linux_shell_bash

Bash[]developerWorksLinuxBashBashIf:developerWorksBourneagainshell(bash)DanielRobbinsCEO,GentooTechnologies,Inc.20003bashLinuxUNIXDanielRobbinsbashBashbashbashLinuxshellshellbashbashbashbash500KbashbashbashbashCPingshellUNIXbashLinuxshellbashLinuxUNIX--BashbashmanbashbashshellinfobashGNUbashshellbashbashbashbash(1of9)2005-5-2216:22:23BashbashshellASCIIUNIXshellbash“”shellvipwrootEDITORvipwvixemacsvibash$myvar='Thisismyenvironmentvariable!'myvarThisismyenvironmentvariable!=bashbash“”“”bashbash!bashbashbash“”$echo$myvarThisismyenvironmentvariable!$bashmyvarbash“”$echofoo$myvarbarfoofooThisismyenvironmentvariable!barbash$m$my$myvar$myvarbarbash$echofoo${myvar}barfooThisismyenvironmentvariable!bar$myvar${myvar}(2of9)2005-5-2216:22:23Bash“”shellshell“”Cgetenv()C--Cmyvar.c--C#includestdio.h#includestdlib.hintmain(void){char*myenvvar=getenv(EDITOR);printf(Theeditorenvironmentvariableissetto%s\n,myenvvar);}myenv.c$gccmyenv.c-omyenvEDITOR$./myenvTheeditorenvironmentvariableissetto(null)...EDITORC$EDITOR=xemacs$./myenvTheeditorenvironmentvariableissetto(null)myenvxemacs$exportEDITOR$./myenvTheeditorenvironmentvariableissettoxemacsC(3of9)2005-5-2216:22:23Bash$exportEDITOR=xemacsunset$unsetEDITOR$./myenvTheeditorenvironmentvariableissetto(null)dirnamebasenamedirnamebasenameshellshellbashbasenameUNIX$basename/usr/local/share/doc/foo/foo.txtfoo.txt$basename/usr/home/drobbinsdrobbinsBasenamedirnamebasename“”$dirname/usr/local/share/doc/foo/foo.txt/usr/local/share/doc/foo$dirname/usr/home/drobbins//usr/home$MYDIR=`dirname/usr/local/share/doc/foo/foo.txt`$echo$MYDIR/usr/local/share/doc/foo“”Tabbash(4of9)2005-5-2216:22:23Bash$MYDIR=$(dirname/usr/local/share/doc/foo/foo.txt)$echo$MYDIR/usr/local/share/doc/foobash``$()MYFILES=$(ls/etc|greppa)bash-2.03$echo$MYFILESpam.dpasswdbasenamedirname“”bash${MYVAR}bash$MYVAR=foodforthought.jpg$echo${MYVAR##*fo}rthought.jpg$echo${MYVAR#*fo}odforthought.jpg${MYVAR##*fo}${}##(*fo)bashMYVARfoodforthought.jpg*fo##bashfoodforthought.jpg*foffoMATCHES*fofoofoodfoodffoodfoMATCHES*fofoodforfoodfortfoodforthfoodforthofoodforthoufoodforthougfoodforthoughtfoodforthought.jfoodforthought.jpfoodforthought.jpgbash(5of9)2005-5-2216:22:23Bash#--bashbashfofoodforthought.jpg######'#'shift-4$bash$##$“”#$(%)$MYFOO=chickensoup.tar.gz$echo${MYFOO%%.*}chickensoup$echo${MYFOO%.*}chickensoup.tar%%%###*MYFOOD=chickensoup$echo${MYFOOD%%soup}chicken%%%#%345bash$EXCLAIM=cowabunga$echo${EXCLAIM:0:3}cow$echo${EXCLAIM:3:7}abungashelltartar.tarmytar.sh--(6of9)2005-5-2216:22:23Bash#!/bin/bashif[${1##*.}=tar]thenechoThisappearstobeatarball.elseechoAtfirstglance,thisdoesnotappeartobeatarball.fimytar.shchmod755mytar.shtar$./mytar.shthisfile.tarThisappearstobeatarball.$./mytar.shthatfile.gzAtfirstglance,thisdoesnotappeartobeatarball.ifbash=bash${1##*.}1*...tartar1--$1$2ifIfbashifthenelsefiif,elseifif[condition]thenactionficonditionfi(7of9)2005-5-2216:22:23Bashif[condition]thenactionelif[condition2]thenaction2...elif[condition3]thenelseactionxfielifelseif,elif,elsebashbash●developerWorks.●GNU'sbash●bashonlinereferencemanualDanielRobbinsAlbuquerqueGentooGentooTechnologies,Inc.CEOLinuxAdvancedMultimediaProject(LAMP)MacmillanCalderaOpenLinuxUnleashedSuSELinuxUnleashedSambaUnleashedDanielLogoPac-ManSONYElectronicPublishing/[e-mail](8of9)2005-5-2216:22:23Bash(1)(2)(3)(4)(5)developerWorksLinuxIBMIBM(9of9)2005-5-2216:22:23Bash2[]developerWorksLinuxBash2BashforShellwhileuntilCase:developerWorksbashDanielRobbinsCEO,GentooTechnologies,Inc.20004bashDanielRobbinsbashDaniel(if-then)bashbash$1$2$3#!/usr/bin/envbashechonameofscriptis$0echofirstargumentis$1echosecondargumentis$2echoseventeenthargumentis$17echonumberofargumentsis$#$0$#bash$@forBashCPascalPythonPerlifforBashbash(1of9)2005-5-2216:25:25Bash2CCstat()statbash“/tmp/myfile”“$myvar4”bashifif[-z$myvar]thenechomyvarisnotdefinedfi-efilenamefilename[-e/var/log/syslog]-dfilenamefilename[-d/tmp/mydir]-ffilenamefilename[-f/usr/bin/grep]-Lfilenamefilename[-L/usr/bin/grep]-rfilenamefilename[-r/var/log/syslog]-wfilenamefilename[-w/var/mytmp.txt]-xfilenamefilename[-L/usr/bin/grep]filename1-ntfilename2filename1filename2[/tmp/install/etc/services-nt/etc/services]filename1-otfilename2filename1filename2[/boot/bzImage-otarch/i386/boot/bzImage]-zstringstring[-z$myvar]-nstringstring[-n$myvar]string1=string2string1st