When Getopt::Long says "requires a value" what it says is that if blah occurs it must have a value, not that blah is required. If you run your script with -blah (no value given) you will see $result is undef.

I am afraid what you will have to do is check blah is set once you have eaten up the options.

use strict;
use warnings;
use Getopt::Long;
{
    my $blah;
    my $result = GetOptions('blah=i'    =>  \$blah);

    &usage unless $blah;
    print "result = $result\n";
    print "blah = $blah\n";
}
sub usage {
    print "$0: -blah=value\n"
}
[download]

Cheers,
R.