mh-alias (5mh)

Each line of an nmh alias file takes one of the following forms:

alias : address-group

alias ; address-group

< alias-file

; | : | # comment

where:

address-group	:= address-list
			|  < file
			|  = UNIX-group
			|  + UNIX-group
			|  *

address-list	:= address
			|  address-list, address

Continuation lines end with “\” followed by a newline character. This also applies to comment lines. Thus, the line following a “\”-terminated comment line is a continuation of that comment line.

Alias-file and file are UNIX file names. UNIX-group is a group name or number from the system's group database. Alias file contents are case-insensitive, with the exception of filesystem path names.

If the line starts with a “<”, 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 “<”, 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 “=”, the system's group database 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 “+”, the system's group database is consulted to determine the group-id of the UNIX-group named after the “+”. Each login name occurring in the system's password database whose group-id is indicated by this group is added to the address-list for the alias.

If the address-group is simply “*”, the system's password database 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. This feature is obsolescent and will be removed in a future release.

In match, a trailing “*” on an alias will match just about anything appropriate.

An approximation of the way aliases are resolved at posting time is:

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 (with the alias quoted if necessary and the address wrapped in <>).

Since the mh-alias file is read line by line, forward references work, but backward references are not recognized.

Example Alias File

</etc/nmh/BBoardAliases
fred: [email protected]
sgroup: fred, fear, freida
b-people: Blind List: bill, betty
UNIX-committee: <unix.aliases
staff: =staff
wheels: +wheel
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 “[email protected]”, and “sgroup” is defined as an alias for the three names “[email protected]”, ”fear”, and ”freida”.

The alias “b-people” is a blind list which includes the addresses “bill” and “betty”; the message will be delivered to those addresses, but the message header will show only “Blind List: ;” (not the addresses). The alias must not be terminated with, or contain, a semicolon. Note that blind lists are not supported with the sendmail/pipe mail transport method.

Next, the definition of “UNIX-committee” is given by reading the file unix.aliases in the user's nmh directory, “staff” is defined as all users who are listed as members of the group “staff” in the system's group database, and “wheels” is defined as all users whose group-id in the system's password database is equivalent to the “wheel” group.

Aliasfile:

Default alias file.

/etc/nmh/MailAliases

System-wide default alias file.

ali(1), send(1), whom(1), getgrent(3), getpwent(3), conflict(8), post(8)

Although the forward-referencing semantics of mh-alias files prevent recursion, the alias-file directive may defeat this. Since the number of file descriptors is finite, such infinite recursion will terminate with a meaningless diagnostic when all the fds are used up.

Earlier versions of this man page showed a semicolon at the end of the blind list example. That caused the preceding alias to not be expanded. There must not be a semicolon at the end of, or within, the address group of a blind list. post will append the semicolon to the blind list name.