Ed Wildgoose writes:

Yes it does. At least the maildropfilter page I'm looking at has a section called "PATTERNS", which describes every regular expression syntax implemented by maildrop. If something does not appear in that section, then it's not implemented, as far as regular expressions go.

I'm going to reproduce that portion of the man page, then you can explain to me what exactly "DOESN'T describe exactly what works", below:

PATTERNS The pattern syntax in maildrop is similar to the grep command’s syn- tax, with some minor differences. A pattern takes the following form in the filter file:

/pattern/:options

pattern specifies the text to look for in the message. pattern, because the leading slash will then be interpreted as a division sign. If you must search for text that starts with a space, use something [snip] patterns. For example:

/^From: *!.*/ matched against the same line will set MATCH to "From: " and MATCH2 to "postmaster@localhost". More than one ! character may be used. Sub- sequent matched text is assigned to MATCH3, MATCH4, and so on.

Note: Please note that the abuse of this feature will eat plenty of CPU time -- the ! character introduces a lot of com- plexity for maildrop to deal with.

When there is more than one way to match a string, maildrop favors matching as much as possible initially. For example:

/^To:.*,!.*/ when matched against

To: joe@somewhere,bo...@somewhere.else,gary@whoknowswhere will set MATCH to "To: joe@somewhere,bo...@somewhere.else," and MATCH2 to "gary@whoknowswhere".

The MATCH variables are NOT set when weighted scoring is used, since the same pattern is matched multiple times.

I'm converting some filters from procmail and I use the following construct quite a lot:

if (/^From: *(someaddress@somewhere|someotheraddress|somewhereelse)/) { }

However, it's not documented as being valid syntax in the maildrop documentation. I didn't even think to just try it, but converted a bunch of filters to a repetitive IF syntax instead. Completely by chance I spotted that it was possible from someones example filter.