Calendar in linux shell programming problems

Question

I want my calendar to correctly handle months with leading zeros for example: "cal 01" or "cal 01 2012"

How do I write the code to make my calendar to correctly handle months with leading zeros?

This is my code so far:

$ cat cal
#cal: nicer interface to /usr/bin/cal

case $# in
0)  set 'data';m=$2; y=$6 ;;    # no argu: use today
1)  m=$1; set 'data'; y=$6 ;;   # 1 rg: use this year
*)  m=$1; y=$2 ;;           # 2 ags: month and year 
esac

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

/usr/bin/cal $m $y          # run the real one
$

Answer 1

You can do multiple regex matching in your case statement, i.e.

case $m in
01|1|jan*|Jan*)  m=1 ;;
02|2|feb*|Feb*)  m=2 ;;

....

Else, you could use shell parameter substitution to remove any leading 0's, i.e.

# as a way to demonstrate param sub on $1 etc, load values to $1 and $2
set -- 01 02 
echo ${1#0}
echo ${2#0}

# output
1
2

Edit

For your follow-up question

Example, the current month is November, 2005, if you run "cal 01", you should print out the calendar of Jan. 2006

Try this:

# if the month input is less than the current month, assume the next year
if (( ${y:-0} == 0  && m < $(/bin/date +%m) )) ; then
   y=$(/bin/date +%Y)
   ((y++))
fi

${y:-0} is one of several parameter checking syntaxs provided by most shells that allows a default value to be substituted if the var value is completely unset (not set at all) or = "". So in this case, if y wasn't set by the command line, it will appear as 0 in this evaluation, allowing the && section to be be executed to test the month, etc.

You'll need to extend your case $# processing to allow for 1 argument, that is assumed to be a month value.

I hope this helps.