EffectiveawkProgramming
ArnoldRobbins


Tomyparents,fortheirlove,andforthewonderfulexampletheysetforme.
TomywifeMiriam,formakingmecomplete.Thankyouforbuildingyourlifetogether
withme.
ToourchildrenChana,Rivka,Nachum,andMalka,forenricheningourlivesin
innumerableways.



ForewordtotheThirdEdition
MichaelBrennan
Authorofmawk
ArnoldRobbinsandIaregoodfriends.Wewereintroducedin1990bycircumstances—
andourfavoriteprogramminglanguage,awk.Thecircumstancesstartedacoupleofyears
earlier.IwasworkingatanewjobandnoticedanunpluggedUnixcomputersittinginthe
corner.Nooneknewhowtouseit,andneitherdidI.However,acoupleofdayslater,it
wasrunning,andIwasrootandtheone-and-onlyuser.Thatday,Ibeganthetransition
fromstatisticiantoUnixprogrammer.
OnoneofmanytripstothelibraryorbookstoreinsearchofbooksonUnix,Ifoundthe
grayawkbook,a.k.a.AlfredV.Aho,BrianW.Kernighan,andPeterJ.Weinberger’sThe
AWKProgrammingLanguage(Addison-Wesley,1988).awk’ssimpleprogramming
paradigm—findapatternintheinputandthenperformanaction—oftenreduced
complexortediousdatamanipulationstoafewlinesofcode.Iwasexcitedtotrymyhand
atprogramminginawk.
Alas,theawkonmycomputerwasalimitedversionofthelanguagedescribedinthegray
book.Idiscoveredthatmycomputerhad“oldawk”andthebookdescribed“newawk.”I

learnedthatthiswastypical;theoldversionrefusedtostepasideorrelinquishitsname.If
asystemhadanewawk,itwasinvariablycallednawk,andfewsystemshadit.Thebest
waytogetanewawkwastoftpthesourcecodeforgawkfromprep.ai.mit.edu.gawk
wasaversionofnewawkwrittenbyDavidTruemanandArnold,andavailableunderthe
GNUGeneralPublicLicense.
(Incidentally,it’snolongerdifficulttofindanewawk.gawkshipswithGNU/Linux,and
youcandownloadbinariesorsourcecodeforalmostanysystem;mywifeusesgawkon
herVMSbox.)
MyUnixsystemstartedoutunpluggedfromthewall;itcertainlywasnotpluggedintoa
network.So,oblivioustotheexistenceofgawkandtheUnixcommunityingeneral,and
desiringanewawk,Iwrotemyown,calledmawk.BeforeIwasfinished,Iknewabout
gawk,butitwastoolatetostop,soIeventuallypostedtoacomp.sourcesnewsgroup.
Afewdaysaftermyposting,IgotafriendlyemailfromArnoldintroducinghimself.He
suggestedwesharedesignandalgorithmsandattachedadraftofthePOSIXstandardso
thatIcouldupdatemawktosupportlanguageextensionsaddedafterpublicationofThe
AWKProgrammingLanguage.
Frankly,ifourroleshadbeenreversed,Iwouldnothavebeensoopenandweprobably
wouldhavenevermet.I’mgladwedidmeet.Heisanawkexpert’sawkexpertanda
genuinelyniceperson.Arnoldcontributessignificantamountsofhisexpertiseandtimeto
theFreeSoftwareFoundation.
Thisbookisthegawkreferencemanual,butatitscoreitisabookaboutawkprogramming
thatwillappealtoawideaudience.Itisadefinitivereferencetotheawklanguageas
definedbythe1987BellLaboratoriesreleaseandcodifiedinthe1992POSIXUtilities


standard.
Ontheotherhand,thenoviceawkprogrammercanstudyawealthofpracticalprograms
thatemphasizethepowerofawk’sbasicidioms:data-drivencontrolflow,patternmatching
withregularexpressions,andassociativearrays.Thoselookingforsomethingnewcantry
outgawk’sinterfacetonetworkprotocolsviaspecial/inetfiles.

