#! perl -slw
use strict;
use List::Util qw[ reduce ]; $a = $b;

my $zones = reduce {
	my( $first, $last ) = split '-', $b;
	$last ||= $first; ## 1; corrected per [bmann]'s post below.
	substr( $a, $first, $last - $first + 1 ) = 'x' x ( $last - $first + 1 );
	$a
} chr(0) x 1000, split ',', 
'10-374,376-379,382-385,388-499,530-534,541-543,618,619,700-704,707-709';

print $zones =~ m[^.{$_}x] 
    ? "Found $_!" 
    : "$_ isn't there!" 
        for 9, 374, 375, 376, 999;
__END__
[12:03:42.74] P:\test>425464
9 isn't there!
Found 374!
375 isn't there!
Found 376!
999 isn't there!