METAMAIL(1) Bellcore Prototype (Release 2) METAMAIL(1)
NAME
metamail - infrastructure for mailcap-based multimedia mail
handling
SYNOPSIS
metamail[-b] [-B] [-c contenttype ...] [-d] [-e] [-E
contentencoding] [-f from-name] [-h] [-m mailer-name] [-p]
[-P] [-r] [-s subject] [-q] [-w] [-x] [-y] [-z] [file-name]
DESCRIPTION
The metamail program reads a "mailcap" file to determine how
to display non-text at the local site. Every mail-reading
interface needs to call metamail whenever non-text mail is
being viewed, unless the mail is of a type that is already
understood by the mail-reading program. Metamail consults
the mailcap file(s) to determine what program to use to show
the message to the user.
At a site where all mail reading interfaces have been
modified to call metamail for non-text mail, extending the
local email system to handle a new media type in the mail
becomes a simple matter of adding a line to a mailcap file.
(Although this manual page will discuss only mail, metamail
is equally useful in adding multimedia support to news and
bulletin board reading programs, assuming those programs
preserve the "Content-type" header or some other indication
of the content type of the messages.)
In general, users will never run metamail directly.
Instead, metamail will be invoked for the user automatically
by the user's mail reading program, whenever a non-text
message is to be viewed. This manual page, therefore, is
directed not at end users, but at two categories of readers:
those who are adding metamail support to a particular mail-
reading program, and those who are adding lines to a mailcap
file. The former need only to be concerned with the command
line syntax of metamail. The latter may
ignore the command line syntax, and need only be concerned
with the mailcap file syntax, as described in a later
section.
Note: Metamail determines the type of a message using the
"Content-type" header, as defined in RFC 1049 and RFC-1341
(MIME). However, using the -b and -c options, metamail can
be made to work with mail that is not in Internet format,
including X.400 messages. Note also that metamail
automatically decodes mail that has been encoded for 7 bit
transport if the mail includes a Content-Transfer-Encoding
header as specified by RFC-1341. If data has been encoded
via the "base64" encoding, it will map CRLF to local
newlines for textual data, but not for other data, unless
instructed otherwise by a "textualnewlines" field in a
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METAMAIL(1) Bellcore Prototype (Release 2) METAMAIL(1)
mailcap entry.
OPTIONS
When called with no options or arguments, metamail expects
to receive an RFC 822 format message on its standard input.
The following options can alter that expectation:
-b This option tells metamail that the message is not
in RFC 822 format, but instead is only the body of
the message (i.e. there are no message headers).
The use of -b requires the use of -c.
-B This option tells metamail that the message is to be
displayed in the background, if it is non-
interactive (i.e. it doesn't have the
"needsterminal" attribute in the mailcap file). It
cannot be used with -p or -P.
-c <contenttype>
This option tells metamail to use the specified
content type rather than the one in the headers, if
any.
-d This option tells metamail not to ask any questions
before running an interpreter to view the message.
(By default, metamail always asks before running
almost any interpreter, if it is running in an
interactive terminal and the MM_NOASK environment
variable is not set. However, it does not ask about
the content-type "text" -- that is, the default
value for MM_NOASK is "text,text/us-ascii")
-e This option tells metamail to "eat" leading newlines
in message bodies. This is particularly useful for
MH-format mail.
-f <address>
This option specifies the name of the sender of the
message. Otherwise, this is determined from the
header, if possible. This information will be
placed in the environment to make it available to
any interpreters called by metamail.
-h This option specifies that metamail is being used
for printing a message. In particular, this means
that the normal mailcap "command" field will not be
executed, but instead the command specified in the
"print" field will be executed. (If there is
nothing in the print field, the mailcap entry will
be ignored and the search will continue for a
matching mailcap entry that does have a print
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field.) The -h option automatically turns on the -d
option.
-m <mailername>
This option specifies the name of the mail program
that called metamail. This information will be
placed in the environment to make it available to
any interpreters called by metamail.
-p This option specifies that, if necessary, output
should be shown to the user one page at a time. By
default, this will cause such output to be piped
through the "more" command, but the environment
variable METAMAIL_PAGER can be used to specify an
alternative command to use. Note that one should
use -p rather than piping the output of metamail
through a pager, because some interpreters called by
metamail might be interactive rather than requiring
pagination. Metamail can tell whether or not to use
a page r from information in the mailcap file. This
option cannot be used with -B.
