To see that what we describe is actually what happens, take a moment to add rule set 0 to the end of your client.cf file:
S0 # select delivery agent
newR$+ $#hub $@${REMOTE} $:$1 forward to hub
new
Now run sendmail in rule-testing mode and give it
the address boss@acme
:
%./sendmail -Cclient.cf -bt
ADDRESS TEST MODE (ruleset 3 NOT automatically invoked) Enter <ruleset> <address> >0 boss@acme
rewrite: ruleset 0 input: boss @ acme rewrite: ruleset 0 returns: $# hub $@ mailhost $: boss @ acme
The change to the workspace caused by rule set 0 is exactly as predicted:
$# hub $@ mailhost $: boss @ acme
Components from the workspace triple are used by sendmail to define
macros used by delivery agents. For example, the text after $@
is copied into the h
macro. Similarly, the username appearing after
$:
is copied into the u
macro:
from $@ in rule set 0 Mhub, P=[IPC], S=0, R=0, F=mDFMuXa, T=DNS/RFC822/SMTP, A=IPC $h Mlocal, P=/bin/mail, F=lsDFMAw5:/|@rmn, S=0, R=0, A=mail -d $u from $: in rule set 0
Rule set 0 is different from the other rule sets in several important ways. We'll begin explaining the other rule sets in the next chapter. For now, just be aware that there are a few exceptions to rules in sendmail:
Rule set 0 is one of the few rule sets that may use $#
to return the
symbolic name of a delivery agent.
[2]
If any other rule set returns
a $#
, the $#
can cause unpredictable errors.
[2] Rule set 5 can also return a
$#
.
$@
and $:
in rule set 0, when
following $#
, have different meanings than
they do in all the other rule sets. They are even different from the
way they are
in rule set 0 itself when they don't follow $#
.
We'll expand on this concept in the next chapter.