I am trying to subtract an integer from a date. Basically I am trying to say that if it is the before the 15th of the month, so subtract 1 from the month. So if the day is 05-05-2016 I want to use 04 as the month.
If [ $Day -lt 15 ]
Output_Month=$Month - 1
The date command is quite smart, you can just write:
if [ $Day -lt 15 ]; then Output_Month=$(date -d "-1 month" +%m) fi