I have a couple daily taskpaper lists that by the end of the have an @done on each line and I need to reset it for the next day. Instead of trying to do a search and replace everyday, I added a bash alias to .bash_profile (or .bashrc):
alias rst="sed -i '' 's/@done\(.*\)//g'"
The extra '' after the -i is because OS X’s sed requires an extension for backups. Set it to nothing and OS X won’t create backups.