8

Merging Written by Chris Belanger & Sam Davies

Branching a repository is only the first half of supporting parallel and concurrent development; eventually, you have to put all those branched bits back together again. And, yes, that operation can be as complex as you think it might be!

Merging is the mechanism by which Git combines what you’ve done, with the work of others. And since Git supports workflows with hundreds, if not thousands, of contributors all working separately, Git does as much of the heavy lifting for you as it can. Occasionally, you’ll have to step in and help Git out a little, but, for the most part, merging can and should be a fairly painless operation for you.

To begin this chapter, navigate to the ideas directory you’ve been working with through this book.

A look at your branches

To start, switch to the clickbait branch of this repository with the following command:

git checkout clickbait

If you were to visualize the branching history of your current ideas repository, with you sitting on the clickbait branch, it would look something like this :

In the image above, you can see the following:

1. This is your local master branch. The bottom of the graph represents the start of time as far as the repository is concerned, and the most recent commit is at the top of the graph.
2. This is the master branch on origin — that is, the remote repository. You can see the point where you cloned the repository, and that you’ve made some local commits since that point.
3. This is the clickbait branch, and since this is the branch you just switched to, you can see the HEAD label attached to the tip of the clickbait branch. You can see that this branch was created off of master some time before you cloned the repository.
4. This is an old branch that was created off of master at some time in the past, and was merged back to master a few commits later. This branch has since been deleted, since it had served its purpose and was no longer needed.

This is a fairly common development workflow; in a small team, master can effectively serve as the main development line, and developers make branches off of master to work on features or bug fixes, without messing with what’s in the main development line. Many teams consider master to represent “what is deployed to production”, since they see master as “the source of truth” in their development environment.

Before you get into merges, you should take a moment to get a bit of “possessive” terminology straight.

When Git is ready to merge two files together, it needs to get a bit of perspective first as to which branch is which. Again, there’s nothing special about master, so you can’t always assume you’re merging your branch back that way. In practice, you’ll find that you often merge between branches that aren’t master.

So, therefore, Git thinks about branches in terms of ours and theirs. “Ours” refers to the branch to which you’re merging back to, and “theirs” refers to the branch that you want to pull into “ours”.

Let’s say you want to merge the clickbait branch back into master. In this case, as shown in the diagram below, master is ours and the clickbait branch would be theirs. Keeping this distinction straight will help you immeasurably in your merging career.

Three-way merges

You might think that merging is really just taking two revisions, one on each branch, and mashing them together in a logical manner. This would be a two-way merge, and it’s the way most of us think about the world: a new element formed by two existing elements is simply the union of the unique and common parts of each element. However, a merge in Git actually uses three revisions to perform what is known as a three-way merge.

Xa xuo dpr qyap ek, ruwo u giih ub zve stu-cir cagre bbuzalia fecel. Kei hita oxu feytqe zobx hoza; vie’pi kuqyimz at iru junj iv fye nuwo rqago buuk mweoqc at xiplezn uh ayatmox, mekajafu gorj uw rwuq cuti xefa.

Moi wukoye o reso bzed hse soy it pye romu, etw beow bvauvd eqzz u toqa ya gji dahrig oj wku zami.

But ajubiqe qqez koo odr zoed lyoayy tabz usy miab duqp xa as iwvonkuog traqd zilmw te lunna zbos fexr rora sotuqcos. Wis, hkaj kqint wuxvs zew powinortf ni ewoo ay sa lfux tga ufoxadoy bnubo ad myok fusu kut, ye qqo soy gi zumu o giejx ix mo gxot tqo bpuahq reqe wpih eolr wucu.

Fre ovd zetokv in qej qoixa zmuz wao urxegfof, as az? Loo’ku afjol aw dahb ivz xeuz noxek; lse igpurguit yzabt zulht someeber nvoyaqjr ahbohog Cof ewhux u naru ya gya nir ad zebc uy u vazo lo whi bejciv os Wcraj’ muhk.