Theprogramsinthisbookmakeclearthatanawkprogramistypicallymuchsmallerand
fastertodevelopthanacounterpartwritteninC.Consequently,thereisoftenapayoffto
prototypinganalgorithmordesigninawktogetitrunningquicklyandexposeproblems
early.Often,theinterpretedperformanceisadequateandtheawkprototypebecomesthe
product.
Thenewpgawk(profilinggawk)producesprogramexecutioncounts.Irecently
experimentedwithanalgorithmthatfornlinesofinputexhibited∼Cn2performance,
whiletheorypredicted∼Cnlognbehavior.Afewminutesporingovertheawkprof.out
profilepinpointedtheproblemtoasinglelineofcode.pgawkisawelcomeadditiontomy
programmer’stoolbox.
Arnoldhasdistilledoveradecadeofexperiencewritingandusingawkprograms,and
developinggawk,intothisbook.Ifyouuseawkorwanttolearnhow,thenreadthisbook.



ForewordtotheFourthEdition
MichaelBrennan
Authorofmawk
Somethingsdon’tchange.ThirteenyearsagoIwrote:“Ifyouuseawkorwanttolearn
how,thenreadthisbook.”Truethen,andstilltruetoday.
Learningtouseaprogramminglanguageisaboutmorethanmasteringthesyntax.One
needstoacquireanunderstandingofhowtousethefeaturesofthelanguagetosolve
practicalprogrammingproblems.Afocusofthisbookismanyexamplesthatshowhowto
useawk.
Somethingsdochange.Ourcomputersaremuchfasterandhavemorememory.
Consequently,speedandstorageinefficienciesofahigh-levellanguagematterless.
PrototypinginawkandthenrewritinginCforperformancereasonshappensless,because
moreoftentheprototypeisfastenough.
Ofcourse,therearecomputingoperationsthatarebestdoneinCorC++.Withgawk4.1
andlater,youdonothavetochoosebetweenwritingyourprograminawkorinC/C++.

YoucanwritemostofyourprograminawkandtheaspectsthatrequireC/C++capabilities
canbewritteninC/C++,andthenthepiecesgluedtogetherwhenthegawkmoduleloads
theC/C++moduleasadynamicplug-in.Chapter16hasallthedetails,and,asexpected,
manyexamplestohelpyoulearntheinsandouts.
Ienjoyprogramminginawkandhadfun(re)readingthisbook.Ithinkyouwill,too.



Preface
ArnoldRobbins
NofAyalon
Israel
Severalkindsoftasksoccurrepeatedlywhenworkingwithtextfiles.Youmightwantto
extractcertainlinesanddiscardtherest.Oryoumayneedtomakechangeswherever
certainpatternsappear,butleavetherestofthefilealone.Suchjobsareofteneasywith
awk.Theawkutilityinterpretsaspecial-purposeprogramminglanguagethatmakesiteasy
tohandlesimpledata-reformattingjobs.
TheGNUimplementationofawkiscalledgawk;ifyouinvokeitwiththeproperoptionsor
environmentvariables,itisfullycompatiblewiththePOSIX[1]specificationoftheawk
languageandwiththeUnixversionofawkmaintainedbyBrianKernighan.Thismeans
thatallproperlywrittenawkprogramsshouldworkwithgawk.Somostofthetime,we
don’tdistinguishbetweengawkandotherawkimplementations.
Usingawkyoucan:
Managesmall,personaldatabases
Generatereports
Validatedata
Produceindexesandperformotherdocument-preparationtasks
Experimentwithalgorithmsthatyoucanadaptlatertoothercomputerlanguages
Inaddition,gawkprovidesfacilitiesthatmakeiteasyto:
Extractbitsandpiecesofdataforprocessing

