#! perl -slw use strict; my %pids; for ( 1 .. 2**16 ) { print my $p = open my $cmd, "cmd /c echo $_ |"; 1 while <$cmd>; close $cmd; exists $pids{ $p } and die sprintf "Duplicate $p after %d process starts", keys %pids; $pids{ $p }++; } __END__ Duplicate 3904 after 2632 process starts at C:\test\junk11.pl line 10.