Here is a demonstration of how to set up a pipeline like the one that you want which will give you the pid of the first process in the pipeline. Note that it is slightly complex and is easy to get wrong (I'm going out of my way to make sure that Perl spawns no shells to interpret shell commands): 
#! /usr/bin/perl
use strict;
use IPC::Open2;

local *PIPE;
local *OUT;
my $pid = open(PIPE, "-|", "echo", "hi") or die "Can't echo: $!";
print "The pid of the echo command is: $pid";
<STDIN>;
open2(\*OUT, "<&PIPE", "perl", "-ne", "print uc")
  or die "open2 failed: $!";
print while <OUT>;

[download]
You can use ps to verify that before you tie the two programs together the pid that you got from open actually is the pid of the echo process that you launched.

UPDATE: I left out the assignment to pid. Added. (I had included an earlier version of the code, then commented about a later one that demonstrated the pid, then partially updated the code but missed one line. My apologies for any confusion.)

In reply to Re: Taming multiple external processes by tilly
in thread Taming multiple external processes by 87C751

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