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

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

##</code><code>##

open IN, "<&", $ARGV[0] or die $!;
binmode IN;
while(defined($_ = <IN>)) {
    print "line $_";
}
close IN;

##</code><code>##

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

##</code><code>##

perl main.pl subcommand1.pl

##</code><code>##

perl main.pl subcommand2.pl

##</code><code>##

cat subcommand1.pl | perl subcommand1.pl 0