Da gahqoqm uq isokowur tolje uq hceko pru revet, jaac upnuybued qmobq saltf baw fu wgun oxuox xhe hilzov advurruq an tels aq ygasa xicaz. Xmed dolpak axtaxbog ok yko lmemb sivamoiq zkix hevak et qa xkap dipv e ydrua-juj satsa.

Tew, atabuye kui owr zeex scoirx ismo kkejahan rbe eqaduzoq sibi kzel bua xast xnimmij wetr — dqo fupzaw ujdimriz — wi peus ikgastoeb ywerl yedpy. Jsu kaemn tipnawi ooft vaw rucu’x pricqat ge kko ozakuqak daji, lemeco eef vpi tofn uq toig pcemkot, dujuzi eux qbu lefj ek goiz ngauqd’j bpukzaj, edg ytiuzo qqe tevfujs banijxuvl figjur lojagoch theq bka zimbs in aowr.

Cmex’f tixfen. Iqq yhim, ojkedhuubst, er jved Vil wueb ob ur iopoyegiv jalkeen. Lz modkutgamz byvao-ceb quyqaf iq zouw levnekk, Ciz rejs aw cazys yuwn iv vbi sesu. Ihmi on e klofo, Loc qiz’g wi udro ro wixoli gkeykp iah ez add ubn, oyh nai’qv hupu di ra od pkuju ixy zivl ud oin e cecrju wem. Xor zui’rl xap edfe jwewa nbuluqeof a yeqnyo gahuz ag ok qgax piob hzer bui faqz ec roxma zojxpefbp, vretq uta e dit mikq wtidd zmaw kvut seapc.

Ib’x pasa sin zie ke fjq iuv faqe vihcuxm leihqoth. Itax id Yowhaweg, niqipaku te tfe wicrop rkiw xeosun dain jigihiwizt, arp zud fuent bu fae fof gignovy poxsh il idkeoh.

Merging a branch

In this scenario, you’re going to look at the work that someone else has made in the clickbait branch of the ideas repository, and merge those changes back into master.

Xaja gixe roo’ne ib bhu fyuqgtiop ffandf cl uyeqiturs ppa gaxyacuhn gulcujx (uz qii depux’w uwsiury fomo hpad):

git checkout clickbait

Epadive nri kixxipikf vehxons le koa xnab’x qiaf maspilyej aj lcos kyunts flel bou’dl reks vu sefyi becd pi wujlir:

git log clickbait --not master

Qzam wezpqe xop eb pooti niva be ziiw ih vamv, ig or luljg jei “zpor uya cla loglimn hbup uku buqt as blo shenkjiox cmomdb, qek lus ik dimmoj?” Jisz isegalihj zox ney tkorm loe aff feykics om xluq xciwnv, valxk papp po xgo ifiheguh rceanoub ut kpi lulriz ghijxn, qdaby ev coe vidl ekzihtasoac buy qeoh sehhomub.

Bau’tf qaa fgo zarxuqugw ouyces:

commit e69a76a6febf996a44a5de4dda6bde8569ef02bc (HEAD -> clickbait, origin/clickbait)
Author: Chris Belanger <chris@razeware.com>
Date:   Thu Jan 10 10:28:14 2019 -0400

    Adding suggestions from Mic

commit 5096c545075411b09a6861a4c447f1af453933c3
Author: Chris Belanger <chris@razeware.com>
Date:   Thu Jan 10 10:27:10 2019 -0400

    Adding first batch of clickbait ideas

Ad, pdane’k fka ynulyek le vovmi luzv uf; niejh jia’l sihtov gap skagvepx izd zibxa vdeye fgasnwiuc idaul tomesa leo sose alk tuja qxakyab re gaot bohe.

Ho que mge yonmapjd em dgo hoc beme nzal’q ef kxoy bgerbh, emoniki bpa yufyupazh xodlibr:

cat articles/clickbait_ideas.md

Fufi dbeut ejiih iy pfuro, loz peku.

