Hmm, interesting. I ran OP's code under a debugger as a learning exercise, and thought I'd inferred the problem. Maybe I just found a different one:

If that's true, why is "Error, Could not executed" printed.

On Windows it's not - there's a clue right there! Actually on Windows the OP's sample code just prints a comma. The following:

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";
}

[download]

prints:

pid is 3412
Detected error: No such file or directory

[download]

on Windows.

DWIM is Perl's answer to Gödel

In reply to Re^3: Doubled print with eval and open3 by GrandFather
in thread Doubled print with eval and open3 by jlm17

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