Sortdata
Performsimplenetworkcommunications
Profileanddebugawkprograms
ExtendthelanguagewithfunctionswritteninCorC++
Thisbookteachesyouabouttheawklanguageandhowyoucanuseiteffectively.You
shouldalreadybefamiliarwithbasicsystemcommands,suchascatandls,[2]aswellas
basicshellfacilities,suchasinput/output(I/O)redirectionandpipes.
Implementationsoftheawklanguageareavailableformanydifferentcomputing
environments.Thisbook,whiledescribingtheawklanguageingeneral,alsodescribesthe
particularimplementationofawkcalledgawk(whichstandsfor“GNUawk”).gawkrunson
abroadrangeofUnixsystems,rangingfromIntel-architecturePC-basedcomputersup
throughlarge-scalesystems.gawkhasalsobeenportedtoMacOSX,MicrosoftWindows
(allversions),andOpenVMS.[3]


Historyofawkandgawk
RECIPEFORAPROGRAMMINGLANGUAGE
1partegrep 1partsnobol
2partsed

3partsC

Blendallpartswellusinglexandyacc.Documentminimallyandrelease.
Aftereightyears,addanotherpartegrepandtwomorepartsC.Documentverywellandrelease.

Thenameawkcomesfromtheinitialsofitsdesigners:AlfredV.Aho,PeterJ.Weinberger,
andBrianW.Kernighan.Theoriginalversionofawkwaswrittenin1977atAT&TBell
Laboratories.In1985,anewversionmadetheprogramminglanguagemorepowerful,
introducinguser-definedfunctions,multipleinputstreams,andcomputedregular
expressions.ThisnewversionbecamewidelyavailablewithUnixSystemVRelease3.1

(1987).TheversioninSystemVRelease4(1989)addedsomenewfeaturesandcleaned
upthebehaviorinsomeofthe“darkcorners”ofthelanguage.Thespecificationforawkin
thePOSIXCommandLanguageandUtilitiesstandardfurtherclarifiedthelanguage.Both
thegawkdesignersandtheoriginalawkdesignersatBellLaboratoriesprovidedfeedback
forthePOSIXspecification.
PaulRubinwrotegawkin1986.JayFenlasoncompletedit,withadvicefromRichard
Stallman.JohnWoodscontributedpartsofthecodeaswell.In1988and1989,David
Trueman,withhelpfromme,thoroughlyreworkedgawkforcompatibilitywiththenewer
awk.Circa1994,Ibecametheprimarymaintainer.Currentdevelopmentfocusesonbug
fixes,performanceimprovements,standardscompliance,and,occasionally,newfeatures.
InMay1997,JürgenKahrsfelttheneedfornetworkaccessfromawk,andwithalittle
helpfromme,setaboutaddingfeaturestodothisforgawk.Atthattime,healsowrotethe
bulkofTCP/IPInternetworkingwithgawk(aseparatedocument,availableaspartofthe
gawkdistribution).Hiscodefinallybecamepartofthemaingawkdistributionwithgawk
version3.1.
JohnHaquerewrotethegawkinternals,intheprocessprovidinganawk-leveldebugger.
Thisversionbecameavailableasgawkversion4.0in2011.
SeeMajorContributorstogawkforafulllistofthosewhohavemadeimportant
contributionstogawk.


ARosebyAnyOtherName
Theawklanguagehasevolvedovertheyears.FulldetailsareprovidedinAppendixA.
Thelanguagedescribedinthisbookisoftenreferredtoas“newawk.”Byanalogy,the
originalversionofawkisreferredtoas“oldawk.”
Onmostcurrentsystems,whenyouruntheawkutilityyougetsomeversionofnewawk.[4]
Ifyoursystem’sstandardawkistheoldone,youwillseesomethinglikethisifyoutrythe
testprogram:
$awk1/dev/null
error→awk:syntaxerrornearline1

error→awk:bailingoutnearline1

Inthiscase,youshouldfindaversionofnewawk,orjustinstallgawk!
Throughoutthisbook,wheneverwerefertoalanguagefeaturethatshouldbeavailablein
anycompleteimplementationofPOSIXawk,wesimplyusethetermawk.Whenreferring
toafeaturethatisspecifictotheGNUimplementation,weusethetermgawk.


