MAN page from RedHat Other mh-6.8.3-15.i386.rpm

MH-ALIAS

Section: File Formats (5)
Updated: MH.6.8
Index

NAME

mh-alias - alias file for MH message system

SYNOPSIS

any MH command

DESCRIPTION

This describes both MH personal alias files andthe (primary) alias file for mail delivery, the file

/usr/lib/mh/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 newlinecharacter.

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 `<' isread 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 tothe address-list for the alias.

If the address-group starts with an `=',then the file /etc/group is consultedfor the UNIX-group named after the `='.Each login name occurring as a member of the group is added to theaddress-list for the alias.

In contrast, if the address-group starts with a `+',then the file /etc/group is consultedto determine the group-id of the UNIX-group named after the `+'.Each login name occurring in the /etc/passwd file whose group-idis indicated by this group is added to the address-list for the alias.

If the address-group is simply `*',then the file /etc/passwd is consultedand 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 posting time is(it's not really done this way):

1) Build a list of all addresses from the message to bedelivered, 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 listif 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 outputin the correct format.(This makes replies possible since MH aliases andpersonal aliases are unknown to the mail transport system.)

Since the alias file is read line by line, forward referenceswork, but backward references are not recognized, thus, there isno recursion.

Example:

</usr/lib/mh/BBoardAliasessgroup: fred, fear, freidab-people: Blind List: bill, betty;fred: frated@UCIUNIX-committee: <unix.aliasesstaff: =staffwheels: +wheeleveryone: *news.*: news

The first line says that more aliases should immediately be read fromthe file /usr/lib/mh/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 theaddresses ``bill'' and ``betty''; the messagewill be delieved to those addresses, but themessage header will show only ``Blind List: ;'' (not the addresses).

Next, the definition of ``UNIX-committee'' is given by readingthe file unix.aliases in the users MH directory,``staff'' is defined as all users who are listed as members ofthe 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 definedto be ``news''.

The key thing to understand about aliasing in MHis that aliases in MH alias files are expanded into theheaders of messages posted.This aliasing occurs first,at posting time,without the knowledge of the message transport system.In contrast,once the message transport system is given a message to deliverto 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.To use aliasing in MH 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 MH directory.

Third, start adding aliases to your ``aliases'' file as appropriate.^/usr/lib/mh/MailAliases~^Primary alias file^Aliasfile:~^For a default alias fileali(1), send(1), whom(1), group(5), passwd(5), conflict(8), post(8)NoneNoneIn previous releases of MH,only a single, system-wide mh-alias file was supported.This led to a number of problems,since only mail-system administrators were capable of (un)definingaliases.Hence,the semantics of mh-alias were extended to support personal alias files.Users of MH no longer need to bother mail-system administrators forkeeping information in the system-wide alias file,as each MH user can create/modify/remove aliases at will from anynumber of personal files.Although the forward-referencing semantics of mh-alias files preventrecursion, the ``< alias-file'' command may defeat this. Since thenumber of file descriptors is finite (and very limited), such infiniterecursion will terminate with a meaningless diagnostic when all the fds areused up.

Forward references do not work correctly inside blind lists.

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