ENV.rassoc

static VALUE
env_rassoc(VALUE dmy, VALUE obj)
{
    obj = rb_check_string_type(obj);
    if (NIL_P(obj)) return Qnil;

    VALUE result = Qnil;

    ENV_LOCK();
    {
        char **env = GET_ENVIRON(environ);

        while (*env) {
            const char *p = *env;
            char *s = strchr(p, '=');
            if (s++) {
                long len = strlen(s);
                if (RSTRING_LEN(obj) == len && strncmp(s, RSTRING_PTR(obj), len) == 0) {
                    result = rb_assoc_new(rb_str_new(p, s-p-1), obj);
                    break;
                }
            }
            env++;
        }
        FREE_ENVIRON(environ);
    }
    ENV_UNLOCK();

    return result;
}