I have a set of maildirs (one for each mailing list / other context) and want to know which of them contains unread mail without firing up my MUA.
Luckily, this is easy to do on the commandline without even looking at mail contents, as there's (mostly?) two kinds of unread mail:
- new and unprocessed mail. These messages are stored in
Maildir/new, so if there's anything in there, it's an unread mail
- new but no longer "Recent" mail. These messages have not been read yet, but
have already been transferred to a MUA using a Read-Write operation, causing
them to be marked as no longer new on the server side. They are stored in
Maildir/curalongside read mail, but do not have the "Seen" (S) flag set.
This is easy to check with zsh globbing:
new/*(N) expands to a non-empty
list if new and unprocessed mail is present, and
cur/*~*,*S*(N) expands to
a non-empty list if old but unread mail is present. Note that it requires
extended_glob zsh option to be set.