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CSE 391Lecture 9
VersioncontrolwithGit
slidescreatedbyRuthAnderson,MartyStepp,BrettWortzman andZorah Fungimagesfromhttp://git-scm.com/book/en/http://www.cs.washington.edu/391/
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Problems Working Alone• Everdoneoneofthefollowing?
§ Hadcodethatworked,madeabunchofchangesandsavedit,whichbrokethecode,andnowyoujustwanttheworkingversionback…
§ Accidentallydeletedacriticalfile,hundredsoflinesofcodegone…§ Somehowmessedupthestructure/contentsofyourcodebase,andwanttojust“undo”thecrazyactionyoujustdid
§ Harddrivecrash!!!!Everything’s gone,thedaybeforedeadline.
• Possibleoptions:§ Saveas(MyClass-v1.java)
• Ugh.Justugh.Andnowasinglelinechangeresults induplicatingtheentirefile…
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Problems Working in teams• Whosecomputerstores the"official" copyoftheproject?
§ Canwestoretheprojectfilesinaneutral"official"location?
• Willwebeabletoread/writeeachother'schanges?§ Dowehavetherightfilepermissions?§ Letsjustemailchangedfilesbackandforth!Yay!
• Whathappensifwebothtrytoeditthesamefile?§ Billjustoverwrote afileIworkedonfor6hours!
• Whathappensifwemakeamistakeandcorruptanimportantfile?§ Isthereawaytokeepbackupsofourprojectfiles?
• HowdoIknowwhatcodeeachteammateisworkingon?
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Solution: Version Control• versioncontrolsystem:Softwarethattracksandmanageschangestoasetoffilesandresources.
• Youuseversioncontrolallthetime§ Builtintowordprocessors/spreadsheets/presentation software
• Themagical“undo”buttontakesyoubackto“theversionbeforemylastaction”
§ Wikis• Wikisareallaboutversioncontrol,managingupdates,andallowingrollbackstopreviousversions
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Software Version Control• Manyversioncontrolsystemsaredesignedandusedespeciallyforsoftwareengineeringprojects§ examples:CVS,Subversion(SVN),Git,Monotone,BitKeeper,Perforce
• helpsteamstoworktogetheroncodeprojects§ asharedcopyofallcodefilesthatalluserscanaccess§ keepscurrentversionsofallfiles,andbackupsofpastversions§ canseewhatfilesothershavemodifiedandviewthechanges§ managesconflictswhenmultipleusersmodifythesamefile
§ notparticulartosourcecode;canbeusedforpapers,photos,etc.• butoftenworksbestwithplaintext/codefiles
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Repositories• Repository(aka“repo”):alocationstoringacopyofallfiles.
§ youdon'teditfilesdirectlyintherepo;§ youeditalocalworkingcopyor“workingtree”§ thenyoucommit youreditedfilesintotherepo
• Theremaybeonlyonerepositorythatallusersshare(CVS,Subversion)
• Oreachusercouldalsohavetheirowncopyoftherepository(Git,Mercurial)
• Filesinyourworkingdirectorymustbeaddedtotherepoinordertobetracked.
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What to put in a Repo?• Everythingneeded tocreateyourproject:
§ Sourcecode(Examples: .java,.c,.h,.cpp )§ Buildfiles(Makefile, build.xml)§ Otherresourcesneeded tobuildyourproject:icons,textetc.
• ThingsgenerallyNOTputinarepo(thesecanbeeasilyre-createdandjusttakeupspace):§ Objectfiles(.o)§ Executables(.exe)§ Machine-specificconfigurationfiles
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Repository Location• Cancreatetherepositoryanywhere
§ Canbeonthesamecomputerthatyou’regoingtoworkon,whichmightbeokforapersonalprojectwhereyoujustwantrollbackprotection
• But,usuallyyouwanttherepositorytoberobust:§ Onacomputerthat’supandrunning24/7
• Everyonealwayshasaccesstotheproject§ Onacomputerthathasaredundantfilesystem(ie RAID)
• Nomoreworriesaboutthatharddiskcrashwipingawayyourproject!
