Provided by: procmail_3.22-16ubuntu5_i386 bug

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>