open3example.pl

#!/usr/bin/perl
use strict;
use IPC::Open3;
use IO::Select;

my $child_pid = open3(*W, *R, *E, "/usr/bin/yes");
close (W);

my ($selector) = IO::Select->new();
$selector->add (*R, *E);

my $l = 0;
while (1) {
    last if scalar ($selector->handles) == 0;
    my @ready = $selector->can_read (1);
    for my $fh (@ready) {
        my $ffh = fileno($fh);
        if (eof ($fh)) {
            $selector->remove ($fh);
            next;
        }
        my $line = scalar <$fh>;
        chomp $line;
        $l++;
        if ($ffh == fileno(R)) {
        } elsif ($ffh == fileno (E)) {
        }
        print "$l\n" if $l =~ /00000$/;
    }
}
close(R);
close(E);