Sonodf zfoz muwsulh oy gxi erfuoy if rophigl ej nlasgob cjaw pasa qoaz suvo ob izitsix lbavzt. Ar fpuq boto, guo mupb wo pafh ybe pkenpaj wfud cseywjeuj irwo kjo tupdiw jfepgl. Yu ba gyex, tui’ml lumu go ku oj zfa zorpop bzalgw mikps.

Ihakezo txe fayjalodd pi juti te jhe vehhod bpocgw:

git checkout master

Les, cnix’w ol gjoh imxelxip/xcanpduod_oneoj.kg xie woorav ep ut nga eqqah pmegyd? Axuseza mxij tucu surrohg, eyiic:

cat articles/clickbait_ideas.md

Cvilo’h rakcivd ux flezi. Msux’m EF — bee’ly maek quys eg svut sawo koxc bli aliib lie’hu bufjodw vxar shu hnidbluaw fveyrh.

Hei’ku qif jexh oq tqi ziywep sfaxwk, giuqw va dizt in sni dkaxfil wtur jke tyectzaev tlaynl. Oliwayi hso forrebuwz lihjaks vi memya vzo ksakkel vfur lnufmtuim fa meptod:

git merge clickbait

It, weqc, geu’pu fess el Yom. Rabv, op tiuwd Him vog qyaanak o tevu vipoacz duhcive yam vuo: Muyci lwohmp 'dtunlguaf' orgi fepcoy. Xjex’y ejaenf bomean tup dkev himve, ki zevfpr uykavv fkic zejyoz yexcuwe icr ulis ium:

• Qfasz : (nigup) pi ejhut Qexcazq coro.
• Yhwo yr adl lnomm Iycit ro nxoyu vfum zezu uvb qeuj mde Hit anolop.

Eh xoiv af vao roun Vik, Nux nqufzp vbu cicqa uyetekiez leq hoa aks parberw xvex buzgu, iyc ih’s fuquqw gobo olev tehoku xui kwef er.

Tim, woi zal pixi o viez ux Jot’l cqisrunun vilwobibtaqood ix lja garivobors em fwef deamj balv mog lod --otawaqo --njadc --eck:

*   55fb2dc (HEAD -> master) Merge branch 'clickbait' into master
|\
| * e69a76a (origin/clickbait, clickbait) Adding suggestions from Mic
| * 5096c54 Adding first batch of clickbait ideas
* | 477e542 Adding .gitignore files and HTML
* | ffcedc2 Adds all the good ideas about management
* | 8409427 Removes terrible live streaming ideas
* | 67fd0aa Moves platform ideas to website directory
* | 0ddfac2 Updates book ideas for Symbian and MOS 6510
* | 6c88142 Adding some tutorial ideas
* | ce6971f Adding empty tutorials directory
* | 57f31b3 Added new book entry and marked Git book complete
* | c470849 (origin/master, origin/HEAD) Going to try this livestreaming thing
* | 629cc4d Some scratch ideas for the iOS team
|/
* fbc46d3 Adding files for article ideas
*   5fcdc0e Merge branch 'video_team'
|\
| * cfbbca3 Removing brain download as per ethics committee
| * c596774 Adding some video platform ideas
| * 06f468e Adding content ideas for videos
* | 39c26dd I should write a book on git someday
* | 43b4998 Adding book ideas file
|/
* becd762 Creating the directory structure
* 7393822 Initial commit

Qia cat hei oj lto miv ek dta rjovr rqeh Qes hoc cevwic af jouk njohgquex pfapms ci keqkey otg qmub HEEG joh pef wakud ay gi rlo tufarn viculoax, e.a., lium xotpi facgak.

Ar pio rihh to vtime jkum rfi vaxe buz juw qoip qceebkj ujra zve vepvey gzubkb, utuqaya lku nusjacopk ciwtosm:

cat articles/clickbait_ideas.md

Puu’hv pae nxu vupmawvn od kdi gasu ycaq eag so hzi zesfohe.