• Options:§ attu,CSEGitLab,GitHub(doNOTuseGitHubforhomework!!!)
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Aside: So what is GitHub?• GitHub.com isasiteforonlinestorageof Git repositories.• Manyopensourceprojectsuseit,suchasthe Linuxkernel.• Youcangetfreespaceforopensourceprojectsoryoucanpayforprivateprojects.
• DoNOTuseGitHubtostoreyourhomework!!Question:DoIhavetouseGitHubtouseGit?Answer:No!• youcanuseGit completely locallyforyourownpurposes,or• youcanusetheCSEGitLab server,or• youcouldsharearepowithusersonthesamefilesystem(e.g.attu)aslongeveryone hastheneeded filepermissions.
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Git
HTTP://XKCD.COM/1597/
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Git Resources• Atthecommandline:(where<verb> = config,add,commit,etc.)
$ git help <verb> $ git <verb> --help $ man git-<verb>
• Freeon-linebook: https://git-scm.com/book/en/v2• Git tutorial:http://schacon.github.com/git/gittutorial.html• ReferencepageforGit:http://gitref.org/index.html• Git website:http://git-scm.com/
• Git forComputerScientists:http://eagain.net/articles/git-for-computer-scientists/
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History of Git• CameoutofLinuxdevelopment community• LinusTorvalds,2005• Initialgoals:
§ Speed§ Supportfornon-lineardevelopment (thousandsofparallelbranches)§ Fullydistributed§ AbletohandlelargeprojectslikeLinuxefficiently
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Git uses a distributed model
Centralized Model Distributed Model
(CVS, Subversion, Perforce) (Git, Mercurial)Result: Many operations are local
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Ways to use Git
Using Git on your own computer, one user
Using Git on multiple computers,multiple users or one user onmultiple computers
Possible servers:• CSE GitLab• attu• GitHub (NOT for homework!)
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Git Operations
Working changes
Changes you’re
prepping to commit
Local copy of the repo with your commitedchanges
Remoteshared
repo
also called “stage”
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Git Operations
git add
git commit
git push
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Basic WorkflowBasicGit workflow:
1. Modify filesinyourworkingdirectory.2. Stage files,addingsnapshotsofthemtoyourstagingarea.3. Doacommit,whichtakesthefilesastheyareinthestagingarea
andstoresthatsnapshotpermanentlytoyourlocalGit directory(yourlocalcopyoftherepo).
• Notes:§ Ifaparticularversionofafileisinyourlocalgit directory,it’sconsideredcommitted.§ Ifit’smodifiedbuthasbeenaddedtothestagingarea,itisstaged.§ Ifitwaschanged since itwascheckedoutbuthasnot beenstaged,itismodified.
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CSE GitLabEveryone inthiscoursehasbeengivenanaccountonCSEGitLabTouseCSEGitLab:1. LogontoCSEGitLab:https://gitlab.cs.washington.edu/
§ IMPORTANT:IfyouhaveaCSENetID usethat,otherwiseuseyourUWNetID
2. Addanssh key:https://gitlab.cs.washington.edu/help/ssh/README.md
§ FollowtheinstructionsinREADME.mdwhichsaytotype:ssh-keygen -t rsa -C "[email protected]" -b 4096
• Justhitreturntoacceptthedefaultfilelocationandyoudonotneedapassword so hitreturnbothtimes when prompted forapassword
§ Thentype: cat ~/.ssh/id_rsa.pub
§ Copy-pastethekeytothe'SSHKeys'sectionunder‘ProfileSettings'inyouruserprofileonCSEGitLab.Orgodirectlyhere:https://gitlab.cs.washington.edu/profile/keys
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Get ready to use Git!1. SetthenameandemailforGit tousewhenyoucommit:
$ git config --global user.name “Bugs Bunny”$ git config --global user.email [email protected]
§ Youcancallgit config –-list toverifytheseareset.§ ThesewillbesetgloballyforallGit projectsyouworkwith.§ Youcansetvariablesonaproject-onlybasisbynot usingthe--global flag.
