Shell Programming and Scripting

I've never tested file length with shell before and I'm having problems. What I'm doing is testing $filename and $filename.bak to see if there is a difference. so I use 'diff' for that and send it to an output file 'dif.txt'. Now I wanna see if the length of 'dif.txt' is zero or not. that's where i'm stuck. Here's what i gotusing /csh)

diff ${filename} ${filename}.bak > dif.txt
if ( test -z dif.txt )
echo "New Backup Not Needed"
else
cp ${filename} "${filename}.bak<DATE>"
echo "New Backup Created"
endif

Also, I need assistance with proper input of todays DATE.
THANKS

Here is something which should work for you. You were not very clear on what you wanted to do with DATE so I just appended it to .bak

Code:

#!/usr/bin/csh

set filename=myfile
set date=`date +%Y%m%d`

diff ${filename} ${filename}.bak > dif.txt
if ( -z dif.txt ) then
   echo "New backup not needed"
else
   cp ${filename} "${filename}.bak.${date}"
   echo "New backup created on $date"
endif