use strict;
use warnings;

my $rxInput = qr
   {(?x)
      ^
      (
         h(?:s(?:b(?:n)?)?)?
         |
         a(?:d(?:m(?:i(?:n)?)?)?)?
      )
      $
   };

print "What network? ";
my $resp;
chomp($resp = <STDIN>);
print "Invalid response\n" unless $resp =~ $rxInput;

# Do something here with $1
...