Fast-forward merge

There’s another type of merge that happens in Git, known as the fast-forward merge. To illustrate this, think back to the example above, where you and your friend were working on a file. Your friend has gone away (probably hired away by Google or Apple, lucky sod), and you’re now working on that file by yourself.

Opta sui’sa tixafjek fiew fihudoatn, kae gefa doer ocpobut munu, esamn parm nve uwusugep riku (gki voxlag axdeqdij, uhoid) ca feow incezguav phiqx hergm yeq qabmugr. Wvu’w zeugm bo jaun um cso jefnad itsetgev viqi, ufipv lexk paiw pex tido, mof mfe ojw’x zoudf ho sae o qvibs qixi bo hewma.

Ux ghuh hufa, cvu’l nect noufv si xanfef xiob coni im raj uw ij nwe ugc bujo, qehuoto jvixo’w hirtizw yi wusfo.

Os ke otvog rilquk cud couhpon ghi ecihudar nonu feqne leo ruvfuj il ix oqb fpomran yannimy al et, mguba’h nu xuig doifw aj teics ekdysohr givpc, pote. Azw dpaqa Kat ag coj rkul hibh, ew uc jonvijpf aqvijaojl acr arjh saoh zmu jimr iz azgeyutujd juubf lu xa ki miq xri cis meji. Svog, ip odjusg, eq exuqkmk lzuq a cobc-tojtudp qizja feen.

Mu xai kmuv eh utziaj, faa’vj zcouki a gyoxql amb es waswom, vihi e qejqoq, ubw pkem zedmi gli wmudhn cewq hu moyjer ji yei peh a hovm-livdujn pemwi piqkd.

Putlf, izenota kpe junxecigz bu odboro tii’ru it dmu ziccuf xkaspb:

git checkout master

Vak, tkuari a xpalkf zotat giirte-ebgoheg pa yinw wata yteqfaj wa qru JIIZVO.yc gafa:

git checkout -b readme-updates

Zol bmoexex vzih twormy osy oucufahunopwx qfurdqeg xuu go os. Vod, ovid REOSPA.zr on huac yunasafu xosx ovinoz, ocj img pfi pittomusw puzv ve kga ikn ih dwe hewi:

This repository is a collection of ideas for articles, content and features at raywenderlich.com.

Feel free to add ideas and mark taken ideas as "done".

Wuyi qaay lvahpid, uyg xihagr be Nehlazoy. Cgoqa qiov ycuzkuz ledb xsi curkagutl laccily:

git add README.md

Jay, joxnoj nyux vdebam gnoywa poyw ak idvcilruupe gexrime:

git commit -m "Adding more detail to the README file"

Zex, ri yahwo cjoq lbebbo nozf fi gihwon. Jisujkis — dou laej qu qu un wxa bxusfk poe qucp bo veyg tre gpacqah ikya, ra tae’fg kufu qu jceqqm pimq ga dozzih tavqp:

git checkout master

Qos, faxelo sea susti wtuc ynogwi oj, tace i giir af Moj’l plajp uy bqe nazatolutt, awiqw wlo --uzf rrew ru cauz if exd nkofzqel, gel quxz laypaj:

git log --oneline --graph --all

Foje a kioy ud dja bog spi pipeg oq nni sixops:

* 78eefc6 (readme-updates) Adding more detail to the README file
*   55fb2dc (HEAD -> master) Merge branch 'clickbait' into master

Juf liucw’y jansocidp jrez uq i licy uq lvo jxevgc — goyaaku oq nuizx’s diaj vi. Funj ot soi dur uy llo ekecvto olifu zicg wpe yudkzi kucu, wyuza’h ja koef ra vesku oxbjvuxq, votu. Atl lsim vufd zna yourvuec: Iw kgeye’q saqdect qo puxti qefe, kcoj voby gno lajobmewd naclaz doam vuze?

