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This is the command filter that can be run in the OnWorks free hosting provider using one of our multiple free online workstations such as Ubuntu Online, Fedora Online, Windows online emulator or MAC OS online emulator



filter - filter incoming messages before adding to mailbox


filter [-q] [-v] [-l] [-o output] [-f rules-file] [-m mailbox]
filter [-n] [-f rules-file]
filter [-r] [-o output] [-f rules-file]
filter [-c] [-s] [-o output] [-f rules-file]
filter [-c] [-S] [-o output] [-f rules-file]


In brief, filter is designed to sort incoming mail based on user preferences for various
recognized headers. It logs a summary of messages filtered to a logfile. See the USAGE
section for full details.


The flags the filter program understands are;

-c Clear logs. If this flag is used, the log files will be removed after being
summarized by either "-s" or "-S" (see below).

-f rules-file
Get rules from specified file instead of default $HOME/.filter/filter-rules

-l Log actions only. Do not log information about mailed messages.

-n Not really. Output what would happen if given message from standard input, but
don't actually do anything with it.

-o file Redirect stdout messages to the specified file or device. Logging of filter
actions is not affected. (This is added to more gracefully deal with changes in
the file system (since sendmail is quite picky about modes of files being
redirected into.))

-m mailbox
Override the compiled in definition of your primary 'mailbox'. This is disabled
if filter is setgid.

-q Quiet. Do not log filtering actions.

-r Rules. List the rules currently being used.

-s Summarize. List a summary of the message filtering log.

-S This is the same as `-s' but includes message-by-message information

-v Verbose. Give output on standard out for each message filtered. May be useful
to set output to ``/dev/console'' or other logging device. (see -o).


Filter uses a set of selection rules to process incoming mail messages. These rules are
normally read in from $HOME/.filter/filter-rules. As soon as a rule matches something
about the message, that rule is used, and no further action is taken. The general format
for a rule is;

if (expression) then action

where expression is:

expression ::= { not } condition { and expression }

condition ::= field = stringvalue
::= field != stringvalue
::= lines relop numvalue
or ::= always

These further break down as:

field ::= from | subject | alphasubject | to | lines | sender

relop ::= = | != | < | > | <= | >=

stringvalue ::= any quoted string

numvalue ::= any integer value

Note: alphasubject is a transformed version of the subject line, where only alpha chars
are preserved, and they are forced to lower case. It is then simpler to use a regular
expression match across a wide variety of similar subjects.

from matches any and all of the following headers:
"From " From: Reply-To: Sender:

Action can be any of:

delete (ignore this message; throw it away)
save foldername (put in 'foldername' for later)
savecopy foldername (save a copy AND put in my inbox)
execute command (pipe message to 'command')
executec command (copy to inbox, AND pipe to 'command')
forward address (forward this message)
forwardc address (forward this message, AND copy to inbox)
resend address (resend to new addr without change)
leave (just put it in my inbox)
bounce (say there's no such user)

An example of a rules file would be:

# I'll read this stuff later when I feel like it
if (from = "[email protected]") then save "~/Mail/mailinglist"
# This mailing list actually has an x-mailing-list header
if (mailinglist = "[email protected]") then save "~/Mail/otherlist"
# auto-archive this project's email, AND put in my current mailbox
if (subject = "strange project") then savecopy "~/Mail/proj-archive"
# If "make money" appears ANYWHERE in subject, upper/lowercase,
# delete the lousy spam
if ( subject = "make money" ) then delete
# This person no longer shares this virtual mailbox with me.
# Resend visibly as a "forwarded" message.
if (to = "partner") then forward "[email protected]"
# If email for an old address comes to me, resend to new one.
# Note that the "envelope" will show my address, but the
# normal headers will not
if ( to = "old_address" ) then resend [email protected]"
# Special virtual headerline derived from normal subject line
# catches "multiple!!!wor+ds**here"
if ( alphasubject = "multiplewordshere" ) then delete
# If email for a special address comes to me, resend through
# a non-standard "special" mailer
if ( to = "special_address" ) then exec "/usr/lib/mailer special@addr"
# The rules file doesn't really need parentheses. Or even the 'if'.
# They are just traditional.
subject = "silly" then bounce

Note that all filenames must be double-quoted

For further information about the rules language, please see The Elm Filter Guide.


Philip Brown

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