open my $datafile ... 
LINE:
while ( my $line = <$file> ) {
    next LINE unless length $line;
    next LINE if ( $line =~ m{\A \s* #}xms;
    process $line;
}

##</code><code>##

if ( option_A( $line ) ) {
   $retval = do_this_complicated_thing( $line );
}
elsif ( option_B( $line ) {
   retval = 'alphagetti';
   retval .= ' and maple syrup' 
      if $option_C( $line );
}
else {
    $retval = 42;
}
return $retval;