrequests.Creatingasingle,comprehensiverecordofhowandwhyyoumadecertaindecisions.

GettingStarted

12

Allowingyoutoeasilypulltherightpeopleintoaconversationwith@mentionsandteammentions.

include

UsingMarkdown

GitHubusesasyntaxcalledMarkdowntohelpyouaddbasictextformattingtoIssues,PullRequests,andfileswiththe.mdextension.

CommonlyUsedMarkdownSyntax

#Header

The#indicatesaHeader.#=Header1,##=Header2,etc.

*Listitem

Asingle*or-followedbyaspacewillcreateabulletedlist.

**Bolditem**

Twoasterix**oneithersideofastringwillmakethattextbold.

-[]Checklist

A-followedbyaspaceand[]willcreateahandychecklistinyourissueorpullrequest.

@mention

Whenyou@mentionsomeoneinanissue,theywillreceiveanotification-eveniftheyarenotcurrentlysubscribedtotheissueorwatchingtherepository.

#975

A#followedbythenumberofanissueorpullrequest(withoutaspace)inthesamerepositorywillcreateacross-link.

:smiley:

Toneiseasilylostinwrittencommunication.Tohelp,GitHuballowsyoutodropemojiintoyourcomments.Simplysurroundtheemojiidwith:.

IntroductiontoGitHubPages

GitHubPagesenableyoutohostfree,staticwebpagesdirectlyfromyourGitHubrepositories.SeveraloftheprojectsweuseinclasswilluseGitHubPagesasthedeploymentstrategy.Wewillbarelyscratchthesurfaceinthisclass,butthereareafewthingsyouneedtoknow:

Youcancreatetwotypesofwebsites,auser/organizationsiteoraprojectsite.Wewillbeworkingwithprojectwebsites.Foraprojectsite,GitHubwillonlyservethecontentonaspecificbranch.Dependingonthesettingsforyourrepository,GitHubcanserveyoursitefromamasterorgh-pagesbranch,ora/docsfolderonthemasterbranch.Therenderedsitesforourprojectswillappearatgithubschool.github.io/repo-name.

GettingStarted

13

GettingStarted

14

UnderstandingtheGitHubflowInthissection,wediscussthecollaborativeworkflowenabledbyGitHub.

TheEssentialGitHubWorkflow

TheGitHubflowisalightweightworkflowthatallowsyoutoexperimentwithnewideassafely,withoutfearofcompromisingaproject.

Branchingisakeyconceptyouwillneedtounderstand.EverythinginGitHublivesonabranch.Bydefault,the"blessed"or"canonical"versionofyourprojectlivesonabranchcalledmaster.Thisbranchcanactuallybenamedanything,aswewillseeinafewminutes.

Whenyouarereadytoexperimentwithanewfeatureorfixanissue,youcreateanewbranchoftheproject.Thebranchwilllookexactlylikemasteratfirst,butanychangesyoumakewillonlybereflectedinyourbranch.Suchanewbranchisoftencalleda"feature"branch.

Asyoumakechangestothefileswithintheproject,youwillcommityourchangestothefeaturebranch.

Whenyouarereadytostartadiscussionaboutyourchanges,youwillopenapullrequest.Apullrequestdoesn'tneedtobeaperfectworkofart-itismeanttobeastartingpointthatwillbefurtherrefinedandpolishedthroughtheeffortsoftheprojectteam.

Whenthechangescontainedinthepullrequestareapproved,thefeaturebranchismergedontothemasterbranch.Inthenextsection,youwilllearnhowtoputthisGitHubworkflowintopractice.

Exploring

Herearesomeinterestingthingsyoucancheckoutlater:

guides.github.com/introduction/flow/AninteractivereviewoftheGitHubWorkflow.

GitHubFlow

15

BranchingwithGitThefirststepintheGitHubWorkflowistocreateabranch.Thiswillallowustoexperimentwithnewfeatureswithoutaccidentallyintroducinguntestedchangesonourproductionbranch.

BranchingDefined

Whenyoucreateabranch,youareessentiallycreatinganidenticalcopyoftheprojectatthatpointintime.Thisisn'tthesameascreatingaphysicalcopyondisk.Inthebackground,abranchisjustapointer.

Let'slearnhowyoucancreateanewbranch.

include

Exploring

Herearesomeinterestingthingsyoucancheckoutlater:

https://youtu.be/H5GJfcp3p4QAGitHubTrainingVideoonbranching.

BranchingwithGit

16

LocalGitConfigurationInthissection,wewillprepareyourlocalenvironmenttoworkwithGit.

CheckingYourGitVersion

First,let'sconfirmyourGitInstallation:

$git--version

$gitversion2.11.0

Ifyoudonotseeagitversionlistedorthiscommandreturnsanerror,youmayneedtoinstallGit.

TogetthelatestversionofGit,visitwww.git-scm.com.

GitConfigurationLevels

Gitallowsyoutosetconfigurationoptionsatthreedifferentlevels.

--system

Thesearesystem-wideconfigurations.Theyapplytoallusersonthiscomputer.

--global

LocalGitConfigs

17

Thesearetheuserlevelconfigurations.Theyonlyapplytoyouruseraccount.

--local

Thesearetherepositorylevelconfigurations.Theyonlyapplytothespecificrepositorywheretheyareset.

Thedefaultvalueforgitconfigis--local.

ViewingYourConfigurations

Ifyouwouldliketoseewhichconfigsettingshavebeenaddedautomatically,youcantypegitconfig--list.Thiswillautomaticallyreadfromeachofthethreeconfigfilesandlistthesettingtheycontain.

$gitconfig--list

Youcanalsonarrowthelisttoaspecificconfigurationlevelbyincludingitbeforethelistoption.

$gitconfig--global--list

ConfiguringYourUserNameandEmail

Gitusestheconfigsettingsforyourusernameandemailaddresstogenerateauniquefingerprintforeachofthecommitsyoucreate.Youcan'tcreatecommitswithoutthesesettings:

$gitconfig--globaluser.name"FirstLast"

$gitconfig--globaluser.email"you@email.com"

GitConfigandYourPrivacy

Theinstructionsforthisexerciseusethe--globalflagwhenidentifyingyouruser.nameanduser.emailconfigurationsettings.Ifyouarecurrentlyusingacomputerwithoutaprivate,personalaccount,don'tapplythe--globalflag.Thisway,thesettingswillonlybestoredinourassignmentrepository.Ifyouworkinanotherrepositoryonthissamecomputer,youwillneedtosettheseconfigurationoptionsagain.

Forexample:

gitconfiguser.email"you@email.com"

YournameandemailaddresswillautomaticallybestoredinthecommitsyoumakewithGit.Ifyouwouldlikeyouremailtoremainprivate,GitHuballowsyoutogenerateano-replyemailaddressforyouraccount.ClicktheKeepmyemailaddressprivateintheSettings>Emailssection.Afterenablingthisfeature,youjustneedtoentertheautomaticallygeneratedID+username@users.noreply.github.comwhenconfiguringyouremail.