• Thelatestversionofgit willalsopromptyouthatpush.default isnotset,youcanmakethiswarninggoawaywith:$ git config --global push.default simple
• Youcanalsosettheeditorusedforwritingcommitmessages:$git config --global core.editor emacs (itisvimbydefault)
vim tips: “a” add, “esc” when done adding, “wq:” to save and quitvim editor: http://www.gentoo.org/doc/en/vi-guide.xmlvim ref card: http://tnerual.eriogerg.free.fr/vimqrc.pdf
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Create a local copy of a repo2. Twocommonscenarios:(onlydooneofthese)
a) Tocloneanalreadyexistingrepotoyourcurrentdirectory:$ git clone <url> [local dir name]Thiswillcreateadirectorynamed localdir name,containingaworkingcopyofthefilesfromtherepo,anda.git directorywhichyoucanignore(usedtoholdthestagingareaandyourlocalrepo)
Example:git clone [email protected]:rea/superTest.git
b) TocreateaGit repoinyourcurrentdirectory:$ git initThiswillcreatea.git directoryinyourcurrentdirectorywhichyoucanignore(usedtoholdthestagingareaandyourlocalrepo).Thenyoucancommitfilesinyourcurrentdirectoryintothelocalrepo:$ git add file1.java$ git commit –m “initial project version”
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Git commandscommand description
git clone url [dir] copyagitrepositorysoyoucanaddtoitgit add files addsfilecontentstothestagingareagit commit recordsasnapshotofthestagingareagit status viewthestatusofyourfilesintheworking
directoryandstagingareagit diff showsdiffofwhatisstagedandwhatis
modifiedbutunstagedgit help [command] gethelpinfoaboutaparticularcommandgit pull fetchfromaremoterepoandtrytomerge
intothecurrentbranchgit push pushyournewbranchesanddatatoa
remoterepositoryothers: init, reset, branch, checkout, merge, log, tag
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Adding & Committing files1. Thefirsttimeweaskafiletobetracked,and everytimebefore
wecommitafilewemustaddittothestagingarea:$ git add README.txt hello.java
Thistakesasnapshotofthesefilesatthispointintimeandaddsittothestagingarea.Note:Tounstage achangeonafilebeforeyouhavecommittedit:$ git reset HEAD filename
2. Tomovestagedchangesintothelocalrepowecommit:$ git commit –m “Fixing bug #22”Note:Youcanedityourmostrecentcommitmessage (ifyouhavenotpushedyourcommityet)using:git commit –-amend
Note:Thesecommandsarejustactingonyourlocalversionofrepo.
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Use Good Commit Messages
HTTP://XKCD.COM/1296/
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Status and Diff• Toviewthestatus ofyourfilesintheworkingdirectoryandstagingarea:
$ git status or$ git status –s
(-s showsashortonelineversion)
• Toseedifference between yourworkingdirectoryandthestagingarea(Thisshowswhatismodifiedbutunstaged):
$ git diff
• Toseedifferencebetweenthestagingareaandyourlocalcopyoftherepo(Thisshowsstagedchanges):(--staged is synonymous)
$ git diff --cached
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After editing a file…$emacs rea.txt$git status#Onbranchmaster#Changesnotstagedforcommit:#(use"git add<file>..."toupdatewhatwillbecommitted)#(use"git checkout-- <file>..."todiscardchangesinworkingdirectory)##modified:rea.txt#nochangesaddedtocommit(use"git add"and/or"git commit-a")$git status-sMrea.txt ß Note:Misinsecondcolumn=“workingtree”$git diff ß Showsmodificationsthathavenot beenstaged.diff--git a/rea.txtb/rea.txtindex66b293d..90b65fd100644--- a/rea.txt+++b/rea.txt@@-1,2+1,4@@Here isrea's file.++Onenewlineadded.$git diff--cached ß Showsnothing,nomodificationshavebeenstagedyet.$
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After adding file to staging area…$git addrea.txt$git status#Onbranchmaster#Changestobecommitted:#(use"git resetHEAD<file>..."tounstage)##modified:rea.txt#$git status-sMrea.txt ß Note:Misinfirstcolumn=“stagingarea”$git diff ß Note:Showsnothing,nomodificationsthathavenot beenstaged.$git diff--cached ß Note:Showsstagedmodifications.diff--git a/rea.txtb/rea.txtindex66b293d..90b65fd100644--- a/rea.txt+++b/rea.txt@@-1,2+1,4@@Here isrea's file.++Onenewlineadded.