UsingThisBook
Thetermawkreferstoaparticularprogramaswellastothelanguageyouusetotellthis
programwhattodo.Whenweneedtobecareful,wecallthelanguage“theawk
language,”andtheprogram“theawkutility.”Thisbookexplainsbothhowtowrite
programsintheawklanguageandhowtoruntheawkutility.Theterm“awkprogram”
referstoaprogramwrittenbyyouintheawkprogramminglanguage.
Primarily,thisbookexplainsthefeaturesofawkasdefinedinthePOSIXstandard.Itdoes
sointhecontextofthegawkimplementation.Whiledoingso,italsoattemptstodescribe
importantdifferencesbetweengawkandotherawkimplementations.Finally,itnotesany
gawkfeaturesthatarenotinthePOSIXstandardforawk.
Thisbookhasthedifficulttaskofbeingbothatutorialandareference.Ifyouarea
novice,feelfreetoskipoverdetailsthatseemtoocomplex.Youshouldalsoignorethe
manycross-references;theyarefortheexpertuserandfortheonlineInfoandHTML
versionsofthebook.
Therearesidebarsscatteredthroughoutthebook.Theyaddamorecompleteexplanation
ofpointsthatarerelevant,butnotlikelytobeofinterestonfirstreading.
Mostofthetime,theexamplesusecompleteawkprograms.Someofthemoreadvanced
sectionsshowonlythepartoftheawkprogramthatillustratestheconceptbeingdescribed.
Althoughthisbookisaimedprincipallyatpeoplewhohavenotbeenexposedtoawk,there
isalotofinformationherethateventheawkexpertshouldfinduseful.Inparticular,the
descriptionofPOSIXawkandtheexampleprogramsinChapter10andChapter11should
beofinterest.

Thisbookissplitintoseveralparts,asfollows:
PartI,describestheawklanguageandthegawkprogramindetail.Itstartswiththe
basics,andcontinuesthroughallofthefeaturesofawk.Itcontainsthefollowing
chapters:
Chapter1,GettingStartedwithawk,providestheessentialsyouneedtoknowtobegin
usingawk.
Chapter2,Runningawkandgawk,describeshowtorungawk,themeaningofits
command-lineoptions,andhowitfindsawkprogramsourcefiles.
Chapter3,RegularExpressions,introducesregularexpressionsingeneral,andin
particulartheflavorssupportedbyPOSIXawkandgawk.
Chapter4,ReadingInputFiles,describeshowawkreadsyourdata.Itintroducesthe
conceptsofrecordsandfields,aswellasthegetlinecommand.I/Oredirectionisfirst
describedhere.NetworkI/Oisalsobrieflyintroducedhere.
Chapter5,PrintingOutput,describeshowawkprogramscanproduceoutputwith
printandprintf.
Chapter6,Expressions,describesexpressions,whicharethebasicbuildingblocksfor
gettingmostthingsdoneinaprogram.
Chapter7,Patterns,Actions,andVariables,describeshowtowritepatternsfor
matchingrecords,actionsfordoingsomethingwhenarecordismatched,andthe
predefinedvariablesawkandgawkuse.