Forexample:

gitconfig--globaluser.email18249274+githubteacher@users.noreply.github.com

Configuringautocrlf

$//forWindowsusers

$gitconfig--globalcore.autocrlftrue

$//forMacorLinuxusers

$gitconfig--globalcore.autocrlfinput

LocalGitConfigs

18

Differentsystemshandlelineendingsandlinebreaksdifferently.Ifyouopenafilecreatedonanothersystemanddonothavethisconfigoptionset,gitwillthinkyoumadechangestothefilebasedonthewayyoursystemhandlesthistypeoffile.

MemoryTip:autocrlfstandsforautocarriagereturnlinefeed.

LocalGitConfigs

19

WorkingLocallywithGitUsingthecommandline,youcaneasilyintegrateGitintoyourcurrentworkflow.

CreatingaLocalCopyoftherepo

Beforewecanworklocally,wewillneedtocreateacloneoftherepository.

Whenyouclonearepositoryyouarecreatingacopyofeverythinginthatrepository,includingitshistory.ThisisoneofthebenefitsofaDVCSlikegit-ratherthanbeingrequiredtoqueryaslowcentralizedservertoreviewthecommithistory,queriesarerunlocallyandarelightningfast.

Let'sgoaheadandclonetheclassrepositorytoyourlocaldesktop.

1. NavigatetotheCodetaboftheclassrepositoryonGitHub.2. ClickCloneordownload.3. CopythecloneURLtoyourclipboard.4. Openyourcommandlineapplication.5. RetrieveafullcopyoftherepositoryfromGitHub:gitclone<CLONE-URL>6. Oncethecloneiscomplete,cdintothenewdirectorycreatedbythecloneoperation:cd<REPOSITORY-NAME>

OurFavoriteGitcommand:gitstatus

$gitstatus

Onbranchmaster

Yourbranchisup-to-datewith'origin/master'.

nothingtocommit,workingtreeclean

gitstatusisacommandyouwilluseoftentoverifythecurrentstateofyourrepositoryandthefilesitcontains.Rightnow,wecanseethatweareonbranchmaster,everythingisuptodatewithorigin/masterandourworkingtreeisclean.

UsingBrancheslocally

$gitbranch

WorkingLocally

20

Ifyoutypegitbranchyouwillseealistoflocalbranches.

$gitbranch--all

$gitbranch-a

Ifyouwanttoseeallofthebranches,includingtheread-onlycopiesofyourremotebranches,youcanaddthe--alloptionorjust-a.

The--alland-aareactuallysynonymsforthebranchcommand.Gitoftenprovidesaverboseandashortoption.

SwitchingBranches

$gitcheckout<BRANCH-NAME>

Tocheckoutthebranchyoucreatedonline,typegitcheckoutandthenameofyourbranch.Gitwillprovideamessagethatsaysyouhavebeenswitchedtothebranchandithasbeensetuptotrackthesameremotebranchfromorigin.

Youdonotneedtotyperemotes/origininfrontofthebranch-onlythebranchname.Typingremotes/origininfrontofthebranchnamewillputyouinadetachedHEADstate.Wewilllearnmoreaboutthatlater,butfornowjustrememberthisisnotastatewewanttobein.

include

TheTwoStageCommit

Afteryouhavecreatedyourfile,itistimetocreateyourfirstsnapshotoftherepository.Whenworkingfromthecommandline,youwillneedtobefamiliarwiththeideaofthetwostagecommit.

Whenyouworklocally,yourfilesexistinoneoffourstates.Theyareeitheruntracked,modified,staged,orcommitted.

Anuntrackedfileisanewfilethathasneverbeencommitted.

Gittracksthesefiles,andkeepstrackofyourhistorybyorganizingyourfilesandchangesinthreeworkingtrees.TheyareWorking,Staging(alsocalledIndex),andHistory.Whenweareactivelymakingchangestofiles,thisishappeningintheworkingtree.

WorkingLocally

21

Toaddthesefilestoversioncontrol,youwillcreateacollectionoffilesthatrepresentadiscreteunitofwork.Webuildthisunitinthestagingarea.

Whenwearesatisfiedwiththeunitofworkwehaveassembled,wewilltakeasnapshotofeverythinginthestagingarea.Thisiscalledacommit.

WorkingLocally

22

Inordertomakeafilepartoftheversioncontrolleddirectorywewillfirstdoagitaddandthenwewilldoagitcommit.Let'sdoitnow.

1. First,let'scheckthestatusofourworkingtree:gitstatus2. Movethefilefromtheworkingtreetothestagingarea:gitaddmy-file.md3. Let'sseewhathappened:gitstatus4. Nowlet'stakeourfirstsnapshot:gitcommit5. Gitwillopenyourdefaulttexteditortorequestacommitmessage.Simplytypeyourmessageonthetoplineof

thefile.Anylinewithouta#willbeincludedinthecommitmessage.6. Saveandclosethecommitmessage7. Let'stakeanotherlookatourrepositorystatus:gitstatus

Goodcommitmessagesshould:

Beshort.~50charactersisideal.Describethechangeintroducedbythecommit.Tellthestoryofhowyourprojecthasevolved.

WorkingLocally

23

CollaboratingonYourCodeNowthatyouhavemadesomechangesintheprojectlocally,let'slearnhowtopushyourchangesbacktothesharedclassrepositoryforcollaboration.

PushingYourChangestoGitHub

Inthiscase,ourremoteisGitHub.com,butthiscouldalsobeyourcompany'sinternalinstanceofGitHubEnterprise.

TopushyourchangestoGitHub,youwillusethecommand:

$gitpush

Whenyoupush,youwillbeaskedtoenteryourGitHubusernameandpassword.IfyouwouldlikeGittorememberyourcredentialsonthiscomputer,youcancacheyourcredentialsusing:

Windows:gitconfig--globalcredential.helperwincredMac:gitconfig--globalcredential.helperosxkeychain

include

ExploringaPullRequest

NowthatwehavecreatedaPullRequest,let'sexploreafewofthefeaturesthatmakePullRequeststhecenterofcollaboration:

Conversationview

CollaboratingonCode

24

SimilartothediscussionthreadonanIssue,aPullRequestcontainsadiscussionaboutthechangesbeingmadetotherepository.ThisdiscussionisfoundintheConversationtabandalsoincludesarecordofallofthecommitsmadeonthebranchaswellasassignments,labelsandreviewsthathavebeenappliedtothepullrequest.

Commitsview

Thecommitsviewcontainsmoredetailedinformationaboutwhohasmadechangestothefiles.ClickingeachcommitIDwillallowyoutoseethechangesappliedinthatspecificcommit.

Fileschangedview

TheFileschangedviewallowsyoutoseecumulativeeffectofallthechangesmadeonthebranch.Wecallthisthediff.Ourdiffisn'tveryinterestingyet,butaswemakechangesyourdiffwillbecomeverycolorful.

CodeReviewinPullRequests

Toprovidefeedbackonproposedchanges,GitHuboffersthreelevelsofcommenting:

GeneralConversation

YoucanprovidegeneralcommentsonthePullRequestwithintheConversationtab.

