Listing 3. maildate.sh Script

#!/bin/bash
# maildate.sh - calculate date as integer days 
# since 1900
#          Sample input: "Feb 2 1997"
month=$1 # Received as three-character
	 # abbreviation
day=$2   # Received as integer 1 through 31
year=$3  # Received as integer 1900 through 2099

# Compute days from 1900 to beginning of year 
# excluding leap days
days1900=$[ ( year - 1900 ) * 365 ]

# Compute approximate leap days since 1900 ; if 
# current year is divisible by four and date is
# before 1 Mar then this will overstate leap 
# days by one
leapdays=$[ ( year - 1900 ) / 4 ]

# If current year is a leap year then adjust if 
# before 1 Mar
if [ $[ year % 4 ] -eq 0 ] && \
   ([ $month = "Jan" ] || [ $month = "Feb" ])
then
  leapdays=$[ leapdays - 1]
fi<\n> 

#Compute days into year
case $month in
	'Jan')	daysintoyear=0 ;;
	'Feb')	daysintoyear=31 ;;
	'Mar')	daysintoyear=59 ;;
	'Apr')	daysintoyear=90 ;;
	'May')	daysintoyear=120 ;;
	'Jun')	daysintoyear=151 ;;
	'Jul')	daysintoyear=181 ;;
	'Aug')	daysintoyear=212 ;;
	'Sep')	daysintoyear=243 ;;
	'Oct')	daysintoyear=273 ;;
	'Nov')	daysintoyear=304 ;;
	'Dec')	daysintoyear=334 ;;
esac
dayssince1900=$[ daysintoyear + leapdays + \ 
	days1900 + day ]
echo $dayssince1900