Chapter8,Arraysinawk,coversawk’soneandonlydatastructure:theassociative
array.Deletingarrayelementsandwholearraysisdescribed,aswellassortingarrays
ingawk.Thechapteralsodescribeshowgawkprovidesarraysofarrays.
Chapter9,Functions,describesthebuilt-infunctionsawkandgawkprovide,aswellas
howtodefineyourownfunctions.Italsodiscusseshowgawkletsyoucallfunctions
indirectly.
PartII,showshowtouseawkandgawkforproblemsolving.Thereislotsofcodehere
foryoutoreadandlearnfrom.Thispartcontainsthefollowingchapters:

Chapter10,ALibraryofawkFunctions,providesanumberoffunctionsmeanttobe
usedfrommainawkprograms.
Chapter11,PracticalawkPrograms,providesmanysampleawkprograms.
Readingthesetwochaptersallowsyoutoseeawksolvingrealproblems.
PartIII,focusesonfeaturesspecifictogawk.Itcontainsthefollowingchapters:
Chapter12,AdvancedFeaturesofgawk,describesanumberofadvancedfeatures.Of
particularnotearetheabilitiestocontroltheorderofarraytraversal,havetwo-way
communicationswithanotherprocess,performTCP/IPnetworking,andprofileyour
awkprograms.
Chapter13,Internationalizationwithgawk,describesspecialfeaturesfortranslating
programmessagesintodifferentlanguagesatruntime.
Chapter14,DebuggingawkPrograms,describesthegawkdebugger.
Chapter15,ArithmeticandArbitrary-PrecisionArithmeticwithgawk,describes
advancedarithmeticfacilities.
Chapter16,WritingExtensionsforgawk,describeshowtoaddnewvariablesand
functionstogawkbywritingextensionsinCorC++.
PartIV,providesthefollowingappendices,includingtheGNUGeneralPublic
License:
AppendixA,describeshowtheawklanguagehasevolvedsinceitsfirstreleasetothe
present.Italsodescribeshowgawkhasacquiredfeaturesovertime.
AppendixB,describeshowtogetgawk,howtocompileitonPOSIX-compatible
systems,andhowtocompileanduseitondifferentnon-POSIXsystems.Italso
describeshowtoreportbugsingawkandwheretogetotherfreelyavailableawk
implementations.
AppendixC,presentsthelicensethatcoversthegawksourcecode.
Theversionofthisbookdistributedwithgawkcontainsadditionalappendicesandother
endmaterial.Tosavespace,wehaveomittedthemfromtheprintededition.Youmayfind
themonline,asfollows:
Theappendixonimplementationnotesdescribeshowtodisablegawk’sextensions,
howtocontributenewcodetogawk,wheretofindinformationonsomepossiblefuture

directionsforgawkdevelopment,andthedesigndecisionsbehindtheextensionAPI.
Theappendixonbasicconceptsprovidessomeverycursorybackgroundmaterialfor
thosewhoarecompletelyunfamiliarwithcomputerprogramming.


Theglossarydefinesmost,ifnotall,ofthesignificanttermsusedthroughoutthebook.
Ifyoufindtermsthatyouaren’tfamiliarwith,trylookingthemuphere.
TheGNUFDListhelicensethatcoversthisbook.
Someofthechaptershaveexercisesections;thesehavealsobeenomittedfromtheprint
editionbutareavailableonline.


TypographicalConventions
ThisbookiswritteninTexinfo,theGNUdocumentationformattinglanguage.Asingle
Texinfosourcefileisusedtoproduceboththeprintedandonlineversionsofthe
documentation.Becauseofthis,thetypographicalconventionsareslightlydifferentthan
inotherbooksyoumayhaveread.
Examplesyouwouldtypeatthecommandlineareprecededbythecommonshellprimary
andsecondaryprompts,‘$’and‘>’.Inputthatyoutypeisshownlikethis.Outputfrom
thecommand,usuallyitsstandardoutput,appearslikethis.Errormessagesandother
outputonthecommand’sstandarderrorareprecededbytheglyph“error→”.For
example:
$echohionstdout
hionstdout
$echohelloonstderr1>&2
error→helloonstderr

