The Annoyance Filter.pdf - Fourmilab

§4 ANNOYANCE-FILTER OPTIONS 5
4. Options.
Options are specified on the command line. Options are treated as commands—most instruct the program
to perform some specific action; consequently, the order in which they are specified is significant; they are
processed left to right. Long options beginning with “−−” may be abbreviated to any unambiguous prefix;
single-letter options introduced by a single “−” without arguments may be aggregated.
−−annotate options
Add the annotations requested by the characters in options to the transcript generated by
the −−transcript option. Upper and lower case options are treated identically. Available
annotations are:
d Decoder diagnostics
p Parser warnings and error messages
w Most significant words and their probabilities
−−autoprune n
−−biasmail n
−−binword n
As the dictionary is bring built by appending mail to it with the −−mail and −−junk
options, unique words will automatically be pruned from it whenever the dictionary
exceeds approximately n bytes. This is particularly handy when loading large collections
of messages with −−phrasemax set greater than one, as a very large number of unique
phrases may clutter the dictionary being built and exceed the memory capacity of your
computer. You could split the mail collection into multiple parts and explicitly −−prune
after each part, but −−autoprune is much more convenient.
The frequency of words appearing in legitimate mail is inflated by the floating point
factor n, which defaults to 2. This biases the classification of messages in favour of
“false negatives”—junk mail deemed legitimate, while reducing the probability of “false
positives” (legitimate mail erroneously classified as junk, which is bad). The higher the
setting of −−biasmail, the greater the bias in favour of false negatives will be.
Binary character streams (for example, attachments of application-specific files, including
the executable code of worm and virus attachments) are scanned and contiguous sequences
of alphanumeric ASCII characters n characters or longer are added to the list of words
in the message. The dollar sign (“$”) is considered an alphanumeric character for these
purposes, and words may have embedded hyphens and apostrophes, but may not begin or
end with those characters. If −−binword is set to zero, scanning of binary attachments is
disabled entirely. The default setting is 5 characters.
−−bsdfolder
The next −−mail or −−junk folder will be parsed using “classic BSD” rules for identifying
the start of individual messages in the folder. In BSD-style folders, the text “From␣” as the
leftmost characters of a line always denotes the start of a new message: any appearance of
this text in any other context is always quoted, often by prefixing a “>” character. In the
default UNIX folder syntax, “From␣” only marks the start of a new message if it appears
following one or more blank lines. Note that you must specify −−bsdfolder before each
folder to be read with BSD rules; it is not a modal setting.
−−classify fname
Classify mail in fname. If it equals or exceeds the junk threshold (see −−threshjunk),
“JUNK” is written to standard output and the program exits with status code 3. If the
message scores less than or equal to the mail threshold (see −−threshmail), “MAIL” is
written to standard output and the program exits with status 0. If the message’s score
falls between the two thresholds, its content is deemed indeterminate; “INDT” is written
to standard output and the program exits with a status of 4. The output can be used
to set an environment variable in Procmail to control the disposition of the message. If
fname is “−” the message is read from standard input.