LineComments

Inthefileschangedview,youcanhoveroveralinetoseeablue+icon.Clickingthisiconwillallowyoutoenteracommentonaspecificline.Theselinelevelcommentsareagreatwaytogiveadditionalcontextonrecommendedchanges.Theywillalsobedisplayedintheconversationview.

Review

Whenyouaremakinglinecomments,youcanalsochoosetoStartaReview.Whenyoucreateareview,youcangroupmanylinecommentstogetherwithageneralmessage:Comments,Approve,orRequestChanges.ReviewshavespecialpowerinGitHubwhenusedinconjunctionwithprotectedbranches.

Activity:CodeReview

OneofthebestwaystoensurecodequalityistomakepeerreviewsapartofeveryPullRequest.Let'sreviewyourpartner'scodenow:

1. ClickthePullRequesttab.2. UsetheAuthordropdowntolocateyourpartner'spullrequest.3. ClicktheFilesChangedtab.4. Hoveroverasinglelineinthefiletoseetheblue+.Clickthe+toaddalinecomment.5. CommentonthelineandclickStartareview.6. Addadditionallinecommentstothepullrequest.7. ClickReviewchangesinthetoprightcorner.8. ChoosewhethertoApproveorRequestchanges9. Enterageneralcommentforthereview.10. ClickSubmitreview11. ClicktheConversationviewtocheckoutyourcompletedreview.

CollaboratingonCode

25

CollaboratingonCode

26

EditingFilesonGitHubSinceyoucreatedthepullrequest,youwillbenotifiedwhensomeoneaddsacommentorareview.Sometimes,thereviewerwillaskyoutomakeachangetothefileyoujustcreated.Let'sseehowGitHubmakesthiseasy.

EditingaFileonGitHub

Toeditapullrequestfile,youwillneedtoaccesstheFilesChangedview.

1. ClickthepenciliconinthetoprightcornerofthedifftoeditthefileusingtheGitHubfileeditor.2. Makechangestothefilebasedonthecommentsfromyourrevieweroryourpersonalperspective.

CommittingChangesonGitHub

Onceyouhavemadesomechangestoyourfile,youwillneedtocreateanewcommit.

1. ScrolltothebottomofthepagetofindtheCommitchangesdialogbox.2. TypeaCommitmessage.3. ChoosetheoptiontoCommitdirectlytoyourbranch.4. ClickCommitchanges.

Activity:EditingFilesinPullRequests

GobacktoyourPullRequestandmaketheeditsrequestedbyyourcollaborators.

EditingonGitHub

27

MergingPullRequestsNowthatyouhavemadetherequestedchanges,yourpullrequestshouldbereadytomerge.

MergeExplained

Whenyoumergeyourbranch,youaretakingthecontentandhistoryfromyourfeaturebranchandaddingittothecontentandhistoryofthemasterbranch.

Manyprojectteamshaveestablishedrulesaboutwhoshouldmergeapullrequest.

Somesayitshouldbethepersonwhocreatedthepullrequestsincetheywillbetheonestodealwithanyissuesresultingfromthemerge.Otherssayitshouldbeasinglepersonwithintheprojectteamtoensureconsistency.Stillotherssayitcanbeanyoneotherthanthepersonwhocreatedthepullrequesttoensureatleastonereviewhastakenplace.

Thisisadiscussionyoushouldhavewiththeothermembersofyourteam.

MergingYourPullRequest

Let'stakealookathowyoucanmergethepullrequest.

1. NavigatetoyourPullRequest(HINT:UsetheAuthororAssigneedropdownstofindyourPullRequestquickly)2. ClickConversation3. ScrolltothebottomofthePullRequestandclicktheMergepullrequestbutton4. ClickConfirmmerge5. ClickDeletebranch6. ClickIssuesandconfirmyouroriginalissuehasbeenclosed

GitHuboffersthreedifferentmergestrategiesforPullRequests:

Createamergecommit:Thisisthetraditionaloptionthatwillperformastandardrecursivemerge.Anewcommitwillbeaddedthatshowsthepointwhenthetwobranchesweremergedtogether.Squashandmerge:Thisoptionwilltakeallofthecommitsonyourbranchandcompressthemintoasinglecommit.Thecommitmessageswillbepreservedintheextendedcommitmessageforthecommit,buttheindividualcommitswillbelost.Rebaseandmerge:Thisoptionwilltakeallofthecommitsandreplaythemasiftheyjusthappened.ThisallowsGitHubtoperformafastforwardmerge(andavoidstheadditionofthemergecommit).

UpdatingYourLocalRepository

MergingPullRequests

28

WhenyoumergedyourPullRequest,youdeletedthebranchonGitHub,butthiswillnotautomaticallyupdateyourlocalcopyoftherepository.Let'sgobacktoourcommandlineapplicationandgeteverythinginsync.

First,weneedtogetthechangeswemadeonGitHubintoourlocalcopyoftherepository:

1. Startbyswitchingbacktoyourdefaultbranch:gitcheckoutmaster2. RetrieveallofthechangesfromGitHub:gitpull

gitpullisacombinationcommandthatretrievesallofthechangesfromGitHubandthenupdatesthebranchyouarecurrentlyontoincludethechangesfromtheremote.Thetwoseparatecommandsbeingrunaregitfetchandgitmerge

CleaningUptheUnneededBranches

Ifyoutypegitbranch--allyouwillprobablyseethat,eventhoughyoudeletedyourbranchontheremote,itisstilllistedinyourlocalcopyoftherepository,bothasalocalbranchandasaread-onlyremotetrackingbranch.Let'sgetridofthoseextrabranches.

1. Takealookatyourlocalbranches:gitbranch--all2. Let'sseewhichbranchesaresafetodelete:gitbranch--merged3. Deletethelocalbranch:gitbranch-d<branch-name>4. Takeanotherlookatthelist:gitbranch--all5. Yourlocalbranchisgonebuttheremotetrackingbranchisstillthere.Deletetheremotetrackingbranch:git

pull--prune

Addingthe--mergedoptiontothegitbranchcommandallowsyoutoseewhichbranchesdonotcontainuniqueworkwhencomparedtothecheckedoutbranch.Inthiscase,sincewearecheckedouttomaster,wewillusethiscommandtoensureallofthechangesonourfeaturebranchhavebeenmergedtoproductionbeforewedeletethebranch.

Ifyouwouldlikepruningoftheremotetrackingbranchestobesetasyourdefaultbehaviorwhenyoupull,youcanusethefollowingconfigurationoption:gitconfig--globalfetch.prunetrue.

MergingPullRequests

29

ViewingLocalProjectHistoryInthissection,youwilldiscovercommandsforviewingthehistoryofyourproject.

UsingGitLog

Whenyouclonearepository,youreceivethehistoryofallofthecommitsmadeinthatrepository.Thelogcommandallowsustoviewthathistoryonourlocalmachine.

Let'stakealookatsomeoftheoptionswitchesyoucanusetocustomizeyourviewoftheprojecthistory.Youcanfindtheseoptions,andmanymore,ongit-scm.com.(Note:--graphisdefaultonmostGitBashforWindowsterminals.)

