Some variables and attributes with the type of string are really lists of items (such as hostnames, hostname regular expressions, IP addresses, etc.). Lists are normally simply colon (:) separated values. Generally the colon may be preceded and/or followed by arbitrary whitespace, though of course in an attribute value (i.e. anywhere except in the config file) this means the value must be quoted or the whitespace characters must be each escaped with a backslash (\).

In some cases an optional semicolon (;) separated sub-field may be given to given with an item value as well. In that case the first sub-field is the primary item value and the second sub-field is, in most cases, a string treated as an error message or other descriptive text to be associated with the item. Note that the message text is not quoted (and is not separately quotable) so it must not contain another colon (`:') character. Escape processing as described above cannot protect a field separator. Note that in an attribute definition (i.e. anywhere except in the config file, though currently no attributes allow sub-fields) if you use the semicolon separator to specify a sub-field then you must either escape it with a backslash or enclose the entire attribute definition in double quotes. The text message may contain semicolons itself though since it extends to the end of the field (i.e. to the next colon (`:') character).

Items in a list of hostnames or IP addresses may be negated by prefixing them with an exclamation mark (!). When some value is being compared to the items in the list then a match of a negated item will cause the remainder of the items in the list to be ignored and for a no-match condition to be immediately indicated (thus implementing a ``first match wins'' algorithm). For example in a list of IP addresses the following would match any address in the range 10.0.0.0 through 10.255.255.255 except 10.1.1.1:

    ! 10.1.1.1 : 10/8

As mentioned above some lists may contain strings representing IP addresses. They are specified in a format compatible with inet_net_pton(3). Generally speaking this means a host may be specified in the standard four-octet ASCII form, and any CIDR network may be specified by a four-octet number follwed by a slash (`/') and a number specifying the number of bits in the network portion.

The magic keyword localnet represents a run-time generated pattern constructed to represent the classical IP network for the local address of the current connection. This keyword is of little use to anyone using either a supernet, or a subnet of anything larger than a Class C (/24) network.

Optionally if smail has been compiled with ``HAVE=LIBWHOSON'' then there is also support for a magic keyword whoson which can be used to query a WHOSON server for additonal IP numbers which are currently authorised to relay mail remotely via SMTP.

As mentioned above some lists may contain hostname regular expressions. These are simply regular expression strings which are matched against hostnames. The expression is implicitly anchored at the beginning and end of the hostname.

Note that the backslash character (`\') must be quoted with itself since it is also the escape character for all configuration entries.

Note that a case-insensitive match is always done if the host platform's underlying regular expression library is POSIX compliant.

Conditionals can be used to include text based on whether or not a particular value is non-empty. Conditionals are of the form:

    ${if condition [:] string}

    ${if condition {string1} {string2}}

Possible conditions are:

!condition

Negate the boolean value of condition.

def:variable

True if the given expansion variable is defined and is non-empty.

header:header

True if the message contains a header field named header.

origin:local

True if the message originated locally.

origin:remote

True if the message was received from a remote machine.

dest:local

True if the message is being delivered to an address on the local host.

dest:remote

True if the message is being delivered to a remote host.

xform:transformation

True if the transformation being applied to the message, for delivery by the assigned transport, matches the given type. Valid types are: local, inet, uucp, or none.

eq{variable}{string}

True if the given expansion of variable matches the given string.

gt{variable}{string}

True if the given expansion of variable is lexicographically greater than the given string.

lt{variable}{string}

True if the given expansion of variable is lexicographically less than the given string.

or{{ condition } ... }

True if any of the given conditions are true.

and{{ condition } ... }

True if all of the given conditions are true.

String expansions can use lookup procedures to convert a key, taken from a an expansion variable, into a string found in a file or other accessible database. These expansions are defined using the form:

    ${lookup:variable:proto{file-expansion}\
           [:]then-clause}

    ${lookup:variable:proto{file-expansion}\
            [then] {then-clause}\
            [else] {else-clause}}

Lookups operate by taking the value of the indicated variable as a key for lookup in a file. The proto string defines how the lookup is to be performed, and file-expansion is a string defining the file or database to search. If the key is found, then the then-clause is expanded, otherwise the else-clause is expanded. A $value reference in either clause is replaced by the value found by the lookup. For readability, the word then can be inserted before the then-clause, and the word else can be inserted before the else-clause.

Allowed lookup methods are:

bsearch

Use a binary search to locate the key in a sorted file, organised as lines beginning with a key separated from a value by blanks.

lsearch

Use a linear search to locate the key in a plain file, again organised as lines beginning with a key separated from a value by blanks.

Comments in this file begin with `#' and continue until end-of-line. Blank lines are ignored.

If Smail has been compiled with ``MISC_DEFINES=USE_LSEARCH_REGEXCMP'' then a line where the first field is surrounded in double quotes ("") specifies a regular expression (without the quotes) against which the key is matched using the host platform's underlying regular expression library.

dbm

Look up the key in a dbm database.

yp

Look up the key in a Sun NIS database.

aliasyp

Look up the key in a Sun NIS database. This differs from yp in that a NUL byte is added to the end of the key before lookup.

nialias

Look up the key in a NeXT netinfo database.

nisplus

Look up the key in a Sun NIS+ (Sun NIS Version 3) database. NIS+ is not compatible with NIS (otherwise known as YP). The file expansion parameter must be a NIS+ indexed name. The lookup routine within smail allows you to prepend the file-expansion with a string like ``@2,'' to use field number 2 from the result instead of using field 1 by default.

