use strict;
use warnings;

use Fcntl qw( F_GETFD F_SETFD FD_CLOEXEC );
use POSIX qw( dup2 );

sub keep_open_on_exec {
   my ($fh) = @_;
   my $flags = fcntl($fh, F_GETFD, 0);
   next if $flags & FD_CLOEXEC == 0;
   fcntl($fh, F_SETFD, $flags & ~FD_CLOEXEC);
}

open(my $src1_fh, '-|', echo => 'apples')
   or die("open: $!");
open(my $src2_fh, '-|', echo => 'oranges')
   or die("open: $!");

keep_open_on_exec($_) for $src1_fh, $src2_fh;

system(diff => '/dev/fd/'.fileno($src1_fh), '/dev/fd/'.fileno($src2_fh)) >= 0
   or die("system: $!");

printf("\$?=%04X\n", $?);