$gitlog

$gitlog--oneline

$gitlog--oneline--graph

$gitlog--oneline--graph--decorate

$gitlog--oneline--graph--decorate--all

$gitlog--stat

$gitlog--patch

Usetheupanddownarrowsorpressentertoviewadditionallogentries.Typeqtoquitviewingthelogandreturntothecommandprompt.

LocalHistory

30

StreamliningYourWorkflowwithAliasesSofarwehavelearnedquiteafewcommands.Some,likethelogcommands,canbelongandtedioustotype.Inthissection,youwilllearnhowtocreatecustomshortcutsforGitcommands.

CreatingCustomAliases

Analiasallowsyoutotypeashortenedcommandtorepresentalongstringonthecommandline.

Forexample,let'screateanaliasforthelogcommandwelearnedearlier.

OriginalCommand

$gitlog--oneline--graph--decorate--all

CreatingtheAlias

$gitconfig--globalalias.lol"log--oneline--graph--decorate--all"

UsingtheAlias

$gitlol

ExploreOtherHelpfulAliases

Checkouttheseresourcesforalistofcommonaliases:

git-scm.com/book/en/v2/Git-Basics-Git-AliasesAhelpfuloverviewofsomeofthemostcommongitaliases.

WealsoencourageyoutoreadthroughthesethreeblogpostsbyGitHubdeveloperPhilHack.Histipsarereferencedthroughoutthemanual.

GitHubFlowAliasesGitMigrateGitAliasOpenURL

ProTip#1:Toeditaliasesbyhand,youcanopenthegitconfigfilewithyourdefaulteditor.

gitconfig--globalalias.ec"config--global-e"

ProTip#2:Tocheckouttoanotherbranch,youcanmakeaquickshortcut.

gitconfig--globalalias.ch"checkout"

ProTip#3:Tocheckouttoabrandnewbranch,youcaneasilyextendyourexistingshortcut.

gitconfig--globalalias.cob"checkout-b"

ProTip#4:Youcancreatealiasesthatonlycallonecommand.

gitconfig--globalalias.s"status-s"

StreamlineWorkflowwithAliases

31

ProTip#5:Cleanupbranchesquicklyandeasily.

$gitconfigalias.dlb'!gitcheckout<DEFAULT-BRANCH>&&gitpull--prune&&gitbranch--merged|grep-v"\*

"|xargs-n1gitbranch-d'

StreamlineWorkflowwithAliases

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Whatisamergeconflict?Whenyouworkwithateam(andevensometimeswhenyouareworkingalone)youwilloccasionallycreatemergeconflicts.Atfirst,mergeconflictscanbeintimidating,butresolvingthemisactuallyquiteeasy.Inthissectionyouwilllearnhow!

Theseexerciseswillfocusonthetechnical"how".Inrealmergeconflicts,it'simportanttoknowwhotoaskincaseyouaren'tsurehowtoresolvetheconflictonyourown.Usuallyit'sagoodideatoaskthepersonwhomadetheconflictingchanges,orsomeonewhoisaCODEOWNERonthefile.

LocalMergeConflicts

Mergeconflictsareanaturalandminorsideeffectofdistributedversioncontrol.Theyonlyhappenunderveryspecificcircumstances.

Changestothesame"hunk"ofthesamefileTwodifferentbranchesChangesonbothbrancheshappenedsincethebrancheshavediverged

Definingamergeconflict

33

ResolvingaMergeConflict

Let'strytocreateamergeconflict,andfixittogether.Youandapartnerwilleachcreateseparatebranches,createafilewiththesamename,andthentrytomerge.Thefirstwillmergecleanly,thesecondwillhaveamergeconflict.Worktogethertoresolvethemergeconflict.

1. Inourclassrepository,createthebranchthatyouwillbeworkingonandnameitsomethingmemorablelikeUSERNAME-conflict.

2. Chooseafilethatbothyouandyourpartnerwilledit.(Oneofyourfilesfromearlierwouldworkwell.)Onyourbranch,editthatfile.Thefilenamemustbethesamefilenamethatyourpartneruses.Makesurethecontentinsideofthefileisdifferent,andthatneitherfileisempty.

3. Createapullrequestintheclassrepositorywithbase:masterandcompare:USERNAME-conflict.4. Youwillseethatthefirstpullrequestcanmergewell.5. Whenyouseethemergeconflictinthesecondpullrequest,worktogethertoresolvethemergeconflict.

i. Workinglocally,mergemasterintothefeaturebranch.ii. Whenyouseethere'saconflict,that'sOK!ThefilesthathaveconflictsarelistedunderUnmergedPaths.

Typegitstatustoverifywhichfilehastheconflict.iii. Openthatfileinyourtexteditor,andlookforthemergeconflictmarkers.(<<<<<<<,=======,>>>>>>>)iv. Bothbranches'versionsofcodearepresent-pickwhichoneyouwanttokeep,andsavethechanges.v. Addandcommitthesavedchangestoresolvethemergeconflict.vi. Pushthefeaturebranchuptotheremote,andseetheresolutioninthepullrequest.

6. Mergethepullrequest.

Whatisamergemessage?Inthisexample,wearedoingarecursivemerge.Arecursivemergecreatesanewcommitthatpermanentlyrecordsthepointintimewhenthesetwobranchesweremergedtogether.WewilltalkmoreaboutGit'smergestrategiesalittlelater.

ResolvingmergeConflicts

34

Project:GitHubGamesInthissection,wewillworkonaprojectrepositorycalledgithub-games.

Agithub-gamesrepositoryhasbeencreatedforyouinthegithubschoolorganization.Youcanaccesstherepositoryathttps://github.com/githubschool/github-games-USERNAME.

Ifyou'reusingtheForkandPullWorkflow,don'tforgettolookintheappendixforamorethoroughexplanation.

WorkflowReview:UpdatingtheREADME.md

NowyouwillpracticetheGitHubFlowfrombeginningtoendbyupdatingthelinkintheREADMEtopointtoyourforkoftherepository.

Remember,yourcopyofthewebsitewillberenderedathttps://githubschool.github.io/github-games-USERNAME.

Thislinkalsoappearsintherepositorydescription.ItisagoodideatoeditthewebsiteURLinthedescriptionsoyoucaneasilyaccessyourgame.

Ifyouclickthelink,youwillseethetextintheREADME.md.Wehaveintentionallybrokenthisrepositorysowecanfixittogether.

Sincethisisareview,wehavewrittenthesestepsatahighlevel.Aswecompletethereview,wewillshowyouafewshortcutsforthecommandsyoulearnedinthepreviousactivity:

1. Cloneyourcopyoftherepository:gitclonehttps://github.com/githubschool/github-games-USERNAME.git2. Createanewbranchcalledreadme-update:gitcheckout-breadme-update3. EdittheURLintheREADME.md.4. Committhechangestoyourbranch.5. PushyourbranchtoGitHub:gitpush-uoriginreadme-update6. CreateaPullRequestinyourrepository(base:master,compare:readme-update)7. MergeyourPullRequest.8. DeletethebranchonGitHub.9. Updateyourlocalcopyoftherepository:gitpull--prune

gitcheckout-breadme-updateisashortcutcommandthatallowsyoutocombinethecreationofthebranch(gitbranchreadme-update)andcheckingouttothatbranch(gitcheckoutreadme-update).The-btellsGittocreateanewbranch.

gitpush-uoriginreadme-updateistheslightlylongerversionofthepushcommandthatshouldbeusedwhenyoupushanewbranchforthefirsttime.

