The -list switch tells mhbuild to list the table of contents associated with the MIME message that is created.

The -headers switch indicates that a one-line banner should be displayed above the listing. The -realsize switch tells mhbuild to evaluate the “native” (decoded) format of each content prior to listing. This provides an accurate count at the expense of a small delay. If the -verbose switch is present, then the listing will show any “extra” information that is present in the message, such as comments in the “Content-Type” header.

mhbuild is essentially a filter to aid in the composition of MIME messages. mhbuild will convert an mhbuild “composition file” into a valid MIME message. A mhbuild “composition file” is just a file containing plain text that is interspersed with various mhbuild directives. When this file is processed by mhbuild, the various directives will be expanded to the appropriate content, and will be encoded according to the MIME standards. The resulting MIME message can then be sent by electronic mail.

The formal syntax for a mhbuild composition file is defined at the end of this document, but the ideas behind this format are not complex. Basically, the body contains one or more contents. A content consists of either a directive, indicated with a “#” as the first character of a line; or, plaintext (one or more lines of text). The continuation character, “\“, may be used to enter a single directive on more than one line, e.g.,

#image/png \
    /home/foobar/junk/picture.png

There are four kinds of directives: “type” directives, which name the type and subtype of the content; “external-type” directives, which also name the type and subtype of the content; the “message” directive (#forw), which is used to forward one or more messages; and, the “begin” directive (#begin), which is used to create a multipart content.

The “type” directive is used to directly specify the type and subtype of a content. You may only specify discrete types in this manner (can't specify the types multipart or message with this directive). You may optionally specify the name of a file containing the contents in “native” (decoded) format. If this filename starts with the “|” character, then it represents a command to execute whose output is captured accordingly. For example,

#audio/basic |raw2audio -F < /usr/lib/sound/giggle.au

If a filename is not given, mhbuild will look for information in the user's profile to determine how the different contents should be composed. This is accomplished by consulting a composition string, and executing it under /bin/sh, with the standard output set to the content. If the -verbose switch is given, mhbuild will echo any commands that are used to create contents in this way.

The composition string may contain the following escapes:

%a	Insert parameters from directive
%f	Insert filename containing content
%F	%f, and stdout is not re-directed
%s	Insert content subtype
%%	Insert character %

First, mhbuild will look for an entry of the form:

mhbuild-compose-<type>/<subtype>

to determine the command to use to compose the content. If this isn't found, mhbuild will look for an entry of the form:

mhbuild-compose-<type>

to determine the composition command. If this isn't found, mhbuild will complain.

An example entry might be:

mhbuild-compose-audio/basic: record | raw2audio -F

Because commands like these will vary, depending on the display environment used for login, composition strings for different contents should probably be put in the file specified by the $MHBUILD environment variable, instead of directly in your user profile.

The “external-type” directives are used to provide a MIME reference to a content, rather than enclosing the contents itself (for instance, by specifying an ftp site). Hence, instead of providing a filename as with the type directives, external-parameters are supplied. These look like regular parameters, so they must be separated accordingly. For example,

#@application/octet-stream; \
    type=tar; \
    conversions=compress \
    [this is the nmh distribution] \
    name="nmh.tar.gz"; \
    directory="/pub/nmh"; \
    site="ftp.math.gatech.edu"; \
    access-type=anon-ftp; \
    mode="image"

You must give a description string to separate the content parameters from the external-parameters (although this string may be empty). This description string is specified by enclosing it within “[]”.

These parameters are of the form:

access-type=	usually anon-ftp or mail-server
name=	filename
permission=	read-only or read-write
site=	hostname
directory=	directoryname (optional)
mode=	usually ascii or image (optional)
size=	number of octets
server=	mailbox
subject=	subject to send
body=	command to send for retrieval

The “message” directive (#forw) is used to specify a message or group of messages to include. You may optionally specify the name of the folder and which messages are to be forwarded. If a folder is not given, it defaults to the current folder. Similarly, if a message is not given, it defaults to the current message. Hence, the message directive is similar to the forw command, except that the former uses the MIME rules for encapsulation rather than those specified in RFC-934. For example,

#forw +inbox 42 43 99

If you include a single message, it will be included directly as a content of type “message/rfc822”. If you include more than one message, then mhbuild will add a content of type “multipart/digest” and include each message as a subpart of this content.

If you are using this directive to include more than one message, you may use the -rfc934mode switch. This switch will indicate that mhbuild should attempt to utilize the MIME encapsulation rules in such a way that the “multipart/digest” that is created is (mostly) compatible with the encapsulation specified in RFC-934. If given, then RFC-934 compliant user-agents should be able to burst the message on reception0--0providing that the messages being encapsulated do not contain encapsulated messages themselves. The drawback of this approach is that the encapsulations are generated by placing an extra newline at the end of the body of each message.

The “begin” directive is used to create a multipart content. When using the “begin” directive, you must specify at least one content between the begin and end pairs.

#begin
This will be a multipart with only one part.
#end

If you use multiple directives in a composition draft, mhbuild will automatically encapsulate them inside a multipart content. Therefore the “begin” directive is only necessary if you wish to use nested multiparts, or create a multipart message containing only one part.

For all of these directives, the user may include a brief description of the content between the “[” character and the “]” character. This description will be copied into the “Content-Description” header when the directive is processed.

