Get last day of last month (ksh )

Get last day of last month (ksh )

# get current month
month=$(expr `date +%m` - 1 )
# get current year 
year=`date +%Y`
# last day
day=`cal $month $year | grep -v "^$" | tail -1 | awk '{print $NF}'`

eg

cal 2 2008 | grep -v "^$" | tail -1 | awk '{print $NF}'
29