The-uistheshortversionoftheoption--set-upstream.ThisoptiontellsGittocreatearelationshipbetweenourlocalbranchandaremotetrackingbranchofthesamename.\

Youonlyneedtousethislongcommandthefirsttimeyoupushanewbranch.Afterthat,youcansimplyusegitpush.

gitconfig--globalalias.bclean"!f(){branches=$(gitbranch--merged${1-master}|grep-v"${1-master}$");[-

z\"$branches\"]||gitbranch-d$branches;};f"couldbehelpfulhere.Takeapeekintheappendixtolearnhow!

WorkflowReview

35

WorkflowReview

36

ProtectedBranches&CODEOWNERSInsomeworkflows,youwillwanttoprotectcriticalbranchestoensurethecodebeingmergedtothosebrancheshaspassedtherequiredchecksandreceivedappropriatepeerreview.Thereareseveralmethodsforthis,includingProtectedBranchesandCodeOwners.

ProtectedBranches

Repositorymaintainerscanpreventmergestospecificbranchesthathavenotmetpre-definedcriteria.Thiscriteriacanincludepeerreviews,testsrunbyintegrationssuchasaContinuousIntegrationservicesorcodequality,oruntilaspecificcodeownerhasreviewedandapprovedchanges.

Let'senableprotectedbranches:

1. SelecttheSettingstab.2. SelectBranchesfromthemenuontheleftsideofthescreen.3. ClicktheAddrulebuttonnexttoBranchprotectionrules.4. IntheApplyruletotextboxtypethenameofthebranchyouwouldliketoprotect,forexample,master.5. ClicktheCreatebutton.

Withoutcheckinganyotheroptions,basicbranchprotectionpreventsforce-pushesandpreventsitfrombeingdeleted.Tolearnmoreabouttheoptionsavailable,checkoutthedocumentationforthisfeature.

Protip:Youcanusewildcards(*,?)andregularexpressionstomakeabranchprotectionruleapplytomultiplebranches.Checkoutthebranchprotectiondocumentationformoreinformationonhowwildcardsandregularexpressionmatchingwork.

CODEOWNERS

RepositorymaintainerscandefineexactlywhichpeopleandteamsneedtoreviewsetsofchangesbycreatingaCODEOWNERSfile.Forexample,youcoulduseCODEOWNERStoensure:

yourteam'sJavascriptexpertreviewsallfileswitha.jsextensionyourtechnicaldocumentationteamreviewsallchangesinthedocs/folderyoursecurityteamreviewsanynewdependencieslistedinthepackage.jsonfile

Let'screateaCODEOWNERSfile:

1. GoouttotheCodetabofyourrepository.2. ClicktheCreatenewfilebutton.3. IntheNameyourfile...textboxenterCODEOWNERS(noextensionnecessary).Youcanaddthistoa.github/

directoryifdesiredbyentering.github/CODEOWNERS.4. Onthefirstline,type*@YOUR_USERNAME

Thismeansthatyouwillbethedefaultownerforeverythingintherepo,unlessalatermatchtakespreference.

5. Onthenextline,type*.js@GITHUBTEACHEROrderisimportant.Thelastmatchingpatternforagivenchangetakesprecedence.

6. Scrolldown,andtypeacommitmessageintotheCommitnewfiledialogbox.7. ClicktheCommitnewfilebuttontosaveyourchanges.8. NowthatyouhavecreatedaCODEOWNERSfile,gobacktoyourbranchprotectionsettingsandclicktheEdit

buttonnexttomaster.9. UnderRulesettings,selecttheoptiontoRequirepullrequestreviewsbeforemergingandRequirereview

fromCodeOwners.RemembertoclickSavechanges.

ProtectedBranches&CODEOWNERS

37

FormoreinformationonhowtoformattheCODEOWNERSfile,checkoutthedocumentation

ProtectedBranches&CODEOWNERS

38

SearchingforEventsinYourCodeInthissection,wewilllearnhowwecanusegitbisecttofindthecommitthatintroducedabugintoourrepository.

Whatisgitbisect?

Usingabinarysearch,gitbisectcanhelpusdetectspecificeventsinourcode.Forexample,youcouldusebisecttolocatethecommitwhere:

abugwasintroduced.anewfeaturewasadded.abenchmark’sperformanceimproved.

Howitworks

gitbisectworksbycuttingthehistorybetweentwopointsinhalfandthencheckingyououttothatcommit.Youthencheckwhetherthebug/featureexistsatthatpointandtellGittheresult.Fromthere,Gitwilldoanotherdivision,etcuntilyouhavelocatedthedesiredcommit.

Whenyouaredoingabisect,youareessentiallyinadetachedheadstate.ItisimportanttoremembertoendthebisectwithgitbisectresetbeforeattemptingtoperformotheroperationswithGit.

FindingtheBuginOurProject

TheLongWay

1. Initiatethebinarysearch:gitbisectstart.2. Specifythecommitwhereyounoticedthecodewasbroken:gitbisectbad<SHA>.3. Specifythecommitwhereyouknewthingswereworking:gitbisectgood<SHA>.4. Bisectwillcheckyououttothemidpointbetweengoodandbad.5. Runatesttoseeifthegamewouldworkatthispoint.Ourtestistouselstoseeifanindex.htmlfileexists.

GitBisect

39

6. Ifthegameisstillbroken(thereisnoindex.htmlfile),type:gitbisectbad.7. Ifthegameworks(andthereisanindex.htmlfile),type:gitbisectgood.8. Gitwillbisectagainandwaitforyoutotest.ThiswillhappenuntilGithasenoughinformationtopinpointthefirst

badcommit.9. WhenGithasdetectedtheerror,itwillprovideamessagethatSHAisthefirstbadcommit.10. Exitthebisectprocess:gitbisectreset.

TheShortWay

Bisectcanalsorunthetestsonyourcodeautomatically.Let'stryitagainusingashortcutcommandandatest:

1. gitbisectstart<bad-SHA><good-SHA>2. gitbisectrunlsindex.html3. gitbisectreset

GitBisect

40

RevertingCommitsInthissection,wewilllearnaboutcommandsthatre-writehistoryandunderstandwhenyoushouldorshouldn'tusethem.

HowCommitsAreMade

EverycommitinGitisauniquesnapshotoftheprojectatthatpointintime.Itcontainsthefollowinginformation:

PointerstothecurrentobjectsintherepositoryCommitauthorandemail(fromyourconfigsettings)CommitdateandtimeCommitmessage

EachcommitalsocontainsthecommitIDofitsparentcommit.

Imagesource:ProGitv2byScottChacon

SafeOperations

Git'sdatastructuregivesitintegritybutitsdistributednaturealsorequiresustobeawareofhowcertainoperationswillimpactthecommitsthathavealreadybeenshared.