#forw [important mail from Bob] +bob 1 2 3 4 5

By default, mhbuild will generate a unique “Content-ID:” for each directive; however, the user may override this by defining the ID using the “<” and “>” characters.

In addition to the various directives, plaintext can be present. Plaintext is gathered, until a directive is found or the draft is exhausted, and this is made to form a text content. If the plaintext must contain a “#” at the beginning of a line, simply double it, e.g.,

##when sent, this line will start with only one #

If you want to end the plaintext prior to a directive, e.g., to have two plaintext contents adjacent, simply insert a line containing a single “#” character, e.g.,

this is the first content
#
and this is the second

Finally, if the plaintext starts with a line of the form:

Content-Description: text

then this will be used to describe the plaintext content. You MUST follow this line with a blank line before starting your text.

By default, plaintext is captured as a text/plain content. You can override this by starting the plaintext with “#<” followed by a content-type specification. For example, e.g.,

#<text/enriched
this content will be tagged as text/enriched
#
and this content will be tagged as text/plain
#
#<application/x-patch [this is a patch]
and this content will be tagged as application/x-patch

Note that if you use the “#<” plaintext-form, then the content-description must be on the same line which identifies the content type of the plaintext.

When composing a text content, you may indicate the relevant character set by adding the “charset” parameter to the directive.

#<text/plain; charset=iso-8859-5

If a text content contains any 8-bit characters (characters with the high bit set) and the character set is not specified as above, then mhbuild will assume the character set is of the type given by the environment variable MM_CHARSET. If this environment variable is not set, then the character set will be labeled as “x-unknown”.

If a text content contains only 7-bit characters and the character set is not specified as above, then the character set will be labeled as “us-ascii”.

Putting this all together, here is an example of a more complicated message draft. The following draft will expand into a multipart/mixed message containing five parts:

To: nobody@nowhere.org
cc:
Subject: Look and listen to me!
--------
The first part will be text/plain
#<text/enriched
The second part will be text/enriched
#
This third part will be text/plain
#audio/basic [silly giggle]  \
    |raw2audio -F < /usr/lib/sounds/giggle.au
#image/gif   [photo of foobar] \
                    /home/foobar/lib/picture.gif

If Imhbuild is given the -check switch, then it will also associate an integrity check with each “leaf” content. This will add a Content-MD5 header field to the content, along with the md5 sum of the unencoded contents. This may be used by the receiver of the message to verify that the contents of the message were not changed in transport.

After mhbuild constructs the new MIME message by parsing directives, including files, etc., it scans the contents of the message to determine which transfer encoding to use. It will check for 8bit data, long lines, spaces at the end of lines, and clashes with multipart boundaries. It will then choose a transfer encoding appropriate for each content type.

If an integrity check is being associated with each content by using the -check switch, then mhbuild will encode each content with a transfer encoding, even it the content contains only 7-bit data. This is to increase the likelihood that the content is not changed while in transport.

The switch -ebcdicsafe will cause mhbuild to slightly change the way in which it performs the “quoted-printable” transfer encoding. Along with encoding 8-bit characters, it will now also encode certain common punctuation characters as well. This slightly reduces the readability of the message, but allows the message to pass more reliably through mail gateways which involve the EBCDIC character encoding.

Typically, mhbuild is invoked by the whatnow program. This command will expect the body of the draft to be formatted as an mhbuild composition file. Once you have composed this input file using a command such as comp, repl, or forw, you invoke mhbuild at the “What now” prompt with

What now? mime

prior to sending the draft. This will cause whatnow to execute mhbuild to translate the composition file into MIME format.

It is also possible to have the whatnow program invoke mhbuild automatically when a message is sent. To do this, you must add the line

automimeproc: 1

to your .mhprofile file.

Finally, you should consider adding this line to your profile:

lproc: show

This way, if you decide to list after invoking mime, the command

What now? list

will work as you expect.

Because the environment in which mhbuild operates may vary for a user, mhbuild will look for the environment variable $MHBUILD. If present, this specifies the name of an additional user profile which should be read. Hence, when a user logs in on a particular machine, this environment variable should be set to refer to a file containing definitions useful for that machine.

Finally, mhbuild will attempt to consult a global mhbuild user profile, e.g.,

/etc/nmh/mhn.defaults

if it exists.

The following is the formal syntax of a mhbuild “composition file”.

body         ::=     1*(content | EOL)

content ::= directive | plaintext

directive ::= "#" type "/" subtype 0*(";" attribute "=" value) [ "(" comment ")" ] [ "<" id ">" ] [ "[" description "]" ] [ filename ] EOL

| "#@" type "/" subtype 0*(";" attribute "=" value) [ "(" comment ")" ] [ "<" id ">" ] [ "[" description "]" ] external-parameters EOL

| "#forw" [ "<" id ">" ] [ "[" description "]" ] [ "+"folder ] [ 0*msg ] EOL

| "#begin" [ "<" id ">" ] [ "[" description "]" ] [ "alternative" | "parallel" | something-else ] EOL 1*body "#end" EOL

plaintext ::= [ "Content-Description:" description EOL EOL ] 1*line [ "#" EOL ]

| "#<" type "/" subtype 0*(";" attribute "=" value) [ "(" comment ")" ] [ "[" description "]" ] EOL 1*line [ "#" EOL ]

line ::= "##" text EOL -- interpreted as "#"text EOL | text EOL