Linux操作系统实验.docx

Project1SystemsProgrammingPractice:TheYalnixShellEducationalObjectives:Studentscometothiscoursewithvariousexperiences.Formanypeoplethisprojectwillbepracticeand/orawarmup.Forothers,itW川bealearningexercise.Regardlessofyourbackground,bytheendofthisproject,wehopethatyouwillcomfortablyandconfidentlybeabletodothefollowing: Developclear,readable,well-documentedandwell-designedprogramsintheCProgrammingLanguage. DevelopsoftwareintheUnix/Linuxusingtoolssuchasgcc,gdb,andmake. 1.ocateandinterpreting,manpages"applicabletoapplication-levelsystemprogramming. UsethePOSIX/UnixAPItosystemfunctionstomanageprocessandsessionsaswellasusesignalsandpipesforinter-processcommunication. Understandinghowsynchronizationmightbecomeproblematicinlightofconcurrency. Understandhowtocommunicateandcooperatewithaprojectpartner.ProjectOverviewInthisprojectyouareaskedtoimplementasimplecommand-interpreter,a.k,a."shell,"forLinux.Theshellthatyouwillimplement,knownasysh,shouldbesimilartopopularshellssuchasbash,csh1tcsh1zsh,&c,butitisnotrequiredtoimplementasmanyfeaturesasthesecommercial-gradeproducts.Althoughwedon'trequireallofthe*,bellsandwhistles"thatareincorporatedintocommercial-gradeproducts,yshshouldhavemuchoftheimportantfunctionality: Allowtheusertoexecuteoneormoreprograms,fromexecutablefilesonthefile-system,asbackgroundorforegroundjobs. Providejob-control,includingajoblistandtoolsforchangingtheforeground/backgroundstatusofcurrentlyrunningjobsandjobsuspension/continuation/termination. Allowforthepipingofseveraltasksaswellasinputandoutputredirection.Withrespecttotheotherprogrammingassignmentsthissemester,andmanyothersinyourexperience,thisislikelytobeasmallproject,butwewantyoutoapproachitasifitisabiggerandmorecomplexprojectsothatyouarepreparedfortheremainingprojects.Specifically,we,dlikeyoutodothefollowing: Usethemakeutilitytobuildyourproject Useadebuggerinsteadofprint-ad-huntdebuggingwheneverpractical. Produceclean,well-documented,andwell-designedsolutions.SpecificationFormYoursolutionshouldbeanapplicationprograminvokedwithoutcommand-lineparametersorconfigurationfiles,&c.Ifyouwanttobefancyandsupportforaresourcefilesimilartothoseusedwithcommercial-gradeshells,e.g.cshrc,you,reawelcometodothis.But,likecsh,yourshellshouldfunctioncorrectlyinabsenceofthisfile.1.ook-and-FeelThelookandfeelofyshshouldbeSimilartothatofotherUNIXshells,suchasbash,tcsh,csh,&c.Forexample,yourshell'sworkloopshouldproduceaprompt,e.g.,ysh>,acceptinputfromtheuser,andthenproduceanotherprompt.Messagesshouldbewrittentothescreenasnecessary,andthepromptshouldbedelayedwhenuserinputshouldn,tbeaccepted,asnecessary.Needlesstosay,yourshellshouldtakeappropriateactioninresponsetotheuser'Sinput.InternalCommandsvs.ExternalProgramsInmostcases,theuser*sinputwillbeacommandtoexecuteprogramsstoredwithinafilesystem.We,Ilcalltheseexternalprograms.Yourshellshouldallowtheseprogramstoexecutewithstdinand/orstdoutreassignedtoafile.ItshouldallowprogramsI/Otobechainedtogetherusingpipes.Forourpurposes,acollectionofpipedprocessesorasingleprocessexecutedbyitselffromthecommandlineiscalledajob.Whenexecutingbackgroundsjobs,theshellshouldnotwaitforthejobtofinishbeforeprompting,reading,andprocessingthenextcommand.Whenabackgroundjobfinallyterminatesamessagetothateffectmustbeprinted,bytheshell,totheterminal.Thismessageshouldbeprintedassoonasthejobterminates.Thesyntaxfordoingthiswillbedescribedinthesectionofthisdocumentdescribingtheshell'Sparser.Yourparsershouldalsosupportseveralinterna!commandsthesecommands,ifissuedbytheuser,shoulddirecttheshelltotakeaparticularactionitselfinsteadofdirectingittoexecuteotherprograms.Thedetailsofthisarediscussedinthesectiondescribinginternalcommands.Foregroundvs.BackgroundJobsYourshellshouldbecapableofexecutingbothforegroundandbackgroundjobs.Whereasyourshellshouldwaitforforegroundjobstocompletebeforecontinuing,itshouldimmediatelycontinue,prompttheuser,&c,afterplacingajobintothebackground.CommandlinesWhentheuserrespondstoaprompt,whattheytypecomposesacommandHnestring.Yourshellshouldstoreeachcommand-linestring,untilthejobisfinishedexecuting.Thisincludesbothbackgroundandsuspendedjobs.Theshellshouldassigneachcommand-linestringanon-negativeintegeridentifier.Thedatastructureusedtostorethejobsshouldallowaccesstoeachelementusingthisidentifier.Oncetheactionsdirectedbyacommand-linestringarecompleted,yourshellshouldremoveitfromthedatastructure.Identifierscanberecycledifyouchoose.Pleasenotethatthisdatastructureshouldkeeptrackofwholecommandlinestrings,notjustthenamesoftheindividualtasksthatmaycomposethem.Youshouldnotkeeptrackofcommandlinestringsthatcontaininternalcommands,since,bytheirnature,theywillcompletebeforethisinformationcouldbecomeuseful.InternalCommandsThefollowingaretheinternalcommands.Ifaninternalcommandissubmittedbytheuser,theshellshouldtakethedescribedactionsitself.exit：Killallchildprocessesandexityshwithameaningfulreturncode.jobs：Printoutthecommandlinestringsforjobsthatarecurrentlyexecutingi