small getopts tutorial

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1、SmallgetoptstutorialincompleteWhenyouwanttoparsecommandlineargumentsinaprofessionalway,getoptsisthetoolofchoice.Unlikeitsolderbrothergetopt(notethemissings!),it'sashellbuiltincommand.Theadvantageisyoudon'tneedtohandyourpositionalparametersthroughtoanext

2、ernalprogramgetoptscaneasilysetshellvariablesyoucanuseforparsing(impossibleforanexternalprocess!)youdon'thavetoarguewithseveralgetoptimplementationswhichhadbuggyconceptsinthepast(whitespaces,…)getoptsisdefinedinPOSIX®Someothermethodstoparsepositionalpar

3、ameters(withoutgetopt(s))aredescribedin:Howtohandlepositionalparameters.NotethatgetoptsisnotabletoparseGNU-stylelongoptions(--myoption)orXF86-stylelongoptions(-myoption)!DescriptionTerminologyIt'susefultoknowwhatwe'retalkingabouthere,solet'ssee…Consider

4、thefollowingcommandline:mybackup-x-f/etc/mybackup.conf-r./foo.txt./bar.txtAllthesearepositionalparameters,butyoucandividethemintosomelogicalgroups:-xisanoption,aflag,aswitch:onecharacter,indroducedbyadash(-)-fisalsoanoption,butthisoptionhasanadditionala

5、rgument(argumenttotheoption-f):/etc/mybackup.conf.Thisargumentisusuallyseparatedfromitsoption(byawhitespaceoranyothersplittingcharacter)butthat'snotamust,-f/etc/mybackup.confisvalid.-rdependsontheconfiguration.Inthisexample,-rdoesn'ttakearguments,soit's

6、astandaloneoption,like-x./foo.txtand./bar.txtareremainingargumentswithoutanyoptionrelated.Theseoftenareusedasmass-arguments(likeforexamplethefilenamesyouspecifyforcp(1))orforargumentsthatdon'tneedanoptiontoberecognizedbecauseoftheintendedbehaviourofthep

7、rogram(likethefilenameargumentyougiveyourtext-editortoopenanddisplay-whywouldoneneedanextraswitchforthat?).POSIX®callsthemoperands.Togiveyouanideaaboutwhygetoptsisuseful:Theabovecommandlinecouldalsoreadlike…mybackup-xrf/etc/mybackup.conf./foo.txt./bar.t

8、xt…whichisveryhardtoparsebyowncode.getoptsrecognizedallthecommonoptionformats.Theoptionflagscanbeupper-andlowercasecharacters,andofcoursedigits.Itmayrecognizeothercharacters,butthat'snotrecommended(usabilityandmaybeproblemswithsp