use strict;
use warnings;

use IPC::Open3;
use IO::Select;
use POSIX ":sys_wait_h";
use Symbol;

my $ERROR=gensym();
my $command="not_a_command";
my ($WRITE, $READ);
my $pid;

$! = undef;
eval {$pid = open3($WRITE, $READ, $ERROR, "$command");};

print "pid is $pid\n" if $pid;

if ($@) {
    print "Trapped error $@";
} elsif (length $!) {
    print "Detected error: $!";
} else {
    print "No error";
}

##</code><code>##

pid is 3412
Detected error: No such file or directory