Get url parameter in Oracle using owa_util

at_get_env_parameter-snipped.sql

/**
* Get parameter from the URL HTTP query string
*
* @param p_attribute Specifies the name of the variable in the HTTP query string to retrieve
* @return value
*/
function at_get_env_parameter (p_attribute in varchar2) return varchar2  as
    p_regex varchar2(254) := '=([^&]*)';
    p_result varchar2(254);
    l_query_strings varchar2(254):= owa_util.get_cgi_env('QUERY_STRING');
begin
    if p_attribute is not null then
        p_result := regexp_substr(l_query_strings, p_attribute || p_regex);
        p_result := substr(p_result, instr(p_result, '=') + 1);
    end if;
    return p_result;
end at_get_env_parameter;