#! /usr/bin/perl

use strict;
use constant DUMMY => 1;
use Socket;
use IO::Handle;

socketpair(CHILD, PARENT, AF_UNIX, SOCK_STREAM, PF_UNSPEC) or die "soc
+ketpair client: $!";

CHILD->autoflush(1);
PARENT->autoflush(1);

if (my $kid = fork) {
    close PARENT;
    for my $key( @ARGV ) {
        print "parent($$) send [$key]\n";
        print CHILD "$key\n";
        chomp(my $line = <CHILD>);
        print "parent($$) recv [$line]\n";
    }
    close CHILD;
    waitpid($kid,0);
}
else {
    die "cannot fork: $!" unless defined $kid;
    close CHILD;
    if( DUMMY ) {
        while( chomp(my $line = <PARENT>) ) {
            print "child($$) recv [$line]\n";
            select undef, undef, undef, 0.2;
            if( rand() < 0.5 ) {
                my $now = "$line " . time;
                print "child($$) send [$now]\n";
                print PARENT "$now\n";
            }
        }
        close PARENT;
    }
    else {
        exec qw{ /bin/foo -c bar } or die "child could not exec: $!\n"
+;
    }
}
[download]

The above works if DUMMY is set to 1 and the kid replies each time. And if I set DUMMY to 0, in order to make the kid exec the program I really want to use it dies with a sullen Broken pipe, and I don't understand why. I know I need a select loop to see if there are handles with data waiting on them, but when I read the man page I feel like a rabbit caught in headlights.

What's more, the code above is for one kid, I need an array of them.