switch statement

Perl switch Statement

A switch statement allows a variable to be tested for equality against a list of values. Each value is called a case, and the variable being switched on is checked for each switch case.
A switch case implementation is dependent on Switch module and Switch module has been implemented using Filter::Util::Call and Text::Balanced and requires both these modules to be installed.

Syntax:

The synopsis for a switch statement in Perl programming language is as follows:

use Switch;

switch(argument){

   case 1            { print "number 1" }

   case "a"          { print "string a" }

   case [1..10,42]   { print "number in list" }

   case (\@array)    { print "number in list" }

   case /\w+/        { print "pattern" }

   case qr/\w+/      { print "pattern" }

   case (\%hash)     { print "entry in hash" }

   case (\&sub)      { print "arg to subroutine" }

   else              { print "previous case not true" }

}

The following rules apply to a switch statement:

·         The switch statement takes a single scalar argument of any type, specified in parentheses.

·         The value is followed by a block which may contain one or more case statement followed by a block of Perl statement(s).

·         A case statement takes a single scalar argument and selects the appropriate type of matching between the case argument and the current switch value.

·         If the match is successful, the mandatory block associated with the case statement is executed.

·         A switch statement can have an optional else case, which must appear at the end of the switch. The default case can be used for performing a task when none of the cases is matched.

·         If a case block executes an untargeted next, control is immediately transferred to the statement after the case statement (i.e. usually another case), rather than out of the surrounding switch block.

·         Not every case needs to contain a next. If no next appears, the flow of control will not fall through subsequent cases.

Example:

#!/usr/local/bin/perl

use Switch;

$var = 10;

@array = (10, 20, 30);

%hash = ('key1' => 10, 'key2' => 20);

switch($var){

   case 10           { print "number 100\n" }

   case "a"          { print "string a" }

   case [1..10,42]   { print "number in list" }

   case (\@array)    { print "number in list" }

   case (\%hash)     { print "entry in hash" }

   else              { print "previous case not true" }

}

When the above code is executed, it produces following result:

number 100

Fall-though is usually a bad idea in a switch statement. However, now consider a fall-through case , we will use next to transfer the control to the next matching case which is a list in this case:

#!/usr/local/bin/perl

use Switch;

$var = 10;

@array = (10, 20, 30);

%hash = ('key1' => 10, 'key2' => 20);

switch($var){

   case 10           { print "number 100\n"; next; }

   case "a"          { print "string a" }

   case [1..10,42]   { print "number in list" }

   case (\@array)    { print "number in list" }

   case (\%hash)     { print "entry in hash" }

   else              { print "previous case not true" }

}

When the above code is executed, it produces following result:

number 100

number in list