-P This option is just like -p, except that it also
causes metamail to print "Press RETURN to go on" and
await a RETURN after it has finished with the
message. This is intended for use only when
metamail calls itself recursively in a new terminal
window created only for that purpose. This option
cannot be used with -B.
-q This option tells metamail to be quiet. By default,
metamail prints a few key message headers
(controllable with the KEYHEADS and KEYIGNHEADS
environment variables) and some other informative
information, on stdout before running the
interpreter, but this behavior is suppressed with
-q.
-r This option specifies that it is OK to run as root.
By default, metamail refuses to run if the real or
effective user id is root. You can get the same
effect using the MM_RUNASROOT environment variable.
-R This option specifies that the /usr/ucb/reset should
be executed to reset the terminal state, before any
other I/O activity.
-s <subject>
This option specifies the subject of the mail
message. By default, this information is obtained
from the headers. This information will be placed
in the environment to make it available to any
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interpreters called by metamail.
-w This option tells metamail that instead of
consulting a mailcap file to decide how to display
the data, it should simply decode each part and
write it to a file in its raw (possibly binary)
format. Depending on the circumstances in which it
is called, metamail may derive the file name to use
from the message headers, by asking the user, or by
generating a unique temporary file name.
-x This option tells metamail that it is definitely not
running on a terminal, no matter what isatty() says.
This is necessary when metamail is actually running
on a pseudoterminal and isatty(3) returns TRUE but
there's really no terminal on which to interact with
the user. The same effect as -x can also be
obtained with the environment variable MM_NOTTTY.
-y This option tells metamail to try to "yank" a MIME-
format message from the body of the message. It is
useful when a MIME-format has been rejected by a
mail delivery system that does not now how to format
the rejection in a MIME-compliant manner. (For the
convenience of those who can't control how metamail
is called from their mail reader, this can also be
set with the MM_YANKMODE variable.) If you use yank
mode on messages that really ARE in MIME format, or
on messages that do not contain a MIME message
in the body, the effects could be VERY strange. It
won't hurt you, but you won't see anything very
useful, either.
-z This option tells metamail to delete its input file
when finished. The -z option requires that a file
name was given as an argument to metamail, i.e. that
it is not reading stdin.
-T This option is intended to be used by metamail
recursively, to turn off the effect of the
MM_TRANSPARENT environment variable. It should only
be used when the metamail program restarts itself in
a terminal emulator window.
File Name Arguments
Any argument that does not start with "-" is
interpreted as the name of a file to read instead of
standard input.
UNRECOGNIZED MAIL TYPES
From time to time, metamail may tell you something like
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**** Unrecognized mail type: 'smell-o-vision'. Writing to
file /tmp/metamail.1234 ****
What this means is that your are trying to read a message
that contains data that is marked as being in "smell-o-
vision" format, but that your site has not yet configured
metamail to properly display that type of data. In the
general case, such configuration is accomplished using the
mailcap file mechanism, as described in the next section.
For unrecognized types, metamail simply removes all header
and encoding information from the data, and writes it out to
a temporary file. (If running interactively, it will give
you more alternatives -- writing it to a temporary file,
viewing it as text, or jus skipping it.) It is up to the
user to delete such files when he or she is through with
them.
THE MAILCAP FILE(S)
The primary purpose of the metamail program is to allow
diverse mail reading programs to centralize their access to
multimedia information. If all the mail reading programs
call a single program to handle non-text mail, then only
that program needs to know about the diverse types of non-
text mail that might be received.
The metamail program is made more flexible in this role
through the mechanism of one or more "mailcap" files. The
purpose of the mailcap files is to tell metamail what
program to run in order to show the user mail in a given
format. Thus it becomes possible to add a new media type to
all of the mail reading programs at a site simply by adding
a line to a mailcap file.
Metamail uses a search path to find the mailcap file(s) to
consult. Unlike many path searches, if necessary metamail
will read all the mailcap files on its path. That is, it
will keep reading mailcap files until it runs out of them,
or until it finds a line that tells it how to handle the
piece of mail it is looking at. If it finds a matching
line, it will execute the command that is specified in the
mailcap file.
