procmailsc(5)
NAME
procmailsc - procmail weighted scoring technique
SYNOPSIS
[*] w^x condition
DESCRIPTION
In addition to the traditional true or false conditions you can specify
on a recipe, you can use a weighted scoring technique to decide if a
certain recipe matches or not. When weighted scoring is used in a
recipe, then the final score for that recipe must be positive for it to
match.
A certain condition can contribute to the score if you allocate it a
`weight' (w) and an `exponent' (x). You do this by preceding the
condition (on the same line) with:
w^x
Whereas both w and x are real numbers between -2147483647.0 and
2147483647.0 inclusive.
Weighted regular expression conditions
The first time the regular expression is found, it will add w to the
score. The second time it is found, w*x will be added. The third time
it is found, w*x*x will be added. The fourth time w*x*x*x will be
added. And so forth.
This can be described by the following concise formula:
n
n k-1 x - 1
w * Sum x = w * -------
k=1 x - 1
It represents the total added score for this condition if n matches are
found.
Note that the following case distinctions can be made:
x=0 Only the first match will contribute w to the score. Any
subsequent matches are ignored.
x=1 Every match will contribute the same w to the score. The score
grows linearly with the number of matches found.
0<x<1 Every match will contribute less to the score than the previous
one. The score will asymptotically approach a certain value
(see the NOTES section below).
1<x Every match will contribute more to the score than the previous
one. The score will grow exponentially.
x<0 Can be utilised to favour odd or even number of matches.
If the regular expression is negated (i.e., matches if it isn't found),
then n obviously can either be zero or one.
Weighted program conditions
If the program returns an exitcode of EXIT_SUCCESS (=0), then the total added score will be w. If it returns any other exitcode (indicating failure), the total added score will be x. If the exitcode of the program is negated, then, the exitcode will be considered as if it were a virtual number of matches. Calculation of the added score then proceeds as if it had been a normal regular expression with n=`exitcode' matches.
Weighted length conditions
If the length of the actual mail is M then:
* w^x > L
will generate an additional score of:
x
/ M \
w * | --- |
\ L /
And:
* w^x < L
will generate an additional score of:
x
/ L \
w * | --- |
\ M /
In both cases, if L=M, this will add w to the score. In the former
case however, larger mails will be favoured, in the latter case,
smaller mails will be favoured. Although x can be varied to fine-tune
the steepness of the function, typical usage sets x=1.
MISCELLANEOUS
You can query the final score of all the conditions on a recipe from the environment variable $=. This variable is set every time just after procmail has parsed all conditions on a recipe (even if the recipe is not being executed).
EXAMPLES
The following recipe will ditch all mails having more than 150 lines in
the body. The first condition contains an empty regular expression
which, because it always matches, is used to give our score a negative
offset. The second condition then matches every line in the mail, and
consumes up the previous negative offset we gave (one point per line).
In the end, the score will only be positive if the mail contained more
than 150 lines.
:0 Bh
* -150^0
* 1^1 ^.*$
/dev/null
Suppose you have a priority folder which you always read first. The
next recipe picks out the priority mail and files them in this special
folder. The first condition is a regular one, i.e., it doesn't
contribute to the score, but simply has to be satisfied. The other
conditions describe things like: john and claire usually have something
important to say, meetings are usually important, replies are favoured
a bit, mails about Elvis (this is merely an example :-) are favoured
(the more he is mentioned, the more the mail is favoured, but the
maximum extra score due to Elvis will be 4000, no matter how often he
is mentioned), lots of quoted lines are disliked, smileys are
appreciated (the score for those will reach a maximum of 3500), those
three people usually don't send interesting mails, the mails should
preferably be small (e.g., 2000 bytes long mails will score -100, 4000
bytes long mails do -800). As you see, if some of the uninteresting
people send mail, then the mail still has a chance of landing in the
priority folder, e.g., if it is about a meeting, or if it contains at
least two smileys.
:0 HB
* !^Precedence:.*(junk|bulk)
* 2000^0 ^From:.*(john@home|claire@work)
* 2000^0 ^Subject:.*meeting
* 300^0 ^Subject:.*Re:
* 1000^.75 elvis|presley
* -100^1 ^>
* 350^.9 :-\)
* -500^0 ^From:.*(boss|jane|henry)@work
* -100^3 > 2000
priority_folder
If you are subscribed to a mailinglist, and just would like to read the
quality mails, then the following recipes could do the trick. First we
make sure that the mail is coming from the mailinglist. Then we check
if it is from certain persons of whom we value the opinion, or about a
subject we absolutely want to know everything about. If it is, file
it. Otherwise, check if the ratio of quoted lines to original lines is
at most 1:2. If it exceeds that, ditch the mail. Everything that
survived the previous test, is filed.
:0
^From mailinglist-request@some.where
{
:0:
* ^(From:.*(paula|bill)|Subject:.*skiing)
mailinglist
:0 Bh
* 20^1 ^>
* -10^1 ^[^>]
/dev/null
:0:
mailinglist
}
For further examples you should look in the procmailex(5) man page.
CAVEATS
Because this speeds up the search by an order of magnitude, the procmail internal egrep will always search for the leftmost shortest match, unless it is determining what to assign to MATCH, in which case it searches the leftmost longest match. E.g. for the leftmost shortest match, by itself, the regular expression: .* will always match a zero length string at the same spot. .+ will always match one character (except newlines of course).
SEE ALSO
procmail(1), procmailrc(5), procmailex(5), sh(1), csh(1), egrep(1), grep(1),
BUGS
If, in a length condition, you specify an x that causes an overflow, procmail is at the mercy of the pow(3) function in your mathematical library. Floating point numbers in `engineering' format (e.g., 12e5) are not accepted.
MISCELLANEOUS
As soon as `plus infinity' (2147483647) is reached, any subsequent weighted conditions will simply be skipped. As soon as `minus infinity' (-2147483647) is reached, the condition will be considered as `no match' and the recipe will terminate early.
NOTES
If in a regular expression weighted formula 0<x<1, the total added
score for this condition will asymptotically approach:
w
-------
1 - x
In order to reach half the maximum value you need
- ln 2
n = --------
ln x
matches.
AUTHORS
Stephen R. van den Berg
<srb@cuci.nl>
Philip A. Guenther
<guenther@sendmail.com>
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