RevertingCommits

41

IfanoperationwillchangeacommitIDthathasbeenpushedtotheremote(alsoknownasapubliccommit),wemustbecarefulinchoosingtheoperationstoperform.

GuidelinesforCommonCommands

Command Cautions

revert Generallysafesinceitcreatesanewcommit.

commit--amend Onlyuseonlocalcommits.

reset Onlyuseonlocalcommits.

cherry-pick Onlyuseonlocalcommits.

rebase Onlyuseonlocalcommits.

RevertingCommits

Togetyourgameworking,youwillneedtoreversethecommitthatincorrectlyrenamesindex.html.

Warning:Beforeyoureversethecommit,itisagoodideatomakesureyouwillnotbeinadvertentlyreversingotherchangesthatwerelumpedintothesamecommit.Toseewhatwaschangedinthecommit,usegitshowSHA.

1. Initializetherevert:gitrevert<SHA>2. Typeacommitmessage.3. PushyourchangestoGitHub.

RevertingCommits

42

HelpfulGitCommandsInthissection,wewillexploresomehelpfulGitcommands.

MovingandRenamingFileswithGit

1. Createanewbranchnamedslow-down.2. Online9oftheindex.htmlfile,changethebackgroundurlto(images/texture.jpg).3. Online78,changethetimingforthegametospeedituporslowitdown.4. Saveyourchanges.5. Seewhatgitistracking:gitstatus6. Createanew,emptydirectory:mkdirimages7. Movethetexturefileintothedirectorywithgit:gitmvtexture.jpgimages/texture.jpg

StagingHunksofChanges

Craftingatomiccommitsisanimportantpartofcreatingareadableandinformativehistoryoftheproject.

1. Seewhatgitistracking:gitstatus.2. Movesomepartsofsomefilestothestagingareawiththe--patchflag:gitadd-p.3. Stagethehunkrelatedtotheimagemove:y4. Leavethehunkrelatedtothespeedchangeintheworkingarea:n

Wonderingwhatallofthoseotheroptionsareforthehunks?Usethe?toseealistofoptionsabovethehunk.

gitconfig--globalalias.cm"!gitadd-A&&gitcommit-m"couldbehelpfulhere.Checkouttheappendixtoseehow!

HelpfulGitCommands

43

ViewingLocalChangesNowthatyouhavesomefilesinthestagingareaandtheworkingdirectory,let'sexplorehowyoucancomparedifferentpointsinyourrepository.

ComparingChangeswithintheRepository

gitdiffallowsyoutoseethedifferencebetweenanytworefsintherepository.Thediagrambelowshowshowyoucancomparethecontentofyourworkingarea,staging,andHEAD(orthemostrecentcommit):

Let'strythesecommandsontherepository:

$gitdiff

$gitdiff--staged

$gitdiffHEAD

$gitdiff--color-words

gitdiffwillalsoallowyoutocomparebetweenbranches,commits,andtagsbysimplytyping:

$gitdiff<REF-1><REF-2>

$gitdiffmasterslow-down

$gitdifforigin/mastermaster

$gitdiff2710b745

Noticethat,justlikemerges,diffsaredirectional.Itiseasiesttothinkofitas"diffbackto<REF-1>startingat<REF-2>"or"seewhatisnotin<REF-1>butisin<REF-2>".Thefinalexampleshowshowtocomparetwocommitsbasedontheircommithashes.Thisexactcommandwillnotworkforeveryonesincethecommitsinyourownrepositorywillhavedifferenthashes.

There'sahelpfulaliasforopeningtheremotedirectlyfromyourcommandline.Checkouttheappendixifyou'dliketoknowmore!

ViewingLocalChanges

44

ViewingLocalChanges

45

TagsandReleasesYoumaywanttoputtagsorreleasesoncertaincommitsinyourcode'shistorytomarkspecificstatesorplacesintime.Todothis,youcoulduseGit'stagfeature,oryoucoulduseGitHub'sreleasefeature.

Tags

Atagisapointerthatpointstoaspecificcommit.Unlikecommits,tagsarenotimmutable.Theycanbemovedandchanged.Let'spracticeabitwithtags.

TagscanbecreatedlocallywithGit,oronGitHub.Whencreatingatagfromthecommandline,it'srecommendedtocreatean"annotated"tag.Thefollowingexamplecreatesanannotatedtagwiththe-aflag,namesthetagv1.0,andconnectsittowhichevercommitSHAisincluded.

gittag-av1.0<SHA>

Toseealltags,typegittag--list.

Anothercaveatwithtagsisthattheyarenotautomaticallypushedupwithcommits.Topushtags,typegitpush--tags.

Youcanalsosetthisasadefaultwithconfigsusinggitconfigpush.followTagstruewhichwillautomaticallypushtagswhentheirassociatedcommitsarepushed.Readmoreaboutthisconfigsetting.

Releases

ReleasesareaGitHubfeaturethatallowyoutoaddanexecutabletothetagforeasieraccessbyvisitorswhojustwanttodownloadandinstallyoursoftware.Releasesaretags,becausetheypointtoaspecificcommitandcanbenamedlikeanyothertag.However,releasescanalsoincludeattachedbinaries.

AddaReleasetoGitHub-Games

1. OnGitHub,navigatetotheCodetaboftherepository.2. Underyourrepositoryname,clickReleases.3. ClickDraftanewrelease.4. Typeanameforthetag.Werecommendyouusesemanticversioning.5. Selectabranchthatcontainstheprojectyouwanttorelease.Usually,you'llwanttoreleaseagainstyourmaster

branch,unlessyou'rereleasingbetasoftware.Youcanalsoselectarecentcommitbychoosingtherecentcommitstab.

6. Typeatitleanddescriptionthatdescribesyourrelease.7. Ifyou'rereadytopublicizeyourrelease,clickPublishrelease.Otherwise,clickSavedrafttoworkonitlater.

Noticethatyoucoulddraganddroporselectfilesmanuallyinthebinariesbox,orselect"Thisisapre-release"tonotifyusersthatit'snotreadyforproduction.

Tags&Releases

46

DiscussionGuide:TeamWorkflowsandBranchingStrategiesNowisagoodtimetodiscussworkflows-whatworksforyouandyourteam,whatmightwork,andwhatyou'vebeendoinginthepast.Herearesometopicsyouwillwanttodiscusswithyourteamasyouestablishyouridealprocess.Haveaconversationeithersynchronouslyorinissuesintheclassrepositoryaboutdifferentworkflows.

1. Whichbranchingstrategywillweuse?2. Whichbranchwillserveasour"master"ordeployedcode?3. Howwillyouprotectyourcode?4. Willweusenamingconventionsforourbranches?5. Howwillweuselabelsandassignees?6. Willweusemilestones?7. WillwehaverequiredelementsofIssuesorPullRequests(e.g.shippingchecklists)?8. Whoisexpectedtoreviewyourwork?Doyouplantoinvolveotherteams?9. Howwillweindicatesign-offonPullRequests?10. Whowillmergepullrequests?11. Howwillyouteachyourworkflowtoyourteam?Ifitalreadyexists,howisittaughttonewhires?12. Whatintegrationswillbeusedindifferentstagesofdevelopment?Willallteamsbeusingthesametools?13. IfusershavequestionsaboutGit,GitHub,ortheirworkflows,whodotheyask?Howdotheyknowwhotoask?

