procmailsc - procmail weighted scoring technique


   [*] w^x condition


   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

   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:
   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   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

   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:

              /  M  \
          w * | --- |
              \  L  /


          * w^x  < L

   will generate an additional score of:

              /  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.


   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).


   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  ^.*$

   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

   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.

          ^From mailinglist-request@some.where
            * ^(From:.*(paula|bill)|Subject:.*skiing)

            :0 Bh
            *  20^1 ^>
            * -10^1 ^[^>]


   For further examples you should look in the procmailex(5) man page.


   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).


   procmail(1), procmailrc(5), procmailex(5), sh(1), csh(1), egrep(1),


   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

   Floating  point  numbers  in  `engineering' format (e.g., 12e5) are not


   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.


   If in a regular expression weighted  formula  0<x<1,  the  total  added
   score for this condition will asymptotically approach:

           1 - x

   In order to reach half the maximum value you need

               - ln 2
          n = --------
                 ln x



   Stephen R. van den Berg
   Philip A. Guenther


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