The following paper was originally published in the Proceedings of the Fifth Annual Tcl/Tk Workshop Boston, Massachusetts, July 1997 TclOSAScript - Exec for MacTcl Jim Ingham Lucent Technologies (now at Sun Microsystems) Raymond Johnson Sun Microsystems For more information about USENIX Association contact: 1. Phone: 510 528-8649 2. FAX: 510 548-5738 3. Email: [email protected] 4. WWW URL: http://www.usenix.org TclOSAScript-ExecforMacTcl JimIngham LucentTechnologies (nowatSunMicrosystems) [email protected] RaymondJohnson SunMicrosystems [email protected] Abstract: WedescribetheTclOSAScriptextensiontoMacTcl.TclOSAScriptprovides theabilityforMacTclscriptstorunscriptsinanyotherOSAcompatible languageontheMacintosh.SincetheOSAisthestandardmechanismfor interapplicationcommunicationontheMac,thisallowsMacTcltorunother applications,andprovidesanexeclikefacility(thougharguablyusingamuch richercommunicationmodel.) I) AnIntroductiontotheOpen Tk95and96conferences[3,4].Therearetwo ScriptingArchitecture implementationsofthissolutionthathavebeen presented.TedBeldungwroteaextensioncalled Theusualinterapplicationcommunicationmecha- ASTcl[5]whichonlyworkedwithAppleScript,and nismforUnixbasedtoolsreliesonthesimpleex- didnotusemanyoftheadvancedfeaturestheOSA pedientofconnectingthestandardinandstan- offers.TclOSAScript,whichwasdevelopedcon- dardoutchannelsofthespawnedprocesstochan- currently,isamorecompleteimplementation.This nelsoftheparentprocess.Thecommunication istheonewewilldetailinthispaper. betweentheparentandchildprocessesthenmim- ThereisarealproblemthattheOSAaimstosolve icstheuserinteractionwiththeprocess,namely aswell–beyondthefactthattheremaywellnot typingcommandsonthecommandline.The beatextbasedcommandinterfacetotasksina “exec”commandinTcl,aswellastheopen-with- modernGUIoperatingsystem.Forwhilethecom- pipecommand,usethismechanismtogiveTclac- mand-basedformofcommunicationiseasyto cesstoprocessesinthesurroundingsystem. implement,toactuallydriveanapplicationyou Thismethod,unfortunately,isinapplicableon needtoknowtheparticularlanguagethattheap- Macintoshsystems.Macintoshapplicationsare plicationuses,beitsimplecommandlineswitches, onlyimplementedwithaGraphicalUserInterface orareallanguagesuchasTcl.Thereisnogeneric (GUI).Thereisnocommandline,andthusno waytoexposethefunctionalelementsofanappli- conceptofstandardinandstandardout.How- cationwithouttyingthemtoaparticularscripting ever,thisdoesnotmeanthereisnointerapplication language. communicationmechanism.Instead,amuchricher Thesolutionistodefinethebasicobjectsandverbs methodofscriptingexternaltasksisprovidedby thattheapplicationsupportsinalanguageneutral theOpenScriptingArchitecture(OSA)[1,2]. way.Thenthescriptinglanguagemustprovidea Thisproblem,andtheOSAsolutionpresentedhere, mechanismforqueryingouttheseelements.Fi- werefirstmentionedinpapersintheUsenixTcl/ nally,theoperatingsystemwillprovideamessag- ingsystemthatwillallowanyscriptinglanguage OneapplicationundertheMacOSsendsanApple todrivetheobjectsofthetargetapplication. Eventtoanotherapplicationbybuildingupthe AppleEventdatastructure,andthenpassingitto theAppleEventManager,whichplacestheevent a)SpecificationofVerbs&Objects–theaete intheeventqueueofthetargetapplication.The Thespecificationofobjectsisachievedwiththe targetapplicationthenhandlesthiseventbypars- AppleEventTerminologyExtension.Thisisaresource ingupitscontentsandperformingtherequired intheresourceforkoftheapplicationwhichlists task. the‘events’towhichtheapplicationresponds,and theclassesofobjectsintheapplication. c)OSAcompliantlanguages Examplesofeventsthatanapplicationmightrec- Allinterapplicationcommunicationiscarriedout, get set create ognizearethe‘ ’,‘ ’and‘ ’events, underthehood,bytheexchangeofAppleEvents. whichjustprovideaccesstotheobjectsintheap- However,thisistoolowlevelanexchangemecha- plication.Theseformpartofthe“StandardSuite” nismtobeusefultotheaverageuser. ofcommandsthatallwelldesignedOSAapplica- tionsshouldsupport.Therearealsomorespecial- ThejobofanOSAcompliantlanguage,then,isto izedverbs,suchas‘select’or‘revert’inaWord wrapamorehumansyntaxaroundtheconstruc- Processorappor‘ download’and‘ view file tionoftheAppleEventmessages.Theapproved list’intheFTPclientapplicationFetch.Events methodfordoingthisistoreadtheaeteofatarget alsotakeparameters,suchaswhichwordtoselect application,andimporttheverbsandnounsfound inawordprocessor,orwhichfiletodownloadin thereinintoitsownsyntaxinanaturalway.Done Fetch. thisway,theaetecanserveasdocumentationfor howtoscripteachlanguage,andthelanguagecan Examplesofobjectsarethewindowsofanapplica- dynamicallyappropriatenewapplicationsasthey tion,orthewordsandparagraphsinawordpro- areencountered. cessorwindow.Thereisalsoawayofspecifyinga containmenthierarchy,soeachobjectcanbecon- OfthetwomajorOSAcompliantlanguages,only