WorkflowDiscussion

47

InitializingaNewLocalRepository

Let'screatealocalrepositorythatwecanusetopracticethenextsetofcommands.

1. Navigatetothedirectorywhereyouwillplaceyourpracticerepo(cd..togetbacktotheparentfolder).2. Createanewdirectoryandinitializeitasagitrepository:gitinitpractice-repo3. CDintoyournewrepository:cdpractice-repo4. CreateanemptynewfilenamedREADME.md:

Bash:touchREADME.mdPowerShell:Out-FileREADME.md

5. AddandcommittheREADME.mdfile.

Sincewewillbeusingthisasourpracticerepository,weneedtogeneratesomefilesandcommits.Herearesomescriptstomakethiseasier:

Bash:

fordin{1..6};dotouch"file${d}.md";gitadd"file${d}.md";gitcommit-m"addingfile${d}";done

PowerShell:

for($d=1;$d-le6;$d++){Out-Filefile$d.md;gitaddfile$d.md;gitcommit-m"addingfile$d.md";}

Youmightseeacommandduringthissection,tree.git.Ifyou'reonamachinewheretree.gitdoesn'twork(probablyaWindowsmachine),trycmd//ctreeinstead.

CreateaLocalRepo

48

FixingCommitMistakesInthisactivity,wewillbegintoexploresomeofthewaysGitandGitHubcanhelpusshapeourprojecthistory.

RevisingYourLastCommit

gitcommit--amendallowsustomakechangestothecommitthatHEADiscurrentlypointingto.Twoofthemostcommonusesare:

Re-writingcommitmessagesAddingfilestothecommit

Let'sseethisinaction:

1. Createanewfile:Bash:touchfile7.mdPowerShell:Out-Filefile7.md

2. Whenyouareaddingfilestothepreviouscommit,theyshouldbeinthestagingarea.Moveyourfiletothestagingarea:gitaddfile7.md

3. gitcommit--amend4. Thetexteditorwillopen,allowingyoutoedityourcommitmessage.

Youcanactuallyamendanydatastoredbythelastcommitsuchascommitauthor,email,etc.

FixingCommitMistakes

49

RewritingHistorywithGitResetWhenyouwanttomakechangestocommitsfurtherbackinhistory,youwillneedtouseamorepowerfulcommand:gitreset.

UnderstandingReset

Sometimesweareworkingonabranchandwedecidethingsaren'tgoingquitelikewehadplanned.Wewanttoresetsome,orevenall,ofourfilestolooklikewhattheywereatadifferentpointinhistory.

Remember,therearethreedifferentsnapshotsofourprojectatanygiventime.Thefirstisthemostrecentcommit(alsoknownasHEAD).Thesecondisthestagingarea(alsocalledtheindex).Thethirdistheworkingdirectorycontaininganynew,deleted,ormodifiedfiles.

Thegitresetcommandhasthreemodes,andtheyallowustochangesomeorallofthesethreesnapshots.

Italsohelpstoknowwhatbranchestechnicallyare:eachisapointer,orreference,tothelatestcommitinalineofwork.Asweaddnewcommits,thecurrentlychecked-outbranch"movesforward,"sothatitalwayspointstothemostrecentcommit.

ResetModes

RewritingHistorywithGitReset

50

Thethreemodesforgitresetare:--soft,--mixed,and--hard.Fortheseexamples,assumethatwehavea"clean"workingdirectory,i.e.therearenouncommitedchanges.

--soft

gitreset--soft<SHA>movesthecurrentbranchtopointatthe<SHA>.However,theworkingdirectoryandstagingarearemainuntouched.Sincethesnapshotthatcurrentbranchpointstonowdiffersfromtheindex'ssnapshot,thiscommandeffectivelystagesalldifferencesbetweenthosesnapshots.Thisisagoodcommandtousewhenyouhavemadealargenumberofsmallcommitsandyouwouldliketoregroupthemintoasinglecommit.

--mixed

gitreset--mixed<SHA>makesthecurrentbranchandthestagingarealooklikethe<SHA>snapshot.Thisisthedefaultmode:ifyoudon'tincludeamodeflag,Gitwillassumeyouwanttodoa--mixedreset.--mixedisusefulifyouwanttokeepallofyourchangesintheworkingdirectory,butchangewhetherandhowyoucommitthosechanges.

--hard

gitreset--hard<SHA>isthemostdrasticoption.Withthis,Gitwillmakeall3snapshots,thecurrentbranch,thestagingarea,andyourworkingdirectory,lookliketheydidat<other-commit>.Thiscanbedangerous!We'veassumedsofarthatourworkingdirectoryisclean.Ifitisnot,andyouhaveuncommittedchanges,gitreset--hardwilldeleteallofthosechanges.Evenwithacleanworkingdirectory,use--hardonlyifyou'resureyouwanttocompletelyundoearlierchanges.

ResetSoft

RewritingHistorywithGitReset

51

Usingthepracticerepositorywecreatedearlier,let'stryareset--soft.

1. Viewthehistoryofourproject:gitlog--oneline--decorate2. IdentifythecurrentlocationofHEAD.3. Gobacktwocommitsinhistory:gitreset--softHEAD~24. Seethetipofourbranch(andHEAD)isnowsittingtwocommitsearlierthanitwasbefore:gitlog--oneline--

decorate

5. Thechangeswemadeinthelasttwocommitsshouldbeinthestagingarea:gitstatus6. Allthefilesstillexistlocally:ls7. Let'sremovetheextrafilewecreatedearlier:gitrm--cachedfile7.md8. Now,we'llre-committhesechangeswithouttheextrafile:gitcommit-m"re-addfile5and6"

Inthisexample,thetildetellsgitwewanttoresettotwocommitsbeforethecurrentlocationofHEAD.YoucanalsousethefirstfewcharactersofthecommitIDtopinpointthelocationwhereyouwouldliketoreset.

ResetMixed

Nextwewilltrythedefaultmodeofreset,reset--mixed:

1. Onceagain,wewillstartbyviewingthehistoryofourproject:gitlog--oneline2. Gobackonecommitinhistory:gitresetHEAD~3. Seewherethetipofthebranchispointing:gitlog--oneline--decorate4. Thechangeswemadeinthelastcommithavebeenmovedbacktotheworkingdirectory:gitstatus5. Allthefilesstillexistlocally:ls6. Movethefilestothestagingareabeforewecancommitthem:gitaddfile5.mdfile6.md7. Re-committhefiles:gitcommit-m"re-addfile5and6"

Noticethatalthoughwehaveessentiallymadetheexactsamecommit(addingfile5and6togetherwiththesameHEADandcommitmessage)westillgetanewcommitID.Thiscanhelpusseewhytheresetcommandshouldneverbeusedoncommitsthathavebeenpushedtotheremote.

ResetHard

Lastbutnotleast,let'stryahardreset.

