MH-ALIAS(5)
NAME
mh-alias - alias file for nmh message system
SYNOPSIS
any nmh command
DESCRIPTION
This describes both nmh personal alias files and the
global alias file for nmh mail delivery, the file
/etc/nmh/MailAliases
It does not describe aliases files used by the message
transport system. Each line of the alias file has the
format:
alias : address-group
or
alias ; address-group
or
< alias-file
or
; comment
where:
address-group := address-list
| "<" file
| "=" UNIX-group
| "+" UNIX-group
| "*"
address-list := address
| address-list, address
Continuation lines in alias files end with `\' followed by
the newline character.
Alias-file and file are UNIX file names. UNIX-group is a
group name (or number) from /etc/group. An address is a
"simple" Internet-style address. Througout this file,
case is ignored, except for alias-file names.
If the line starts with a `<', then the file named after
the `<' is read for more alias definitions. The reading
is done recursively, so a `<' may occur in the beginning
of an alias file with the expected results.
If the address-group starts with a `<', then the file
named after the `<' is read and its contents are added to
the address-list for the alias.
If the address-group starts with an `=', then the file
/etc/group is consulted for the UNIX-group named after the
`='. Each login name occurring as a member of the group
is added to the address-list for the alias.
In contrast, if the address-group starts with a `+', then
the file /etc/group is consulted to determine the group-id
of the UNIX-group named after the `+'. Each login name
occurring in the /etc/passwd file whose group-id is indi-
cated by this group is added to the address-list for the
alias.
If the address-group is simply `*', then the file
/etc/passwd is consulted and all login names with a userid
greater than some magic number (usually 200) are added to
the address-list for the alias.
In match, a trailing * on an alias will match just about
anything appropriate. (See example below.)
An approximation of the way aliases are resolved at post-
ing time is (it's not really done this way):
1) Build a list of all addresses from the message to
be delivered, eliminating duplicate addresses.
2) If this draft originated on the local host, then
for those addresses in the message that have no host
specified, perform alias resolution.
3) For each line in the alias file, compare "alias"
against all of the existing addresses. If a match,
remove the matched "alias" from the address list, and
add each new address in the address-group to the
address list if it is not already on the list. The
alias itself is not usually output, rather the
address-group that the alias maps to is output
instead. If "alias" is terminated with a `;' instead
of a `:', then both the "alias" and the address are
output in the correct format. (This makes replies
possible since nmh aliases and personal aliases are
unknown to the mail transport system.)
Since the alias file is read line by line, forward refer-
ences work, but backward references are not recognized,
thus, there is no recursion.
Example:
</etc/nmh/BBoardAliases
sgroup: fred, fear, freida
b-people: Blind List: bill, betty;
fred: frated@UCI
UNIX-committee: <unix.aliases
staff: =staff
wheels: +wheel
everyone: *
news.*: news
The first line says that more aliases should immediately
be read from the file /etc/nmh/BBoardAliases. Following
this, "fred" is defined as an alias for "frated@UCI", and
"sgroup" is defined as an alias for the three names
"frated@UCI", "fear", and "freida".
The alias "b-people" is a blind list which includes the
addresses "bill" and "betty"; the message will be delieved
to those addresses, but the message header will show only
"Blind List: ;" (not the addresses).
Next, the definition of "UNIX-committee" is given by read-
ing the file unix.aliases in the users nmh directory,
"staff" is defined as all users who are listed as members
of the group "staff" in the /etc/group file, and "wheels"
is defined as all users whose group-id in /etc/passwd is
equivalent to the "wheel" group.
Finally, "everyone" is defined as all users with a user-id
in /etc/passwd greater than 200, and all aliases of the
form "news.<anything>" are defined to be "news".
The key thing to understand about aliasing in nmh is that
aliases in nmh alias files are expanded into the headers
of messages posted. This aliasing occurs first, at post-
ing time, without the knowledge of the message transport
system. In contrast, once the message transport system is
given a message to deliver to a list of addresses, for
each address that appears to be local, a system-wide alias
file is consulted. These aliases are NOT expanded into
the headers of messages delivered.
HELPFUL HINTS
To use aliasing in nmh quickly, do the following:
First, in your .mh_profile, choose a name for your
alias file, say "aliases", and add the line:
Aliasfile: aliases
Second, create the file "aliases" in your nmh direc-
tory.
Third, start adding aliases to your "aliases" file as
appropriate.
FILES
/etc/nmh/MailAliases global nmh alias file
PROFILE COMPONENTS
Aliasfile: For a default alias file
SEE ALSO
ali(1) send(1) whom(1) group(5) passwd(5) con-
flict(8) post(8)
DEFAULTS
None
CONTEXT
None
BUGS
Although the forward-referencing semantics of mh-alias
files prevent recursion, the "< alias-file" command may
defeat this. Since the number of file descriptors is
finite (and very limited), such infinite recursion will
terminate with a meaningless diagnostic when all the fds
are used up.
Forward references do not work correctly inside blind
lists.