A Challenge to Rick: a really weird .forward file.

[Rick Stevens]

Waldher, Travis R wrote:
> Here's the deal... I have a .forward file as follows:
> 
> "|IFS=' '&&p=/usr/bin/procmail&&test -f $p&&exec $p -Yf-||exit 75
> #username"
> 
> The catch is, this causes sendmail 8.12 to not work (bounces email back
> as undeliverable), but is required by postfix on other systems to let
> procmail do it's job.
> 
> Meaning, I have to have that line (or some form of it) but on the other
> hand, I can't either.  Bad catch 22.
> 
> My biggest problem, I have NO idea what that line is doing and neither
> does anyone I work with.
> 
> Also, can I add an algorithm so that when it's called, can it do nothing
> if it's a sendmail based system, and execute that line if it's postfix?
> 
> Thanks in advance

What do I get if I figure it out?  Do I get a pony? Do I?  Do I? :-)

Just break it down, Travis.  The "&&" is a standard shell convention for
"if this is true, do A, AND if A is true, do B, AND if B is true...".
In other words, the next part of the pipe (reading left to right) is
executed ONLY if the previous part returned a "true" (return value of
0).  Conversely, "||" means "OR": "if A fails, do B"

So, the first bit sets the input field separator (IFS) to a space (see
"Shell Variables" in "man bash").

If that was successful (and it will be), it sets "p" to the value
"/usr/bin/procmail".  This is simply so the script doesn't have 
"/usr/bin/procmail" all over the place.

If that was successful (again, it should be), then it checks to see if
"/usr/bin/procmail" is a regular file.  I think that's bad.  It should
be "test -x $p", or "if /usr/bin/procmail is executable".

If it is a regular file (or executable with my change), then execute it
and pass it the arguments "-Yf-" (methinks that should be "-Yf -").
"-Y" to procmail says "assume traditional mailbox format", the "-f -"
(note the space between "f" and the second dash) means "update the
timestamp of the "From " line, if any.

The || means "if any of the preceeding stuff fails, exit with a value of
75" (which is "EX_TEMPFAIL" from /usr/include/sysexits.h).  Sendmail 
expects any delivery agent (e.g. procmail) to return a value from
/usr/include/sysexits.h.

The "#username" bit I'm a bit confused on, but I think it's supposed to
be "$username" (the username the message is meant for).

In pseudo-code:

     If setting the input field separator to a space is OK, AND
	If setting "p" to /usr/bin/procmail is OK, AND
	    If "/usr/bin/procmail" is a file (executable), THEN
		execute "/usr/bin/procmail -Yf - $username"
		return whatever procmail generates for a result code
	    Else
		exit with EX_TEMPFAIL (75)
	    Fi
	Else
	    exit with EX_TEMPFAIL (75)
	Fi
     Else
	exit with EX_TEMPFAIL (75)
     Fi

Does that make sense to you?  Do I get the pony?
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- Rick Stevens, Senior Systems Engineer     rstevens at vitalstream.com -
- VitalStream, Inc.                       http://www.vitalstream.com -
-                                                                    -
-  The problem with being poor is that it takes up all of your time  -
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