Perl switch Statement

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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.

Flow Diagram

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 the 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 the 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 the following result −

number 100
number in list