You shouldn't use print with select. Had you used sysrwite, I bet it would have returned "successfully wrote 0 bytes" (defined and == 0). In other words, the child had ended. (Well, technically, the child has closed its STDIN, but it did that when it ended.)

Try 

my $msg = "msg\n";

foreach my $w (IO::Select->new($wh)->can_write()) {
    my $rv = syswrite($w, $msg, length($msg));

    if (not defined $rv) {
        die("Unable to send data to child\n");
    }

    if (not $rv) {
        warn("Child is no longer accepting input\n");
        $w_sel->remove($w);
        next;
    }

    if ($rv != length($msg)) {
        warn("Pipe is full. We'd normally call select again\n");
        next;
    }

    print "Successfully sent message to the child\n";
}

[download]

Don't forget to reap your children with waitpid.

In reply to Re: Pipes and IO::Select's method can_write() by ikegami
in thread Pipes and IO::Select's method can_write() by almut

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