Perl!

#!/usr/bin/perl

use strict;
use warnings;

my $ex1 = '#S(5,Hello)';

$ex1 =~ /\#S\((\d+),(\w*)\)/;

if ($1 == length($2)) {
    print "match\n";
} else {
    print "does not match\n";
}

Essentially just extract the number and the text in subpatterns, then compare them.