The complete set of available variable names depends upon context, but the following are always available:

compile_date

ld_date

the date when the current smail binary was compiled.

compile_num

ld_num

a decimal number giving the number of times smail has been compiled since the creation of the source file src/ldinfo.c.

ctime

the date and time, in the form returned by the ctime(3) function.

date

The date and time in ARPAnet (RFC 822) format.

spool_date

The date and time that the message was received by the local host, in ARPAnet (RFC 822) format.

grade

The priority character for the current message. See the grades attribute in the smailconf(X_MAN_5_EXT) manual for more information on this value.

ident_sender

The identification code of the user that sent the mail over its last hop as determined by the RFC 1413 protocol (other protocols may be added in future versions). This will generally only be set for mail received by SMTP. It is most useful for putting into the Received: message header field. This string has a null value if no sender-ID can be determined.

ident_method

The identification method used to generate the ident_sender. Currently this will always be ``rfc1413''.

This variable will be null if ident_sender is also null.

message_id

id

the message-ID for the current message.

message_size

size

the total size of the spooled message.

message_body_size

body_size

the size of the body of the message, which excludes the message header fields, and also excludes any overhead within the message spool file.

pid

$

the current process-ID.

primary_name

primary

the canonical name for the local host.

release_date

release

the release date of the smail sources.

sender

from

the address of the sender of a message.

sender_name

fullname

the full-name of the sender, taken either from the ``-F'' command line argument, or from the password file.

sender_host

the sending host, if one is known. This is set automatically for mail received via UUCP or SMTP. It can also be set with ``-oMs'' from the command line.

sender_host_address

the sending host's address, if one is known. This is set automatically for mail received via SMTP. It can also be set with ``-oMa'' from the command line.

sender_proto

the sending protocol (e.g. ``smtp'' or ``uucp''), if one is known. This is set automatically for mail received via UUCP or SMTP. It can also be set with ``-oMr'' from the command line.

sender_program

The program that queued the message. For mail received via UUCP, this will be, typically, ``rmail''. Otherwise, the sender program will likely by set to ``sendmail'' or ``smail'', depending upon the program that typically is invoked for receiving mail.

uucp_name

the UUCP-network name for the local host.

version

a short version string for Smail.

version_string

a verbose version string.

visible_name

name

the local host name used in outgoing addresses.

smail_lib_dir

lib_dir

the value of the config file variable smail_lib_dir, which is the directory in which configuration files are found.

In addition, the following variables are defined if they are available in the current context:

HOME

home

the home directory of a user associated with an address.

host

the remote host string associated with a remote address.

local_domain

The local domain an address may have matched, if it matched a local domain.

user

addr

a user name or remaining local part of the address after all rewriting.

user_prefix

any string matching the regular expression given in the optional prefix attribute of a director instance using the user director driver.

user_suffix

any string matching the regular expression given in the optional suffix attribute of a director instance using the user director driver.

input_addr

The address specified in the message, or in an alias or mailing list expansion, that is being processed.

mailbox

The ``local part'' of the input address.

route

Any route specification from the input address.

director

The name of the director that matched the address, if appropriate.

router

The name of the router that matched the address, if appropriate.

transport

The name of the transport to be used for delivering to the address, if the address has been successfully resolved.

The following modifiers are available for meta-expansions. Note that multiple modifiers can be specified and that they are interpreted strictly from left to right.

eval

expand all variable expansions, file lookups, etc. in specified variable. (This is probably only useful when used on the command line with -bP.)

lc

convert to lower case.

parent

interpret the value within the context of the parent local address that produced the associated address. This is useful when the local address that produced an address is desired. Expansion fails if no parent exists.

quote

enclose the value in quotes, if it would not otherwise be a valid local-form address, within the rules of RFC 822. Uses backslash escapes as appropriate.

rxquote

make the whole string only match exactly when used as a regular expression (RE) by properly escaping any RE meta-characters. This can be used when expanding lists of hostnames within other lists, for example.

shquote

make the value of a variable into a single quoted string (i.e. one shell argument), and properly escape any internal quote characters. This tidies up a variable value that may have been supplied from an untrusted source to allow it to be passed to a shell command without nasty effects. Note that you only have to use ``${shquote:'' on string values that will be passed as arguments on a shell command line. In some cases even the pipe driver does not use the shell.

strip

Remove backslashes and double quotes from a value. If a double-quote is preceded by a backslash, the backslash is removed, but the double quote is not. Sequences of whitespace characters and dots are converted to exactly one dot character.

top

interpret the value within the context of the original address, supplied to the mailer, that produced the associated address.

uc

convert to upper case.

The following are sample string expansions:

    /usr/spool/mail/${lc:user}

    /usr/spool/mail/tron

    Received: by $primary_name ($version_string) 
              id <$message_id@primary_name>;
              $spool_date

    Received: by futatsu.uts.amdahl.com (smail 3.0.2 03-dec-87) 
              id <m0c87zK-007zXpC@futatsu.uts.amdahl.com>;
              Tue, 8 Dec 87 19:45 PST

    $host!rmail ${strip:addr}

    amdahl!rmail Ronald.S.Karr

    smart_user="|/bin/mquery -f ${shquote:lc:sender} ${shquote:lc:user}"

    Foo';rm /etc/passwd;'

    |/bin/mquery -f 'foo'"'"';rm /etc/passwd;'"'"'' 'got ya!'

If a value does not exist (such as $HOME being used when no associated home directory is known, or when a string begins with ``~username'' and ``username'' is not a known use, or when $host is used for a local address) then the expansion fails.