my $OS;
if ($^O =~ /mswin/i) {$OS = "Windows";print "OS detected: Windows\n"}
elsif ($^O =~ /linux/i) {$OS = "Linux";print "OS detected: Linux\n"}
elsif ($^O =~ /darwin/i) {$OS = "Mac";print "OS detected: Mac OS X\n"} 
else {print "\nUnable to detect OS type, choose your OS:\n\nWindows	Any version of Microsoft Windows\nMac	Any flavour of Mac OS X\nLinux	Linux of some sort\n\n";
do {
chomp ($OS = <STDIN>);
print "\nIncorrect OS type. Try again.\n\n" unless $OS eq "Windows" or $OS eq "Mac" or $OS eq "Linux";} until ($OS eq "Windows" or $OS eq "Mac" or $OS eq "Linux");
}