I want to capture STDOUT and STDERR of another process just like I see it when it gets dumped to the terminal (same order).

I wrote a couple test scripts:

outerr.pl
print STDOUT "out 1\n";
print STDOUT "out 2\n";
print STDOUT "out 3\n";

print STDERR "err 4\n";
print STDERR "err 5\n";
print STDERR "err 6\n";

print STDOUT "out 7\n";
print STDOUT "out 8\n";
print STDOUT "out 9\n";

print STDERR "err A\n";
print STDERR "err B\n";
print STDERR "err C\n";

[download]
when run, this script produces the obvious results (all numbers in order).

So I try to capture it all with open3, this way:

use IPC::Open3;
use Symbol;

$OUTERR = gensym();
$IN = gensym();

print STDOUT "running...\n";
$pid = open3($IN, $OUTERR, $OUTERR, 'outerr.pl') or die $!;
while ( wait != $pid ) {};
print STDOUT "done...\n";

while (<$OUTERR>) {
   print STDOUT "got: $_";
}

close OUTERR;

[download]

However, this does not preserve the order. Strangely, in windows, I get all 6 STDOUT's, then all 6 STDERR's - and on unix, I get all 6 STDERR's, then all 6 STDOUT's.

What gives?

In reply to IPC::Open3 confusion by xafwodahs

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