Gnus' nnmaildir has a neat feature where it can watch a directory of
symlinks representing its monitored folders, and automatically add
symlinks when it creates a folder. However, since I tend to create
folders in Mutt or procmail rather than Gnus, I need a script that'll
watch my collection of folders and add new symlinks periodically. (It
should also use a .nnmaildir-not directory for symlinks to
folders that it knows shouldn't be watched; I can then just move
symlinks between the two by hand to control what should and shouldn't be
presented to nnmaildir.
Implemented as update-nnmaildir.