Mysqltest hex() not working for string values

  While testing HEX() for string values, getting error seen in below example.  

let $hx1 = $(hex("abc"));

-- echo hex("abc") -> $hx1;             # 616263

MariaDB [(none)]> select hex("abc");

+------------+

| hex("abc") |

+------------+

| 616263     |

+------------+

1 row in set (0.001 sec)