I use this to set the subject of an email that notifies my team of a Capistrano deploy. The part of interest is how it gets the subversion revision number with a few piped shell commands.
echo "Subject: [rake deploy] Deployed revision `cd /home/www/current ; svn info | grep Revision | sed "s/Revision: //"` on `hostname` at `date`" > ~/sendmail_tmp
