Depending on your real application, it may be that a dispatch table would serve you well. Consider:

use strict;
use warnings;

my %oss = (linux => \&isLinux, Windows => \&isWindows, undef => \&isOt
+her);
my @array = qw(linux Windows wibble);

exists $oss{$_} ? $oss{$_}->() : $oss{undef}->() for @array;


sub isLinux {
    print "This is linux VM" . "\n";
}

sub isWindows {
    print "This is a Windows VM" . "\n";
}

sub isOther {
    print "I have no idea what it is" . "\n";
}
[download]

Prints:

This is linux VM
This is a Windows VM
I have no idea what it is
[download]