An interesting commandline calender. If you don't supply an argument it will show you the output of cal (current month) but if you supply it a number 12 and lower it will show you that month in this year but if the number is 13 or above it will show you a calender of the year specified.

#!/bin/bash
# Syntax acal 

function acal {
 m=""
 case $# in
    0) cal; return;;                #no arguments
    1) m=$1; y=`date +%Y`;;         #1 argument
    2) m=$1; y=$2;;                 #2 arguments
 esac

 case $m in
      Jan*|jan*      ) m=1;;
      Feb*|feb*      ) m=2;;
      Mar*|mar*      ) m=3;;
      Apr*|apr*      ) m=4;;
      May|may        ) m=5;;
      Jun*|jun*      ) m=6;;
      Jul*|jul*      ) m=7;;
      Aug*|aug*      ) m=8;;
      Sep*|sep*      ) m=9;;
      Oct*|oct*      ) m=10;;
      Nov*|nov*      ) m=11;;
      Dec*|dec*      ) m=12;;
      [1-9]|1[0-2] ) ;;         #numeric month
      *     ) y=$m; m="";;
 esac
 cal $m $y
}

acal $1