Ammending Date-Time Stamps to a file

Hiya,
I would like to date time stamp ammendments to a file.
The problem is getting the time stamp into the variable DATE.
As the logfile shows, `date' is executed, and then ? goes looking for 
some sort of file etc.
Thanks in advance for your thoughts.
Shane

DATE=`date +%y%m%d%H%M`

:0H:
*^FROM:.*857
| echo "857 $DATE >> /home/857.txt

Logfile
procmail: Executing "date,+%y%m%d%H%M"
date: date: No such file or directory
procmail: Assigning "DATE="

Output file 857.txt
857 etc but no date time stamp 
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