tainedinotherobjects,andcancontainotherob- AppleScript[6]dynamicallyreadstheaeteofthe jects,.Finally,theobjectsmaytakequalifiers.An targetapplication.UserLandFrontier[7]hasastatic exampleofamoderatelycomplicatedobjectspeci- gluetableforeachapplicationthatrelatestheevent fier,inAppleScriptdialect,is:“ the file andobjectcodeswithcommandsintheFrontier “mactcltk-full-8.0a2” in the transfer language.Thislimitsthenumberofscriptableap- window “ftp.sunlabs.com” of the appli- plicationsthatFrontiercanactuallydrive. cation “Fetch 3.0.2””. Theaetemakestheconnectionbetweenthetext d)OSAComponents phrasewhichspecifiesanobjectorverb,andsome ThefinalpartoftheOSAarchitectureistheOSA packed4charactercodewhichwilloccurinthe component.Thisisanimplementationoftheno- compiledformoftheinterapplicationmessages.It tionthatascriptinglanguageisnotsomuchapart alsospecifiestheparametersfortheverbs(with oftheapplication,asaservicethatisprovidedto thenotionofrequiredandoptionalparameters), applications,toaidtheminexposingtheiropera- andthecontainmenthierarchyoftheobjects.Once tiveparts. youknowtheaeteofanapplication,youknowthe formanymessagetothatapplicationmusttake. Tclhasbeenverysuccessfulpreciselybecauseit makesiteasytobindtogetherthefunctionalele- b)TheMessagingsystem–AppleEvents mentsoftheapplicationwithouthavingto recompiletheapplication.ButtomakeuseofTcl, ThemessagingsystemintheOSAisgovernedby theapplicationmustembedaTclinterpreterwithin theAppleEventManager.AnAppleEventisa theobjectcodeoftheapplication.Thistiesthe datastructurethatdescribesaneventintermsof useoftheapplicationtoTcl;youcannotdynami- theaforementionedpacked4charactercodes.It callychoosewhichscriptinglanguageyouwantto startswiththemainverb,andthenusuallyhasa employ. directobjectwithitsqualifiers,andperhapsother parameters.AppleEventssupportnesting,sothat TheOSAgoesfurthertomaketheoperatingsys- asingleeventcansupportrecursiveevaluation temthemanagerofscriptingsolutions.Thepro- (muchlikethe[]syntaxinTcl). viderofascriptinglanguagewritessomegluecode thatregistersthescriptinglanguagewiththeoper- atingsystem.Applicationsrequestaconnectionto atedbythatcomponent.Currentlyconnections thescriptingcomponent,andthensendscriptdata tobothofthepopularOSAlanguages,AppleScript tothatcomponenttobeevaluated.Thescriptdata andUserLandFrontierhavebeentested. canevencontaintagsidentifyingitslanguage,so TclOSAScriptwillbeincludedasashareablelibrary thattheapplicationcanreceivescriptingdatain inthe8.0releaseofMacTcl.Whatfollowsisa anyoftheavailablelanguages,passittotheOSA generaldescriptionoftheTclOSAScriptextension. componentmanager,whichwillinturnrouteitto theappropriatecomponent. 1)TheOSAcommand Thisconnectioncanbeusedintwoways.Oneis ThefirststepinusinganyOSAcomponentisto toallowanapplicationtodriveotherapplications, getaconnectiontoaninstanceofthecomponent. sothatitdoesnothavetoduplicatetheirfunc- Atstartup,TclOSAScriptscansthelistofOSAcom- tionality.AgoodexampleofthisistheMicroSoft ponents,opensaconnectiontoeachonethatis InternetExplorer,whichhandsoffe-mail,FTPand found,andcreatesaTclcommandtoaccessthat NNTPrequeststotheuser’sfavoritee-mail,FTP component.SoiftheuserhasAppleScriptinstalled andUsenetclientsusingtheOSA. ontheirmachine,anAppleScriptcommandwill AdeeperuseoftheOSAisto“factor”theuser becreated.IfUserLandFrontierisrunningat interfaceelementsoftheapplicationfromitscore startup,a UserLand commandwillbecreated, functionality.Theuserinterfaceelementsdonot andsoon. directlycallthesubroutinesthatdotheworkof Thereisalsoagenericcommand, OSA,thatwill theapplication.RathertheysendAppleEventsback allowotherconnectionstobeopened,orclosed, totheapplication,whichreceivestheseevents,and andwillallowtheusertoquerythelistofcompo- thendispatchesthemtotheappropriateinternal nents.Thisisuseful,forinstance,toopenconnec- routines. tionswithotherlanguages. Theadvantageofthisisthatyoucanthen“attach” Anexampleofthisuseiscommunicationwiththe scriptstotheUIelements,whichscriptsdothe UserLandlanguage.TheUserLandOSAcompo- workofdispatchingtheAppleEvents.Thisimme- nentisinstalledonlywhiletheFrontierapplica- diatelyprovidesanarchitecturemuchlike tionisrunning.SoifyouwantedtouseFrontier, HyperCard,ortheTcl/Tkcallbacks,butwiththe youcouldopenit(byusingtheAppleScriptcom- addedbenefitthatthecallbacklanguageisleftup mand),andthenusetheOSAcommandtoopena totheuser’sdiscretion. connectiontotheUserLandcomponent... Itiscurrentlynotusefultoopenmultipleconnec- II) TclandtheOSA tionstothesamecomponent.Sincethecallsto theOSAcomponentsaresynchronous,havingsev- eralconnectionstoasingleOSAcomponentdoes TherearethreestepstofitTclintotheOSAarchi- notgainanything. tecture.ThefirstistoallowTcltousetheservices offeredbytheOSAcomponentsinstalledonthe system.ThisisthefunctionoftheTclOSAScript 2)CompilingandExecutingScripts: extensionwhichisdescribedintherestofthispa-