use strict;
use warnings;

my $change = 1;

while (my $plat = <DATA>) {
    chomp $plat;
    print "$plat: ";
    
    if ($plat =~ /[^a-z]/) {
           print "Nothing here.";    
           $change = 0;
    }
    
    if ($change) {
          print "Platform: $plat*";
    }
    
    print "\n";
}

__DATA__
OS/x
os/x
OS/X
win
WIN
Win