The default search path is equivalent to
$HOME/.mailcap:/usr/local/etc/mailcap:/usr/etc/mailcap:/etc/mailcap:/etc/mail/mailcap:/usr/public/lib/mailcap"
It can be overridden by setting the MAILCAPS environment
variable. Note: Metamail does not actually interpret
environment variables such as $HOME or the "~" syntax in
this path search.
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The format of mailcap files is explained in the manual entry
for mailcap(4).
NON-ASCII HEADER FIELDS
Metamail has rudimentary built-in support for the emerging
Internet standards for non-ASCII data in mail headers. What
this means is that such data will be recognized, decoded,
and sent to the terminal. This behavior may be more or less
reasonable, depending on the character set in the header
data and the capability of the user's terminal, but it will
rarely be any worse than showing such data in its encoded
form.
ENVIRONMENT
METAMAIL_TMPDIR
If set, this variable overrides "/tmp" as the name
of the directory in which metamail and associated
programs will create temporary files on UNIX.
MM_NOASK
If MM_NOASK is set to "1", metamail will never ask
the user for confirmation before running an
interpreter. Otherwise, MM_NOASK may be set to a
comma-separated list of type names (without white
space) for which the user does not desire
confirmation. Thus, setting MM_NOASK to
"magicmail,audio" will cause the user not to be
asked before running interpreters for magicmail- or
audio-format mail, but the user will still be asked
for all other types. (If the -d command line option
is given, MM_NOASK is set to
1 for spawned processes, allowing -d to work
recursively.)
KEYHEADS
The KEYHEADS variable may be set to a colon-
separated list of header names, which are the only
headers that metamail will print out. By default,
the behavior is as if KEYHEADS were set to:
Date:From:Subject:To:CC:Content-Description
If KEYHEADS is set to the empty string, no header
are printed out. If it is set to an asterisk ("*"),
all headers are printed out. KEYIGNHEADS The
KEYIGNHEADS variable may be set to a colon-separated
list of header names, which are the headers that
metamail will not print out. This variable is only
examined if KEYHEADS is not set.
If KEYIGNHEADS is set to the empty string, all
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headers are printed out. If it is set to an
asterisk ("*"), no headers will be printed out.
MM_NOTTTY
If MM_NOTTTY is set to any nonzero value, metamail
will assume that it is not running in a terminal
window. MM_NOTTTY implies setting MM_NOASK to 1.
If -z is given, MM_NOTTTY is set for spawned
processes, allowing -z to work recursively.
MAILCAPS
This variable can be used to override the default
path search for mailcap files.
METAMAIL_PAGER
If set, this variable overrides "more" as the name
of the program to run to paginate output from an
interpreter, when pagination has been requested.
Note that the normal "PAGER" variable is not used
because many pagers (notably the "less" pager)
interfere with the workings of termcap-based mail
viewers.
NOMETAMAIL
This variable is not actually used by metamail, but
is used by most metamail-compatible mail reading
interfaces. If NOMETAMAIL is set to any value, most
mail reading interfaces will never call the metamail
program, effectively inhibiting all multimedia
functionality.
MM_DEBUG
If MM_DEBUG is set to any value, metamail will
produce slightly more verbose output to tell what it
is doing.
MM_QUIET
If this variable is set to "1", metamail will
produce even less output than usual. In particular,
it will suppress the "Executing..." line unless
MM_DEBUG is set.
Otherwise, this variable can be set to a comma-
separated list of short commands, and the
"Executing..." line will be suppressed for those
commands only.
The default setting for MM_QUIET is "cat", which
means that the "Executing..." line is printed for
all commands executed except "cat". This makes text
support look more natural without sacrificing an
understanding of what is going on in more complex
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circumstances.
MM_YANKMODE
Setting this variable to a non-zero value has the
same effect as the -y switch. Be sure to read the
caveats attached to the description of -y before you
use it. Basically, the only time you would set
MM_YANKMODE is in order to re-enter a mail reader in
which you can't control the way metamail is called,
just to read a single rejected MIME message that was
rejected by a mail agent that does not understand
MIME. In such cases, you should read that message,
exit, and unset this variable.
