table of contents - githubtraining.github.io · getting started with collaboration we will start by...

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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