Linux操作系统实验.docx

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1、Project1SystemsProgrammingPractice:TheYalnixShellEducationalObjectives:Studentscometothiscoursewithvariousexperiences.Formanypeoplethisprojectwillbepracticeand/orawarmup.Forothers,itW川bealearningexercise.Regardlessofyourbackground,bytheendofthisproject,wehopethatyouwillcomfortablyandconfidentlybeabl

2、etodothefollowing: Developclear,readable,well-documentedandwell-designedprogramsintheCProgrammingLanguage. DevelopsoftwareintheUnix/Linuxusingtoolssuchasgcc,gdb,andmake. 1.ocateandinterpreting,manpagesapplicabletoapplication-levelsystemprogramming. UsethePOSIX/UnixAPItosystemfunctionstomanageprocess

3、andsessionsaswellasusesignalsandpipesforinter-processcommunication. Understandinghowsynchronizationmightbecomeproblematicinlightofconcurrency. Understandhowtocommunicateandcooperatewithaprojectpartner.ProjectOverviewInthisprojectyouareaskedtoimplementasimplecommand-interpreter,a.k,a.shell,forLinux.T

4、heshellthatyouwillimplement,knownasysh,shouldbesimilartopopularshellssuchasbash,csh1tcsh1zsh,&c,butitisnotrequiredtoimplementasmanyfeaturesasthesecommercial-gradeproducts.Althoughwedontrequireallofthe*,bellsandwhistlesthatareincorporatedintocommercial-gradeproducts,yshshouldhavemuchoftheimportantfun

5、ctionality: Allowtheusertoexecuteoneormoreprograms,fromexecutablefilesonthefile-system,asbackgroundorforegroundjobs. Providejob-control,includingajoblistandtoolsforchangingtheforeground/backgroundstatusofcurrentlyrunningjobsandjobsuspension/continuation/termination. Allowforthepipingofseveraltasksas

6、wellasinputandoutputredirection.Withrespecttotheotherprogrammingassignmentsthissemester,andmanyothersinyourexperience,thisislikelytobeasmallproject,butwewantyoutoapproachitasifitisabiggerandmorecomplexprojectsothatyouarepreparedfortheremainingprojects.Specifically,we,dlikeyoutodothefollowing: Usethe

7、makeutilitytobuildyourproject Useadebuggerinsteadofprint-ad-huntdebuggingwheneverpractical. Produceclean,well-documented,andwell-designedsolutions.SpecificationFormYoursolutionshouldbeanapplicationprograminvokedwithoutcommand-lineparametersorconfigurationfiles,&c.Ifyouwanttobefancyandsupportforareso

8、urcefilesimilartothoseusedwithcommercial-gradeshells,e.g.cshrc,you,reawelcometodothis.But,likecsh,yourshellshouldfunctioncorrectlyinabsenceofthisfile.1.ook-and-FeelThelookandfeelofyshshouldbeSimilartothatofotherUNIXshells,suchasbash,tcsh,csh,&c.Forexample,yourshellsworkloopshouldproduceaprompt,e.g.,

9、ysh,acceptinputfromtheuser,andthenproduceanotherprompt.Messagesshouldbewrittentothescreenasnecessary,andthepromptshouldbedelayedwhenuserinputshouldn,tbeaccepted,asnecessary.Needlesstosay,yourshellshouldtakeappropriateactioninresponsetotheuserSinput.InternalCommandsvs.ExternalProgramsInmostcases,theu

10、ser*sinputwillbeacommandtoexecuteprogramsstoredwithinafilesystem.We,Ilcalltheseexternalprograms.Yourshellshouldallowtheseprogramstoexecutewithstdinand/orstdoutreassignedtoafile.ItshouldallowprogramsI/Otobechainedtogetherusingpipes.Forourpurposes,acollectionofpipedprocessesorasingleprocessexecutedbyi

11、tselffromthecommandlineiscalledajob.Whenexecutingbackgroundsjobs,theshellshouldnotwaitforthejobtofinishbeforeprompting,reading,andprocessingthenextcommand.Whenabackgroundjobfinallyterminatesamessagetothateffectmustbeprinted,bytheshell,totheterminal.Thismessageshouldbeprintedassoonasthejobterminates.

12、ThesyntaxfordoingthiswillbedescribedinthesectionofthisdocumentdescribingtheshellSparser.Yourparsershouldalsosupportseveralinterna!commandsthesecommands,ifissuedbytheuser,shoulddirecttheshelltotakeaparticularactionitselfinsteadofdirectingittoexecuteotherprograms.Thedetailsofthisarediscussedinthesecti

13、ondescribinginternalcommands.Foregroundvs.BackgroundJobsYourshellshouldbecapableofexecutingbothforegroundandbackgroundjobs.Whereasyourshellshouldwaitforforegroundjobstocompletebeforecontinuing,itshouldimmediatelycontinue,prompttheuser,&c,afterplacingajobintothebackground.CommandlinesWhentheuserrespo

14、ndstoaprompt,whattheytypecomposesacommandHnestring.Yourshellshouldstoreeachcommand-linestring,untilthejobisfinishedexecuting.Thisincludesbothbackgroundandsuspendedjobs.Theshellshouldassigneachcommand-linestringanon-negativeintegeridentifier.Thedatastructureusedtostorethejobsshouldallowaccesstoeachel

15、ementusingthisidentifier.Oncetheactionsdirectedbyacommand-linestringarecompleted,yourshellshouldremoveitfromthedatastructure.Identifierscanberecycledifyouchoose.Pleasenotethatthisdatastructureshouldkeeptrackofwholecommandlinestrings,notjustthenamesoftheindividualtasksthatmaycomposethem.Youshouldnotk

16、eeptrackofcommandlinestringsthatcontaininternalcommands,since,bytheirnature,theywillcompletebeforethisinformationcouldbecomeuseful.InternalCommandsThefollowingaretheinternalcommands.Ifaninternalcommandissubmittedbytheuser,theshellshouldtakethedescribedactionsitself.exit：Killallchildprocessesandexityshwithameaningfulreturncode.jobs：Printoutthecommandlinestringsforjobsthatarecurrentlyexecutingi