You can use IPC::Open3 to achieve bi-directional communication with child.
use strict;
use IPC::Open3;
my $pid = open3(\*CHLD_IN, \*CHLD_OUT, \*CHLD_ERR, 'cat')
or die "open3() failed $!";
my $r;
for(my $i=1;$i<10;$i++) {
print CHLD_IN "$i\n";
$r = <CHLD_OUT>;
print "Got $r from child\n";
}