#-----
# handle SIGPIPE ourselves, so we don't get killed
$SIG{PIPE} = sub { warn "BROKEN PIPE\n" };

if (my ($w) = IO::Select->new($wh)->can_write()) {
    if (print $w "$msg\n") {
        print "wrote '$msg' to $w ('| @cmd')\n";
        close $w;
    } else {
        warn "print to $w FAILED\n";
        # we'll have gotten a SIGPIPE, too
    }
} else {
    warn "$wh not ready for writing\n";
}
#-----