linux shell-----case statement

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本文探讨了在脚本编程中使用case语句作为多级if-then-else语句的有效替代方案。通过提供具体的语法示例和应用场景，展示了case语句在简化条件判断、提高代码可读性和维护性方面的优势。通过实例演示，读者可以了解如何在实际编程中应用这一技巧。

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The case Statement

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:

#
 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

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.