procmail save into a dir and execute a script?

Question

I'm using procmail with Maildir/ and easy rules like the one below to save incoming emails into directories:

:0:
* ^X-Spam-Status: Yes
Spam/

Now I would like a desktop notification on new emails in certain directories/rules, I know already how to handle notifications but how to tell procmail to save into a directory and execute a script?

I know I can pipe a |command but I would prefer to let procmail saving the file, then just run a script.

Having the email (headers at least) in pipe or the dir+file path as arguments would be nice, run the script asynchronous would also be nice.

update

So, based on @slm's answer that's the result:

:0 c:
* ^X-Spam-Status: Yes
Spam/

:0 Whi
* ^X-Spam-Status: Yes
| $HOME/install/bin/notify.sh

c copy the message in the directory but goes on with next rules

I'm not using f becase that's not a filter, if the rule match I want procmail to stop here (I hope I'm not misunderstanding the manual here)

W to suppress any program failure

h to pipe only headers

i to ignore any write error to the pipe

I'm not using w because don't want to wait the script to return

I think I don't need a lock file too (no : after Whi)

update 12/5/14

In the end I've adopted exactly the solution @tripleee proposed.

Played around also with mailutils-comsatd for few minutes before give up.

.procmailrc:

COMSAT=no

Answer 1

To run the mail through a script you can modify your rule like so using 2 rules:

:0: c
* ^X-Spam-Status: Yes
Spam/

:0: fw
* ^X-Spam-Status: Yes
| /usr/bin/python /work/scripts/process_mail.bash

Your program will receive the mail on STDIN. You'll have to 'echo' the possibly transformed mail on STDOUT.

fw means:

• f Consider the pipe as a filter.
• w Wait for the filter or program to finish and check its exitcode (normally ignored); if the filter is unsuccessful, then the text will not have been filtered.
• c Generate a carbon copy of this mail. This only makes sense on delivering recipes. The only non-delivering recipe this flag has an effect on is on a nesting block, in order to generate a carbon copy this will clone the running procmail process (lockfiles will not be inherited), whereby the clone will proceed as usual and the parent will jump across the block.

References

• Want procmail to run a custom python script, everytime a new mail shows up

Answer 2

Here's a slight adaptation of @slm's answer.

You should not use locking with Maildir, and the flags and the lock colon were the wrong way around. (You would effectively create a lock file named c, rather than clone the message, so the second action would never fire.)

The f flag seems out of place.

I reversed the order of the actions; while it makes sense to deliver, then notify, from the point of view of Procmail, the notification is a secondary action which is allowed to fail, so I do that in a clone and ignore its exit status.

Finally, grouping two actions under one condition is more intuitive using braces.

:0
* ^X-Spam-Status: Yes
{
    :0cWhi
    | $HOME/install/bin/notify.sh
    :0
    Spam/
}

Having said that, I also note that Procmail already generates comsat notifications out of the box. That's a legacy notification protocol, but you might be able to use it for something. Secondly, a simple notification mechanism could be built using a script which monitors your procmail.log instead. (But yeah, parsing log files sucks.)