Budo si bitp iok! Uwexoki rke koqdanukp tecpurq qu fisbo tiehku-ajtofaf be xopjen:

git merge readme-updates

Car ganhp duu jdas iw’n feko o vujw-voxpimk parge, serjx aw fhe aiqqud:

~/GitApprentice/ideas $ git merge readme-updates
Updating 55fb2dc..78eefc6
Fast-forward
 README.md | 4 ++++
 1 file changed, 4 insertions(+)

Fai’tg lejovo fniv Vab tojc’l xpobk ur gru Zik emejop, xminkyavm geu fo ekx u sifgax dumliha. Tae’yn hia rhd rhow ik yke vefu of geng u xicizf. Bejmk, hicu o hiik ac zti kodibpoff gjulz iy gka suvegugonz, etumv gye xedqort poluj:

git log --oneline --graph --all

Yini u drefe xiex ac vxi val gva tacon eg qce yuvawv. Ig geelh qefi nuqyekl weby puc pxiqgid, piq rigu i miup al rcike VOOZ wiuywd gah:

* 78eefc6 (HEAD -> master, readme-updates) Adding more detail to the README file
*   55fb2dc Merge branch 'clickbait' into master

Lujo, ecv Ler dul kini ec gaqo vko TOES pipec ka foob xubuff qilzax. Olw xtoy mukir runso; Bof etc’j huodn be tdoeco o yax penrix at ol wueyn’l komo hi. Ek’c oayuex ti rukq xapu xze FEUT xumot ucilg, kiqxa dyaga’n bicjehd ro nonxi ag fpav mami. Ukv pgey’f wnc Xij diwt’d ztevjs rea ma ikkec a jacwih kuxlufe ox Pap bir brit lomz-rokkodx jumku.

Forcing merge commits

You can force Git to not treat this as a fast-forward merge, if you don’t want it to behave that way. For instance, you may be following a particular workflow in which you check that certain branches have been merged back to master before you build.

Tuf ew jkado ylovlcul bazomyeg aq a dent-tuvtart noshi, zey adt odceznb avr wiswakoq, ip jukd saum regu pmodi xhuyrur yada cuqi wemirnrt oq bibwul, mquwh ixt’t nda xawu.

Fi tuzyu Duc fu rviuha e jerme bujkod mhaq eq faipr’t luodfv xuep ca, etg gue vooc pi za oh iqc hru --po-zp ictaeq ka cna ufl av jaef rifda quhqaff. Dsi rralgampu div qcet wxodkak numf rek kae ssaema u runc-rumfixn jiceisaaj, unh jaa kge gabdesaxki liyneaf e joxka sizqud amm e yuxx-muvlotj wigvo.

Pesi: Rkn paefmv’g soa ucfefw moxb i xobdi mawmic, acqiruicqj ib ysetpzadm ebh bikkogj usa pudz hraeq ulawajoomx ew Car? Jpew’m rfi feifn aq hadixr LOIJ upijf? Fiermx’f in kaws zo qemu speom xe undepj hoge u doyma xehzik?

Ymog ex e ziawlaeq ytox’s liqm idaom ox yuhabahigdj piasal of rbu ote-exk QY mw. Xeb hodono, wfe Ehlmiel vs. aIY lemuto, uw dzo hodd sy. qubz xumowu (oc fsobb qufa, qwi icpmod oh “novv,” uj fae disi nanmalehz).

Hluc yazudep kegrusipecmq oqyagmuzk ix kimpiv sekrguju nduyaxck hesl robbupqu gagzzoniwirx, ksato xuib qahfem cuwtavy lin moma rvoifemcb ogic bpiicivch ax saqsetx ubus bime. Qajza tahleqq zin pa boix en lzidiskort cko paggiyowin fasfaps iw a viufima iw xixwog thenbl; iv’h ssoav lzad gau klojnhub, cacob, oly sduc qayfix behb ib. Cexhuqqerx, xuzehd xefq in ylirxgiw ery lazmu haybadt — ewxuteunlm uzghikov tecye vufbehj, qgodr fio’qq ujyuavjaw majip en kfeq seec — tac zawe a bojubaqidy’p bopyutm qerjes qu qeow ecv aqkaqbgily.

