Hi vsespb,

as I have to do penance for my sarcastic answer in another thread of today, here my points:

1) You subcommand2.pl test is IMHO a false positive. As soon as you read twice you also get this stuck behaviour. Try this:

open IN, "<&", $ARGV[0] or die $!;
binmode IN;
my $s = <IN>;
print "line: $s";
print "Attempt to read twice:";
$s = <IN>;
print "line: $s";
close IN;
[download]

So, it's the same as subcommand1.pl. You're just kidding yourself.

2) As soon as you modify your main.pl to the following, it works:

use strict;
use warnings;
use IO::Handle;
$^F = 100;

pipe READHANDLE,WRITEHANDLE;
binmode READHANDLE;
binmode WRITEHANDLE;
WRITEHANDLE->autoflush;
READHANDLE->autoflush;
unless (fork()){
        close WRITEHANDLE or die $!;
        exec $^X, $ARGV[0], fileno(READHANDLE);
        die;
}
close READHANDLE or die $!;
print WRITEHANDLE "Test!\n";
close WRITEHANDLE;
wait;
[download]

You see, that the unnecessary ends of the pipe are closed. See http://man7.org/linux/man-pages/man2/pipe.2.html for the description.

Best regards
McA