#!/bin/sh
# ymd2yd converts yyyymmdd to yyyyddd
# usage ymd2yd 19980429

# if there is no command line argument, then assume that the date
# is coming in on a pipe and use read to collect it

if [ $# = 0 ]
then
read dt
else
dt=$1
fi

# break the yyyymmdd into separate parts for year, month and day

y=`expr $dt / 10000`
m=`expr \( $dt % 10000 \) / 100`
d=`expr $dt % 100`

# add the days in each month up to (but not including the month itself)
# into the days. For example if the date is 19980203 then extract the
# number of days in January and add it to 03. If the date is June 14, 1998
# then extract the number of days in January, February, March, April and May
# and add them to 14.

x=1
while [ `expr $x \< $m` = 1 ]
do
md=`monthdays $y $x`
d=`expr $d + $md`
x=`expr $x \+ 1`
done

# combine the year and day back together again and you have the julian date.

jul=`expr \( $y \* 1000 \) + $d`
echo $jul