my $string = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
my ($random) = $string =~ m/(??{'.'x rand length $string })(.)/s;
print $random, "\n";

##</code><code>##

my $string = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
my( $random ) = $string =~ m/^(??{ '.' x rand length $_ })(.)/s;
print "$random\n";

##</code><code>##

my $string = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
my ($random) = $string =~ m/^
                            (??{'.{' . int(rand length $_) . '}' })
                            (.)
                           /sx;
print "$random\n";