R_API char *r_sys_cmd_strf(const char *fmt, ...) {
	char *ret, cmd[4096];
	va_list ap;
	va_start (ap, fmt);
	vsnprintf (cmd, sizeof (cmd), fmt, ap);
	ret = r_sys_cmd_str (cmd, NULL, NULL);
	va_end (ap);
	return ret;
}