#write out current crontab to a temporary file “mycron”
crontab -l > mycron

#echo new cron task into the temporary file
echo “0 5 * * * /bin/find /tmp -type f -iname ‘sess_*’ -mtime +7 -exec rm -rf {} \;” >> mycron

#and finally, install new cron file
crontab mycron
rm mycron