procmailsc man page on OSF1

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       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  con‐
       dition (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  sub‐
	       sequent 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 con‐
       tribute to the score, but simply has to be satisfied.  The other condi‐
       tions  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 maxi‐
       mum  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

	      :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 sur‐
       vived 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	 proc‐
       mail 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 ac‐

       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

BuGless				  2001/08/04			 PROCMAILSC(5)
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