MM_TRANSPARENT
If this variable is set, metamail will reproduce the
entire raw message on stdout, and will open up a new
terminal emulator window in which to do something
more intelligent. This option supports certain
brain-dead mail readers, such as mailtool, that
actually depend on the output of the UNIX "Mail"
program being the same as the raw message in the
database.
MM_CHARSET
If this variable is set, it will suppress the
printing of character set declarations when mail
headers being printed contain text in this character
set. For example, if you set MM_CHARSET to "iso-
8859-8", it will suppress warnings when header
output is produced in that character set.
DISPLAY Used to create a terminal window under the X11
window system.
WINDOW_PARENT
Used to create a terminal window under the SunTools
window system.
WMHOST Used to create a terminal window under the old
Andrew WM window system.
INTERPRETER ENVIRONMENT
When metamail calls an interpreter specified in a mailcap
file, it sets several environment variables which can be
used by the interpreter if desired:
MM_HEADERS
This variable is set to the full set of RFC822
headers, if any.
MM_MAILER
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This variable is set to the name of the mailer that
called metamail, if the -m option was used.
MM_CONTENTTYPE
This variable is set to the content type, as named
by the Content-type header or passed in via the -c
option. If the content-type has a subtype and
parameters, these are also included in
MM_CONTENTTYPE, e.g. "multipart/mixed;
boundary=foobar".
MM_SUMMARY
This variable is set to an efficient one-line
"caption" of the message, typically including its
sender and subject.
MM_USEPAGER
This variable is set to a non-zero if the use of a
pager has been requested for long output (e.g. the
-p switch was given.) If -p is given, MM_USEPAGER
is set for spawned processes, allowing -p to work
recursively. This option cannot be used with -B.
TERMINAL_CMD
This variable may be set to a string that is used to
start a new terminal window if necessary. The
command to be executed in that window will be
APPENDED to this command. By default, this is set
to something like "xterm -e" if DISPLAY is set, or
"shelltool" if WINDOW_PARENT is set. Users of Sun's
OpenWindows may wish to set TERMINAL_CMD to
"shelltool" if they prefer shelltool over xterm.
MM_RUNASROOT
If set to a non-zero variable, this will allow the
metamail program to be run by root, the same effect
as the "-r" switch to metamail.
FILES
$HOME/.mailcap:/etc/mailcap:/usr/etc/mailcap:/usr/local/etc/mailcap
-- default path for mailcap files.
SEE ALSO
audiocompose(1), audiosend(1), ezview(1), getfilename(1),
mailto-hebrew(1), mailto(1), metasend(1), mmencode(1),
richtext(1), showaudio(1), showexternal(1), shownonascii(1),
showpartial(1), showpicture(1), mailcap(4)
BUGS
In a multipart/alternative body or body parts, some headers
in the embedded part that should be displayed may not be
displayed. This will rarely be a problem. Also, in a
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multipart/alternative, anything of type "multipart" or
"message" is considered to be a recognized part, regardless
of the recognizability of its contents. This might be a
problem, only further experience will tell.
The "textualnewlines" field in mailcap entries affects a
global table of exceptions. This means that if there is
more than one mailcap entry for a given content-type, and
they have conflicting "textualnewlines" settings, the wrong
value may be used. I have been unable to conceive of a
situation where this would be a real problem, because it
seems inconceivable that a single content-type would ever
require newlines to be treated in two different ways,
regardless of the environment.
The "%n" and "%F" mailcap fields do not work in "test"
clauses, because metamail does not perform sufficient
lookahead to do this right.
COPYRIGHT
Copyright (c) 1991 Bell Communications Research, Inc.
(Bellcore)
Permission to use, copy, modify, and distribute this
material for any purpose and without fee is hereby granted,
provided that the above copyright notice and this permission
notice appear in all copies, and that the name of Bellcore
not be used in advertising or publicity pertaining to this
material without the specific, prior written permission of
an authorized representative of Bellcore. BELLCORE MAKES NO
REPRESENTATIONS ABOUT THE ACCURACY OR SUITABILITY OF THIS
MATERIAL FOR ANY PURPOSE. IT IS PROVIDED "AS IS", WITHOUT
ANY EXPRESS OR IMPLIED WARRANTIES.
AUTHOR
Nathaniel S. Borenstein
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