Validate long date format in If statement

Shell Programming and Scripting
1

Hi,

I want to validate if the given input is a valid month (written in long month format)

Jan / Feb / Mar / Apr / May / Jun etc etc

This is what I've got with || (or statements):

 
#!/usr/bin/ksh
INPUT_DATE=$1
FORMATTED_DATE=`date | cut -f2 -d' '`
#If there's no input use the sysdate otherwise use the input
if [[ -z "$INPUT_DATE" ]] ; then
   MONTH_TO_PROCESS=$FORMATTED_DATE
else
   MONTH_TO_PROCESS=$1
fi
echo $MONTH_TO_PROCESS
 
if [[ "$MONTH_TO_PROCESS" = "Feb" || "$MONTH_TO_PROCESS" = "Jan" || "$MONTH_TO_PROCESS" = "Mar"]]; then
   echo "$MONTH_TO_PROCESS is Valid"
else
   echo "$MONTH_TO_PROCESS is Invalid"
fi

But when I use this for every month (jan - dec), the list is too long and I get an error.

This is what I want (but this is too long), how can i validate the month or cut all the or statements over multiple lines, I tried // but that doesn't work:

if [[ "$MONTH_TO_PROCESS" = "Feb" || "$MONTH_TO_PROCESS" = "Jan" || "$MONTH_TO_PROCESS" = "Mar" || "$MONTH_TO_PROCESS" = "Apr" || "$MONTH_TO_PROCESS" = "May" || "$MONTH_TO_PROCESS" = "Jun" || "$MONTH_TO_PROCESS" = "Jul" || "$MONTH_TO_PROCESS" = "Aug" || "$MONTH_TO_PROCESS" = "Sep" || "$MONTH_TO_PROCESS" = "Oct" || "$MONTH_TO_PROCESS" = "Nov" || "$MONTH_TO_PROCESS" = "Dec"]]; then
2

Solved my problem, with a Case:

case $MONTH_TO_PROCESS in
Jan) echo "Valid" ;;
Feb) echo "Valid" ;;
Mar) echo "Valid" ;;
Apr) echo "Valid" ;;
May) echo "Valid" ;;
Jun) echo "Valid" ;;
Jul) echo "Valid" ;;
Aug) echo "Valid" ;;
Sep) echo "Valid" ;;
Oct) echo "Valid" ;;
Nov) echo "Valid" ;;
Dec) echo "Valid" ;;
*) echo "$MONTH_TO_PROCESS is not a valid month, this should be one of Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec"
exit;;
esac