def version_cmp(pkg1, pkg2, **kwargs):
    '''
    Do a cmp-style comparison on two packages. Return -1 if pkg1 < pkg2, 0 if
    pkg1 == pkg2, and 1 if pkg1 > pkg2. Return None if there was a problem
    making the comparison.

    CLI Example:

    .. code-block:: bash

        salt '*' pkg.version_cmp '0.2.4-0' '0.2.4.1-0'
    '''
    # ignore_epoch is not supported here, but has to be included for API
    # compatibility. Rather than putting this argument into the function
    # definition (and thus have it show up in the docs), we just pop it out of
    # the kwargs dict and then raise an exception if any kwargs other than
    # ignore_epoch were passed.
    kwargs = salt.utils.args.clean_kwargs(**kwargs)
    kwargs.pop('ignore_epoch', None)
    if kwargs:
        salt.utils.args.invalid_kwargs(kwargs)

    regex = r'^~?([^:\[]+):?[^\[]*\[?.*$'
    ver1 = re.match(regex, pkg1)
    ver2 = re.match(regex, pkg2)

    if ver1 and ver2:
        return portage.versions.vercmp(ver1.group(1), ver2.group(1))
    return None