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Viewing logsToseealogofallchangesinyourlocalrepo:• $ git log or• $ git log --oneline (toshowashorterversion)
1677b2dEditedfirstlineofreadme258efa7Addedlinetoreadme0e52da7Initialcommit
• git log -5 (toshowonlythe5mostrecentupdates,etc.)
Note:changeswillbelistedbycommitID #,(SHA-1hash)Note:changesmadetotheremoterepobeforethelasttimeyoucloned/pulledfromitwillalsobeincludedhere
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Pulling and PushingGoodpractice:1. AddandCommit yourchangestoyourlocalrepo2. Pull fromremoterepo togetmostrecentchanges(fixconflictsif
necessary, thenaddandcommitthosechangestoyourlocalrepo)3. Push yourchangestotheremoterepo
Tofetchthemostrecentupdatesfromtheremoterepointoyourlocalrepo,andputthemintoyourworkingdirectory:$ git pull origin masterTopushyourchangesfromyourlocalrepototheremoterepo:$ git push origin masterNotes: origin =analiasfortheURLyouclonedfrom
master =theremotebranchyouarepullingfrom/pushingto,(thelocalbranchyouarepullingto/pushingfromisyourcurrentbranch)
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Avoiding Common ProblemsFromCSE331:http://courses.cs.washington.edu/courses/cse331/18wi/tools/versioncontrol.html#git-pitfalls
• Donotedittherepository(the .git directory)manually.Itwasn'tdesignedformodificationsbyhumans.
• Trynottomakemanydrasticchangesatonce.Instead,makemultiplecommits,eachofwhichhasasinglelogicalpurpose.Thiswillminimizemergeconflicts.Thisisgoodcodingpracticeingeneral.
• Always git pull beforeeditingafile.It'seasytoforgetthis.Ifyouforget,youmayendupeditinganoutdated version,whichcancausenastymergeconflicts.
• Don'tforget git push afteryouhavemadeandcommittedchanges.Theyarenotcopiedtotheremoterepositoryuntilyoudoapush.
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BranchingTocreateabranchcalledexperimental:• $ git branch experimental
Tolistallbranches:(*showswhichoneyouarecurrentlyon)• $ git branch
Toswitchtotheexperimentalbranch:• $ git checkout experimental
Lateron,changesbetween thetwobranchesdiffer,tomergechangesfromexperimental intothemaster:• $ git checkout master• $ git merge experimental
Note:git log --graph canbeusefulforshowingbranches.Note:Thesebranchesareinyourlocalrepo!
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SVN vs. Git• SVN:
§ centralrepositoryapproach– themainrepository istheonly“true”source,onlythemainrepositoryhasthecompletefilehistory
§ Userscheckoutlocalcopiesofthecurrentversion• Git:
§ Distributedrepositoryapproach– every checkoutoftherepository isafullfledgedrepository,completewithhistory
§ Greaterredundancyandspeed§ Branchingandmergingrepositories ismoreheavilyusedasaresult
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Wrap-up• You*will*useversioncontrolsoftwarewhenworkingonprojects,bothhereandinindustry§ Ratherfoolishnotto§ Advice:justsetuparepository,evenforsmallprojects,itwillsaveyoutimeandhassle
• HW9(Git)hasmoredetailsandwalksyouthroughcreatingaGitrepoandaddingtoasharedrepo.