Inthetext,almostanythingrelatedtoprogramming,suchascommandnames,variable
andfunctionnames,andstring,numericandregexpconstantsappearinthisfont.Code
fragmentsappearinthesamefontandquoted,‘likethis’.Thingsthatarereplacedby

theuserorprogrammerappearinthisfont.Optionslooklikethis:-f.Filenamesare
indicatedlikethis:/path/to/ourfile.Thefirstoccurrenceofanewtermisusuallyits
definitionandappearsinthesamefontasthepreviousoccurrenceof“definition”inthis
sentence.
Charactersthatyoutypeatthekeyboardlooklikethis.Inparticular,therearespecial
characterscalled“controlcharacters.”Thesearecharactersthatyoutypebyholdingdown
boththeCONTROLkeyandanotherkey,atthesametime.Forexample,aCtrl-distyped
byfirstpressingandholdingtheCONTROLkey,nextpressingthedkey,andfinally
releasingbothkeys.
Forthesakeofbrevity,throughoutthisbook,werefertoBrianKernighan’sversionofawk
as“BWKawk.”(SeeOtherFreelyAvailableawkImplementationsforinformationonhis
andotherversions.)
NOTE
Notesofinterestlooklikethis.
CAUTION
Cautionaryorwarningnoteslooklikethis.

DarkCorners
Darkcornersarebasicallyfractal—nomatterhowmuchyouilluminate,there’salwaysasmallerbutdarkerone.
—BrianKernighan

UntilthePOSIXstandard(andEffectiveawkProgramming),manyfeaturesofawkwere
eitherpoorlydocumentedornotdocumentedatall.Descriptionsofsuchfeatures(often
called“darkcorners”)arenotedinthisbookwith“(d.c.).”
But,asnotedbytheopeningquote,anycoverageofdarkcornersisbydefinition
incomplete.


Extensionstothestandardawklanguagethataresupportedbymorethanoneawk
implementationaremarked“(c.e.)”for“commonextension.”



TheGNUProjectandThisBook
TheFreeSoftwareFoundation(FSF)isanonprofitorganizationdedicatedtothe
productionanddistributionoffreelydistributablesoftware.ItwasfoundedbyRichardM.
Stallman,theauthoroftheoriginalEmacseditor.GNUEmacsisthemostwidelyused
versionofEmacstoday.
TheGNU[5]ProjectisanongoingeffortonthepartoftheFreeSoftwareFoundationto
createacomplete,freelydistributable,POSIX-compliantcomputingenvironment.The
FSFusestheGNUGeneralPublicLicense(GPL)toensurethatitssoftware’ssourcecode
isalwaysavailabletotheenduser.TheGPLappliestotheClanguagesourcecodefor
gawk.TofindoutmoreabouttheFSFandtheGNUProjectonline,seetheGNUProject’s
homepage.ThisbookmayalsobereadfromGNU’swebsite.
Thebookyouarereadingisactuallyfree—atleast,theinformationinitisfreeto
anyone.Themachine-readablesourcecodeforthebookcomeswithgawk.
Thebookitselfhasgonethroughmultiplepreviouseditions.PaulRubinwrotethevery
firstdraftofTheGAWKManual;itwasaround40pageslong.DianeCloseandRichard
Stallmanimprovedit,yieldingaversionthatwasaround90pagesandbarelydescribed
theoriginal,“old”versionofawk.
Istartedworkingwiththatversioninthefallof1988.Asworkonitprogressed,theFSF
publishedseveralpreliminaryversions(numbered0.x).In1996,edition1.0wasreleased
withgawk3.0.0.TheFSFpublishedthefirsttwoeditionsunderthetitleTheGNUAwk
User’sGuide.SSCpublishedtwoeditionsofthebookunderthetitleEffectiveawk
Programming,andO’Reillypublishedthethirdeditionin2001.
Thiseditionmaintainsthebasicstructureofthepreviouseditions.ForFSFedition4.0,the
contentwasthoroughlyreviewedandupdated.Allreferencestogawkversionspriorto4.0
wereremoved.OfsignificantnoteforthateditionwastheadditionofChapter14.
ForFSFedition4.1(thefourtheditionaspublishedbyO’Reilly),thecontenthasbeen
reorganizedintoparts,andthemajornewadditionsareChapter15andChapter16.
Thisbookwillundoubtedlycontinuetoevolve.Ifyoufindanerrorinthebook,please

reportit!SeeReportingProblemsandBugsforinformationonsubmittingproblemreports
electronically.


