my $err_code = system 'wget', '-q', -O', $FILENAME, $URL;
if ($err_code) {
    if ($err_code == 1) { EXIT(-1, "wget: Generic error code") }
    elsif ($err_code==2) { EXIT(-1, "wget: Parse error (cmdline, .wgetrc, ...)") }
    elsif ($err_code==3) { EXIT(-1, "wget: File I/O error") }
    ... etc. ...
}