Perl AnyEvent: How to make async calls in a loop?

gistfile1.pl

#!/usr/bin/perl

use strict;
use warnings;
use v5.10;
use AnyEvent;
use AnyEvent::Util;


# OBS: This doesn't work!

for my $n (1..100) {
    my $rand = int(rand(10));
    my $hdl;
    $hdl = AnyEvent::io (
        fh => \*STDIN,
        poll => 'r',
        cb => sub {
            my $str = `sleep $rand; echo $n`;
            output($str);
        }
     );
}

# Hmm - args
sub output {
    my $n = shift;
    say "Got: $n";
}
__END__

perl testAny.pl 
illegal file descriptor or filehandle (either no attached file descriptor or illegal value):  at /usr/local/lib64/perl5/AnyEvent/Impl/EV.pm line 55.