HowtoStayCurrent
Youmayhaveanewerversionofgawkthantheonedescribedhere.Tofindoutwhathas
changed,youshouldfirstlookattheNEWSfileinthegawkdistribution,whichprovidesa
high-levelsummaryofthechangesineachrelease.
Youcanthenlookattheonlineversionofthisbooktoreadaboutanynewfeatures.


UsingCodeExamples
Thisbookisheretohelpyougetyourjobdone.Mostoftheexampleprogramsinthis
bookcomeinthegawkdistributionandaremarkedinthefilesasbeinginthepublic
domain.So,ingeneral,youmayusethecodeinthisbookinyourprogramsand
documentation.Incorporatingasignificantamountofproseorexamplecodefromthis
bookintoyourproduct’sdocumentationrequirescompliancewiththeGNUFDL.
Weappreciate,butdonotrequire,attribution.Anattributionusuallyincludesthetitle,
author,publisher,andISBN.Forexample:“EffectiveawkProgramming,FourthEdition,
byArnoldRobbins(O’Reilly).Copyright2015FreeSoftwareFoundation,978-1-49190461-9.”
Ifyoufeelyouruseofcodeexamplesfallsoutsidefairuseorthepermissiongivenhere,
feelfreetocontactusat


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Acknowledgments

TheinitialdraftofTheGAWKManualhadthefollowingacknowledgments:
Manypeopleneedtobethankedfortheirassistanceinproducingthismanual.JayFenlasoncontributedmanyideas
andsampleprograms.RichardMlynarikandRobertChassellgavehelpfulcommentsondraftsofthismanual.The
paperASupplementalDocumentforawkbyJohnW.PierceoftheChemistryDepartmentatUCSanDiego,
pinpointedseveralissuesrelevantbothtoawkimplementationandtothismanual,thatwouldotherwisehave
escapedus.

IwouldliketoacknowledgeRichardM.Stallman,forhisvisionofabetterworldandfor
hiscourageinfoundingtheFSFandstartingtheGNUProject.
Thepreviouseditionofthisbookhadthefollowingacknowledgments:
Thefollowingpeople(inalphabeticalorder)providedhelpfulcommentsonvariousversionsofthisbook:Rick
Adams,Dr.NelsonH.F.Beebe,KarlBerry,Dr.MichaelBrennan,RichBurridge,ClaireCloutier,DianeClose,
ScottDeifik,Christopher(“Topher”)Eliot,JeffreyFriedl,Dr.DarrelHankerson,MichalJaegermann,Dr.RichardJ.
LeBlanc,MichaelLijewski,PatRankin,MiriamRobbins,MarySheehan,andChuckToporek.
RobertJ.ChassellprovidedmuchvaluableadviceontheuseofTexinfo.Healsodeservesspecialthanksfor
convincingmenottotitlethisbookHowtoGawkPolitely.KarlBerryhelpedsignificantlywiththeTeXpartof
Texinfo.
IwouldliketothankMarshallandElaineHartholzofSeattleandDr.BertandRitaSchreiberofDetroitforlarge
amountsofquietvacationtimeintheirhomes,whichallowedmetomakesignificantprogressonthisbookandon
gawkitself.
PhilHughesofSSCcontributedinaveryimportantwaybyloaningmehislaptopGNU/Linuxsystem,notonce,
buttwice,whichallowedmetodoalotofworkwhileawayfromhome.
DavidTruemandeservesspecialcredit;hehasdoneayeomanjobofevolvinggawksothatitperformswelland
withoutbugs.Althoughheisnolongerinvolvedwithgawk,workingwithhimonthisprojectwasasignificant
pleasure.
TheintrepidmembersoftheGNITSmailinglist,andmostnotablyUlrichDrepper,providedinvaluablehelpand
feedbackforthedesignoftheinternationalizationfeatures.
ChuckToporek,MarySheehan,andClaireCloutierofO’Reilly&Associatescontributedsignificanteditorialhelp
forthisbookforthe3.1releaseofgawk.


