$cmd="$scriptsdir/process_tar.pl $file >> /tmp/testlog &";                      
+                  
$pid=open(PID,"|$cmd");

##</code><code>##

#!/usr/bin/perl
# file pid.pl
sleep 1; print "$0 PID: $$\n";

##</code><code>##

#!/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