bogofilter script

[Michael Gale]

Hello,

	I have been using Bogofilter for some time now and it works great, but 
I am now curious on how the bogofilter script works, if some one could 
explain the following or correct me understanding that would be great.

Script from bogofilter documentation:


	#!/bin/sh

         FILTER=/usr/bin/bogofilter
         FILTER_DIR=/var/spool/filter
         POSTFIX=/usr/sbin/sendmail
         export BOGOFILTER_DIR=/home/bogofilter

         # Exit codes from <sysexits.h>
         EX_TEMPFAIL=75
         EX_UNAVAILABLE=69

         cd $FILTER_DIR || \
             { echo $FILTER_DIR does not exist; exit $EX_TEMPFAIL; }

         # Clean up when done or when aborting.
         trap "rm -f msg.$$ ; exit $EX_TEMPFAIL" 0 1 2 3 15

         # bogofilter -e returns: 0 for OK, nonzero for error
         rm -f msg.$$ || exit $EX_TEMPFAIL
         $FILTER -p -u -e > msg.$$ || exit $EX_TEMPFAIL

         exec <msg.$$ || exit $EX_TEMPFAIL
         rm -f msg.$$ # safe, we hold the file descriptor
         exec $POSTFIX "$@"
         exit $EX_TEMPFAIL


The first part is easy:
         FILTER=/usr/bin/bogofilter
         FILTER_DIR=/var/spool/filter
         POSTFIX=/usr/sbin/sendmail
         export BOGOFILTER_DIR=/home/bogofilter

Set up the variables and export the BOGOFILTER_DIR variable.

The second part is also easy:
         # Exit codes from <sysexits.h>
         EX_TEMPFAIL=75
         EX_UNAVAILABLE=69

         cd $FILTER_DIR || \
             { echo $FILTER_DIR does not exist; exit $EX_TEMPFAIL; }

         # Clean up when done or when aborting.
         trap "rm -f msg.$$ ; exit $EX_TEMPFAIL" 0 1 2 3 15

Set two exit codes, a FILTER_DIR check and a trap for signals 0,1,2,3,15


This is where I get a little confused:

         # bogofilter -e returns: 0 for OK, nonzero for error
         1. rm -f msg.$$ || exit $EX_TEMPFAIL
         2. $FILTER -p -u -e > msg.$$ || exit $EX_TEMPFAIL

         3. exec <msg.$$ || exit $EX_TEMPFAIL
         4. rm -f msg.$$ # safe, we hold the file descriptor
         5. exec $POSTFIX "$@"
         6. exit $EX_TEMPFAIL

line 2. Has bogofilter read from input / pipe a message and direct the 
out put to msg.$$ (process ID) and exit if unable to do so.

line 3. Passes the new file containing the scanned message to the exec 
function ?

line 4. Removes the message

line 5. Executes sendmail passing the argument array $@
  that contains the new message.

line 6. Exit with a EX_TEMPFAIL ?


I don't understand line 1. < Why the need to remove a file that should 
not exist ? Also if EX_TEMPFAIL is a exit status when some thing goes 
wrong why does it exit with that value at the end ?

Thanks.






-- 
Michael Gale
Lan Administrator
Utilitran Corp.

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