def Wget(src_url, tgt_name, tgt_root=None):
    """
    Download url, if required.

    Args:
        src_url (str): Our SOURCE url.
        tgt_name (str): The filename we want to have on disk.
        tgt_root (str): The TARGET directory for the download.
            Defaults to ``CFG["tmpdir"]``.
    """
    if tgt_root is None:
        tgt_root = str(CFG["tmp_dir"])

    from benchbuild.utils.cmd import wget

    tgt_file = local.path(tgt_root) / tgt_name
    if not source_required(tgt_file):
        Copy(tgt_file, ".")
        return

    wget(src_url, "-O", tgt_file)
    update_hash(tgt_file)
    Copy(tgt_file, ".")