procmailsc

NAME

       procmailsc - procmail weighted scoring techique

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  scor-
       ing  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.

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 exponen-
               tionally.

       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 exit-
       code  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=`exit-
       code' 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 func-
       tion, 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  condi-
       tions  on  a  recipe (even if the recipe is not being exe-
       cuted).

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  con-
       sumes  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  some-
       thing  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 men-
       tioned, 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,  smi-
       leys  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 uninter-
       esting 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 previ-
       ous 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  magni-
       tude,  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 to-
       tal added score for this condition will asymptotically ap-
       proach:

                 w
              -------
               1 - x

       In order to reach half the maximum value you need

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

       matches.

AUTHOR

       Stephen R. van den Berg at RWTH-Aachen, Germany
              berg@pool.informatik.rwth-aachen.de