i made some syntax modification which are:

#old=1/1/07
old=`date +%d%m%y`
var="(`(date -u $old "+%s")`/ 86400)"
echo $var

but i have a problme with the third line..

when i read man page for date, it only supports

usage: date [-u] mmddHHMM[[cc]yy][.SS]
date [-u] [+format]
date -a [-]sss[.fff]

i'm guessing i should use -u but i think it's wrong