case..esac..in Linux Shell Script

The case statement is good alternative to Multilevel if-then-else-fi statement. It enable you to match several values against one variable. Its easier to read and write.

Syntax:

           case  $variable-name  in
                pattern1)   command
                                ...
                                ..
                                command;;
                pattern2)   command
                                ...
                                ..
                                command;;
                patternN)   command
                                ...
                                ..
                                command;;
                *)             command
                                ...
                                ..
                                command;;
           esac

The $variable-name is compared against the patterns until a match is found. The shell then executes all the statements up to the two semicolons that are next to each other. The default is *) and its executed if no match is found. For e.g. write script as follows:

$ cat > car # # if no vehicle name is given # i.e. -z $1 is defined and it is NULL # # if no command line arg

if [ -z $1 ] 
        then 
          rental="*** Unknown vehicle ***" 
        elif [ -n $1 ] 
        then 
        # otherwise make first arg as rental 
          rental=$1 
        fi
	case $rental in 
           "car") echo "For $rental Rs.20 per
        k/m";; 
           "van") echo "For $rental Rs.10 per
        k/m";; 
           "jeep") echo "For $rental Rs.5 per
        k/m";; 
           "bicycle") echo "For $rental 20 paisa
        per k/m";; 
           *) echo "Sorry, I can not gat a $rental for
        you";; 
        esac

Save it by pressing CTRL+D and run it as follows:

$ chmod +x car $ car van $ car car $ car Maruti-800

First script will check, that if $1(first command line argument) is given or not, if NOT given set value of rental variable to "*** Unknown vehicle ***",if command line arg is supplied/given set value of rental variable to given value (command line arg). The $rental is compared against the patterns until a match is found. For first test run its match with van and it will show output "For van Rs.10 per k/m." For second test run it print, "For car Rs.20 per k/m". And for last run, there is no match for Maruti-800, hence default i.e. *) is executed and it prints, "Sorry, I can not gat a Maruti-800 for you". Note that esac is always required to indicate end of case statement.