#!/usr/bin/perl

my $cmd = 'echo my PID is $$ && ./pid.pl';
my $pid = open PID, "| $cmd"
    or die "Can't run ./pid.pl: $!\n";

print "PID returned by open: $pid\n";
sleep 2;
__END__
my PID is 4465
PID returned by open: 4465
./pid.pl PID : 4466