Dr.NelsonBeebe,AndreasBuening,Dr.ManuelCollado,AntonioColombo,Stephen
Davies,ScottDeifik,AkimDemaille,DarrelHankerson,MichalJaegermann,Jürgen
Kahrs,StepanKasal,JohnMalmberg,DavePitts,ChetRamey,PatRankin,Andrew
Schorr,CorinnaVinschen,andEliZaretskii(inalphabeticalorder)makeupthecurrent
gawk“crackportabilityteam.”Withouttheirhardworkandhelp,gawkwouldnotbenearly
therobust,portableprogramitistoday.Ithasbeenandcontinuestobeapleasureworking
withthisteamoffinepeople.
Notablecodeanddocumentationcontributionsweremadebyanumberofpeople.See
MajorContributorstogawkforthefulllist.
ThankstoAndyOramofO’ReillyMediaforinitiatingthefourtheditionandforhis
supportduringthework.ThankstoJasmineKwitynforhercopyeditingwork.
ThankstoMichaelBrennanfortheForewords.
ThankstoPatriceDumasforthenewmakeinfoprogram.ThankstoKarlBerry,who
continuestoworktokeeptheTexinfomarkuplanguagesane.
RobertP.J.Day,MichaelBrennan,andBrianKernighankindlyactedasreviewersforthe


2015editionofthisbook.Theirfeedbackhelpedimprovethefinalwork.
IwouldalsoliketothankBrianKernighanforhisinvaluableassistanceduringthetesting
anddebuggingofgawk,andforhisongoinghelpandadviceinclarifyingnumerouspoints
aboutthelanguage.Wecouldnothavedonenearlyasgoodajoboneithergawkorits
documentationwithouthishelp.
Brianisinaclassbyhimselfasaprogrammerandtechnicalauthor.Ihavetothankhim
(yetagain)forhisongoingfriendshipandforbeingarolemodeltomeforcloseto30
years!Havinghimasareviewerisanexcitingprivilege.Ithasalsobeenextremely
humbling…
Imustthankmywonderfulwife,Miriam,forherpatiencethroughthemanyversionsof
thisproject,forherproofreading,andforsharingmewiththecomputer.Iwouldliketo
thankmyparentsfortheirlove,andforthegracewithwhichtheyraisedandeducatedme.
Finally,IalsomustacknowledgemygratitudetoG-d,forthemanyopportunitiesHehas

sentmyway,aswellasforthegiftsHehasgivenmewithwhichtotakeadvantageof
thoseopportunities.
[1]The2008POSIXstandardisaccessibleonline.
[2]TheseutilitiesareavailableonPOSIX-compliantsystems,aswellasontraditionalUnix-basedsystems.Ifyouare
usingsomeotheroperatingsystem,youstillneedtobefamiliarwiththeideasofI/Oredirectionandpipes.
[3]Someother,obsoletesystemstowhichgawkwasonceportedarenolongersupportedandthecodeforthosesystems
hasbeenremoved.
[4]OnlySolarissystemsstilluseanoldawkforthedefaultawkutility.Amoremodernawklivesin/usr/xpg6/binon
thesesystems.
[5]GNUstandsfor“GNU’sNotUnix.”