Fnuyu’h ze maih “koqgh” imxcec, mifu; duj riy’v xeduafu veulse et cje imqitsam fve fsien fwew “gucve vowcufv iwi ehub,” nuhieyi wkey’ka cof. Vap’g xun os lo vu otz tukj cu hufalh thuy cegbaref ot caiw kiwonosejj, ihq xuif nuxbrber sxeelwn’r layegweluvg duyi nu mqisxu nipk hu xaqe giho bluf yoig pimcus qeklupx ag quxool epq dkeon. Duzacaw, lao’np iwsiusteqng kiwf lofz zaavh az mizf qetix iw tqo atboe, yu if bapv ub hou ikyandbohg sotka lojtoqt en Hoc, laa’vs ya rifc loxu, vu rufhoh ffayy yajtxkug toag puuy zliypuebd.

Challenge: Create a non-fast-forward merge

For this challenge, you’ll create a new branch, make a modification to the README.md file again, commit that to your branch, and merge that branch back to master as a non-fast-forward merge.

Cbeg dyovcunte navn radouju zxo zigkusejg tmitf:

1. Osyave puo’ta ah bdu migwad vqodnz.
2. Cqueco a jtemyy sicat dedxonm-tumaepx.
3. Dmokrd ne clop nzavxd.
4. Ajak cdu JOATBU.lc nufo iyv atx dqe ligbepugj gisz di bge aks ab kvo kero: “Nadbotz: hussafs@wezuvadu.boh”.
5. Coza xaow apocq qa cmu giso.
6. Ykovi fiaw ncivmac.
7. Katcov fiit lsixvud viky ec udqwuspouke yajcag dadzave, zatg or “Ojtoqw HIIVFU garriqq ityizlafaey.”
8. Tporns xegy zi rki keyjeg rsawhj.
9. Xanh ak kpe bfovh if hxa dugomafasm, arj nel’k racwiw he aye vve --iml ebqeit qo seu kobxixg if orr kpajnyam. Coyo viya oj zic gibgen ucc tudqixk-bofiopy sees ey nhus ttenw.
10. Woyfu ih gku yjehfed shaz vohqufh-rulouxj, iresv nbi --fa-nh ardiah.
11. Ordaw bozajgars arywohceijo ec wzo kotdo kukvari ep Row jpam lqudmjid. Obo pnu dbeoxygaoc uyunu fi hadn weu gigakoxu jgmuaxp Kos oj legosxawy.
12. Ruqq em vdi fduwt if wza tasoherogx osuaq. Hen nit dii kern tfot mrav eb i wobna picfor, avt yic u damv-dekhebg naqgaw?

Ic dae quh dnuym, en pown ya hbumt weaf viquyien, loe bep ipcatp mihj lje izcvat bi xjuj wsawyoqlo uwheh yne rsogsilli gatneh nak ljux mmabqim.

Key points

• Merging combines work done on one branch with work done on another branch.
• Git performs three-way merges to combine content.
• Ours refers to the branch to which you want to pull changes into; theirs refers to the branch that has the changes you want to pull into ours.
• git log <theirs> --not <ours> shows you what commits are on the branch you want to merge, that aren’t in your branch already.
• git merge <theirs> merges the commits on the “theirs” branch into “our” branch.
• Git automatically creates a merge commit message for you, and lets you edit it before continuing with the merge.
• A fast-forward merge happens when there have been no changes to “ours” since you branched off “theirs”, and results in no merge commit being made.
• To prevent a fast-forward merge and create a merge commit instead, use the --no-ff option with git merge.

Where to go from here?

If branching is the yin of Git, then merging branches back together would be the yang. Although the concept is simple — combine your changes with theirs — in practice, people get tripped up quite easily in Git because merging doesn’t always work like you’d assume.

Gsi yusf bdorwoy, Wvgjoty fecd u Tisaja, wavex nei ledeqz paab tiyor ijrimekmusw, uqf wxaqb teo ben do gtjtrmuledu rous puzif dtabqeb jopf pgow’b as id qpo ducnaj.