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PROCMAILSC(5)                                                                                  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 ------k=1
                  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  num-ber number
               ber of matches found.

       0<x<1   Every  match  will contribute less to the score than the previous one.  The score will asymp-
               totically 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 vir-
       tual number of matches.  Calculation of the added score then proceeds as if it had been a normal reg-ular regular
       ular 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 condi-tion condition
       tion 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 prior-ity priority
       ity 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 appreci-ated appreciated
       ated (the score for those will reach a maximum of 3500), those three people usually don't send inter-esting interesting
       esting 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 con-tains contains
       tains 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  fol-lowing following
       lowing  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 abso-lutely absolutely
       lutely  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  sur-vived survived
       vived 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 -------ln
                     ln x

       matches.

AUTHORS
       Stephen R. van den Berg
              <srb@cuci.nl>
       Philip A. Guenther
              <guenther@sendmail.com>



BuGless                                          2001/08/04                                    PROCMAILSC(5)