in reply to Re^2: Doubled print with eval and open3
in thread Doubled print with eval and open3

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

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Re^4: Doubled print with eval and open3
by ikegami (Patriarch) on Mar 06, 2007 at 00:52 UTC
    And for FreeBSD 6.1 and Perl 5.8.8, I get 
    pid is 18693
No error

    [download]

    The error occured in the forked child process, so the exec or die would get sent to the file handle piped to $ERROR, and only the child's $! would be affected if the fork succeeded.

    ikegami erases the paragraph he was writting.
    Oo! I just figured it out!

    The OP must be on a system where fork is used ($^O eq 'os2' || $^O eq 'MSWin32' is false). The fork succeeds, but the exec fails. He's getting output from both the child and the parent! Fix: 

    my $pid = eval { open3($WRITE, $READ, $ERROR, "$command") };
if (!$pid) {
   # We're in the child.
   # The fork succeeded, but the exec failed.
   POSIX::_exit($!);
}
...

    [download]

    Update: Oops! Looks like almut beat me to it here

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