Question

Is there a neat way of making a case or switch statement in Perl 5?. It seems to me they should include a switch on version 6.

I need this control structure in a script, and I’ve heard you can import a "switch module". But how can I achieve it without imports to minimize dependencies and acquire portability?

Answer 1

If you are using Perl 5.10 you have given/when which is a switch statement (note, it can do more than compare with regexes, read the linked docs to see its full potential):

#or any of the dozen other ways to tell 5.10 to use its new features
use feature qw/switch/; 

given($string) {
    when (/^abc/) { $abc     = 1; }
    when (/^def/) { $def     = 1; }
    when (/^xyz/) { $xyz     = 1; }
    default       { $nothing = 1; }
}

If you are using Perl 5.8 or earlier you must make do with if/elsif/else statements:

if    ($string =~ /^abc/) { $abc     = 1; }
elsif ($string =~ /^def/) { $def     = 1; }
elsif ($string =~ /^zyz/) { $xyz     = 1; }
else                      { $nothing = 1; }

or nested condition operators (?:):

$string =~ /^abc/ ? $abc     = 1  :
$string =~ /^def/ ? $def     = 1  :
$string =~ /^xyz/ ? $xyz     = 1  :
                    $nothing = 1;

There is a module in Core Perl (Switch) that gives you fake switch statements via source filters, but it is my understanding that it is fragile:

use Switch;

switch ($string) {
    case /^abc/ {
    case /^abc/ { $abc     = 1 }
    case /^def/ { $def     = 1 }
    case /^xyz/ { $xyz     = 1 } 
    else        { $nothing = 1 }
}

or the alternate syntax

use Switch 'Perl6';

given ($string) {  
    when /^abc/ { $abc     = 1; }
    when /^def/ { $def     = 1; }
    when /^xyz/ { $xyz     = 1; }
    default     { $nothing = 1; }
}