usr.sbin/sendmail/cf/m4/rule3.m4

divert(10)
#
#  Sendmail
#  Copyright (c) 1983  Eric P. Allman
#  Berkeley, California
#
#  Copyright (c) 1983 Regents of the University of California.
#  All rights reserved.  The Berkeley software License Agreement
#  specifies the terms and conditions for redistribution.
#
#       @(#)rule3.m4    1.17 (Berkeley) 1/3/89
#
divert(0)
###########################
#  Name Canonicalization  #
###########################
S3

# handle "from:<>" special case
R$*<>$*                 $@@                             turn into magic token

# basic textual canonicalization -- note RFC733 heuristic here
R$*<$*<$*<$+>$*>$*>$*   $4                              3-level <> nesting
R$*<$*<$+>$*>$*         $3                              2-level <> nesting
R$*<$+>$*               $2                              basic RFC821/822 parsing

# make sure <@a,@b,@c:user@d> syntax is easy to parse -- undone later
R@$+,$+                 @$1:$2                          change all "," to ":"

# localize and dispose of route-based addresses
R@$+:$+                 $@$>6<@$1>:$2                   handle <route-addr>

# more miscellaneous cleanup
R$+                     $:$>8$1                         host dependent cleanup
R$+:$*;@$+              $@$1:$2;@$3                     list syntax
R$+:$*;                 $@$1:$2;                        list syntax
R$+@$+                  $:$1<@$2>                       focus on domain
R$+<$+@$+>              $1$2<@$3>                       move gaze right
R$+<@$+>                $@$>6$1<@$2>                    already canonical

# convert old-style addresses to a domain-based address
R$+^$+                  $1!$2                           convert ^ to !
R$-!$+                  $@$>6$2<@$1.UUCP>               resolve uucp names
R$+.$-!$+               $@$>6$3<@$1.$2>                 domain uucps
R$+!$+                  $@$>6$2<@$1.UUCP>               uucp subdomains
R$+%$+                  $:$>9$1%$2                      user%host
R$+<@$+>                $@$>6$1<@$2>                    already canonical
R$-.$+                  $@$>6$2<@$1>                    host.user


#################################
#   special local conversions   #
#################################

S6
R$*<@$=w>$*             $:$1<@$w>$3                     get into u@$w form
R$*<@$=w.$D>$*          $:$1<@$w>$3
R$*<@$=U.UUCP>$*        $:$1<@$w>$3

################################
#   Change rightmost % to @.   #
################################

S9
R$*%$*                  $1@$2                           First make them all @'s.
R$*@$*@$*               $1%$2@$3                        Undo all but the last.
R$*@$*                  $@$1<@$2>                       Put back the brackets.