$ perl -Mstrict -Mwarnings -le '
    sub fun { print "@_" }
    #fun(1, url);
    fun(2, -url);
    fun(3, -url, "httpRefer");
    fun(4, -url => "httpRefer");
    #fun(5, url, "httpRefer");
    fun(6, url => "httpRefer");
'
2 -url
3 -url httpRefer
4 -url httpRefer
6 url httpRefer