Syntactic error in bash case statement

Question

#!/bin/bash

dia=$(date +"%d")
echo $dia
mes=$(date +"%m")

case $mes
01)  $mes='Jan';;
02)  $mes='Feb';;
03)  $mes='Mar';;
04)  $mes='Apr';;
05)  $mes='May';;
06)  $mes='Jun';;
07)  $mes='Jul';;
08)  $mes='Aug';;
09)  $mes='Sep';;
10)  $mes='Oct';;
11)  $mes='Nov';;
12)  $mes='Dec';;
esac

The error is the following

./check_brute_force.sh: line 18: syntactic error near unexpected element `01'

Answer 1

Missing "in" keyword

case $mes in

Answer 2

The case statement needs an in, e.g.:

case $mes in