1. Startbyviewingthehistoryofourprojectwith:gitlog--oneline2. ResettothepointintimewheretheonlyfilethatexistedwastheREADME.md:gitreset--hard<SHA>3. Seethatallofthecommitsaregone:gitlog--oneline4. Noticeyourworkingdirectoryisclean:gitstatus5. SeethattheonlyfilesinyourrepositoryaretheREADME.mdandfile7.md:ls

Warning:Remember,gitreset--hardoverwritesyourworkingdirectory,stagingarea,andhistory.Thismeansthatuncommittedchangesyouhavemadetoyourfileswillbecompletelylost.Don'tuseitunlessyoureallywanttodiscardyourchanges.Anyfilesthatareuntrackedwillremainandbeunchanged.

DoesGoneReallyMeanGone?

Theanswer:Itdepends!

$gitreflog

ThereflogisarecordofeveryplaceHEADhasbeen.Inafewminuteswewillseehowthereflogcanbehelpfulinallowingustorestorepreviouslycommittedchanges.Butfirst,weneedtobeawareofsomeofthereflog'slimitations:

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Thereflogisonlylocal.Itisnotpushedtotheremoteandonlyincludesyourlocalhistory.Inotherwords,youcan'tseethereflogforsomeoneelse'scommitsandtheycan'tseeyours.Thereflogisalimitedtimeoffer.Bydefault,reachablecommitsaredisplayedinthereflogfor90days,butunreachablecommits(meaningcommitsthatarenotattachedtoabranch)areonlydisplayedfor30days.

Sometimes,you'llwanttosaveyourworkinacommitwithouthavingtothinkofacommitmessage,orbeforeyou'rereadytoorganizeyourchanges.Ifthat'sthecase,youcancreatealiasestocreate"savepoints".Seetheappendixwithaliasestolearnhow!

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GettingitBack:gitcherry-pickWejustlearnedhowreflogcanhelpusfindlocalchangesthathavebeendiscarded.Sowhatif:

YouJustWantThatOneCommit

Cherrypickingallowsyoutopickupacommitfromyourreflogoranotherbranchofyourprojectandmoveittoyourcurrentbranch.Rightnow,yourfiledirectoryandlogshouldlooklikethis:

$ls

README.md

$gitlog--oneline

84nqdkqinitializingrepowithREADME

Let'scherrypickthecommitwhereweaddedfile4:

1. FindthecommitIDwhereyouaddedfile4.md:gitreflog2. Cherry-pickthatcommit:gitcherry-pick<SHA>

Nowwhenyouviewyourdirectoryandlog,youshouldsee:

$ls

file4.md

README.md

$gitlog--oneline

eanu482addingfile4

84nqdkqinitializingrepowithREADME

IsthecommitIDthesameastheoneyouusedinthecherrypickcommand?Whyorwhynot?

Remember,whenusinganycommandsthatchangehistory,it'simportanttomakethesechangesbeforepushingtoGitHub.WhenyouchangeacommitIDthathasbeenpushedtotheremote,youriskcreatingproblemsforyourcollaborators.{:.warning}

Oops,IDidn'tMeantoReset

Sometimes,yougitreset--hardalittlefurtherthanintendedandwanttorestorethatwork.Thegoodnewsis,thatgitreset--harddoesn'tjustworkbygoingbackintime,itcanalsogoforward:

1. ViewthehistoryofeverywhereHEADhaspointed:gitreflog2. Resettothepointintimewheretheoriginalfile6.mdwascreated:gitreset--hard<SHA>3. Seeyourrestoredhistory:gitlog--oneline

TakealookatthecommitIDsingitlog--onelinecomparedtogitreflog.Whatdoyounotice?

Whydidn'tthiscommandcauseamergeconflictsincewehadalreadycherry-pickedfile4.Thereasonisthatgitreset--hardisnottryingtomergethetwohistoriestogether,itissimplymovingthebranchtopointtoanewcommit.Inthiscase,thiswaswhatwewanted.Inothercases,thiscouldcauseustoloseanyworkwemayhavedoneaftertheoriginalreset.

Seehowtoavoidtragedywithaconvenientaliasintheappendix.

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MergeStrategies:RebaseInthissection,wewilldiscussanotherpopularmergestrategy,rebasing.

UnderstandingGitMergeStrategies

Gitusesthreeprimarymergestrategies:

FastForward

Afastforwardmergeassumesthatnochangeshavebeenmadeonthebasebranchsincethefeaturebranchwascreated.Thismeansthatthebranchpointerforbasecansimplybe"fastforwarded"topointtothesamecommitasthefeaturebranch.

Recursive

Arecursivemergemeansthatchangeshavebeenmadeonboththebasebranchandthefeaturebranchandgitneedstorecursivelycombinethem.Witharecursivemerge,anew"mergecommit"ismadetomarkthepointintimewhenthetwobranchescametogether.Thismergecommitisspecialbecauseithasmorethanoneparent.

Octopus

Amergeof3ormorebranchesisanoctopusmerge.Thiswillalsocreateamergecommitwithmultipleparents.

AboutGitRebase

gitrebaseenablesyoutomodifyyourcommithistoryinavarietyofways.Forexample,youcanuseittoreordercommits,editthem,squashmultiplecommitsintoone,andmuchmore.

Toenableallofthis,rebasecomesinseveralforms.Fortoday'sclass,we'llbeusinginteractiverebase:gitrebase--interactive,orgitrebase-iforshort.

Typically,youwouldusegitrebase-ito:

ReplayonebranchontopofanotherbranchEditpreviouscommitmessagesCombinemultiplecommitsintooneDeleteorrevertcommitsthatarenolongernecessary

CreatingaLinearHistory

Oneofthemostcommonusesofrebaseistoeliminaterecursivemergesandcreateamorelinearhistory.Inthisactivity,wewilllearnhowitisdone.

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SetUp

1. FindtheSHAoftheinitialcommit:gitlog--oneline2. ResettotheSHAoftheinitialcommit:gitreset--hardSHA3. Createanewbranchandcheckouttoit:gitcheckout-brebase-me4. Cherry-pickfiles4-6ontotherebase-mebranchusingthereflog.5. Checkouttomaster:gitcheckoutmaster6. Cherry-pickfiles1-3ontothemasterbranchusingthereflog.7. Lookatyourhistory:gitlog--oneline--graph--decorate--all8. Ifyoumergednow,itwouldbearecursivemerge.

BegintheRebase

1. Checkouttotherebase-mebranch:gitcheckoutrebase-me2. Startthemerge:gitrebase-imaster3. Yourtexteditorwillopen,allowingyoutoseethecommitstoberebased.4. Saveandclosetherebase-todo.5. Watchyourrebasehappenonthecommandline.6. Takeanotherlookatyourhistory:gitlog--oneline--graph--decorate--all7. Ifyoumergednow,itwouldbeafast-forwardmerge.

FinishtheMerge

1. Checkouttomaster,thebranchyouwillmergeinto:gitcheckoutmaster2. Mergeyourchangesintomaster:gitmergerebase-me

Ifyou'dlikesomehelpkeepingeverythingcleanwithanalias,don'tforgettochecktheappendix!

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