#!/bin/bash
# http://redsymbol.net/articles/unofficial-bash-strict-mode/
# mydate: convert 'oct 24' to '10 2024' for the cal command
# Actually, modern versions of cal do accept the month as "jan" or "january", etc.
# Try the month 9 1752

DEBUG=1

set -eu
set -o pipefail

if [ $# -ne 2 ]
then
	echo "usage: mycal month year"
	exit 1
fi

MONTH=$1
YEAR=$2

if test $YEAR -lt 100    	# two-digit year
then
    YEAR=$(($YEAR + 2000))
fi

MONTH=$(echo $MONTH | tr '[A-Z]' '[a-z]')	# convert to lowercase; escape char classes from shell
if test $DEBUG -eq 1;then echo "MONTH is $MONTH"; fi

if [[ $MONTH =~ ^[a-z] ]]	# if MONTH starts with a letter; this is a regular expression
then
case $MONTH in 
    january|jan)
        MONTH=01;;        
    february|feb)
        MONTH=02;;
    march|mar)
        MONTH=03;; 
    april|apr)
        MONTH=04;;
    may)
        MONTH=05;;
    june|jun)
        MONTH=06;;
    july|jul)
        MONTH=07;;
    august|aug)
        MONTH=08;;
    september|sep|sept)
        MONTH=09;;
    october|oct)
        MONTH=10;;
    november|nov)
        MONTH=11;;
    december|dec)
        MONTH=12;;        
    *)			# this is a pattern match; "*" matches everything
        echo "$MONTH is not a month"
        exit 1;;
esac
fi

if test $DEBUG -eq 1;then echo "MONTH is $MONTH, YEAR is $YEAR"; fi
 
cal $MONTH $YEAR