Computer Science
METAMAIL(1) METAMAIL(1)
NAME
metamail - infrastructure for mailcap-based multimedia
mail handling
SYNOPSIS
metamail[-b] [-B] [-c contenttype ...] [-d] [-e] [-E con-
tentencoding] [-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 mod-
ified 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 automati-
cally by the user's mail reading program, whenever a non-
text message is to be viewed. This manual page, there-
fore, 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 con-
cerned with the command line syntax of metamail. The lat-
ter 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 for-
mat, 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 new-
lines for textual data, but not for other data, unless
instructed otherwise by a "textualnewlines" field in a
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 "needstermi-
nal" 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 ques-
tions 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 envi-
ronment 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 new-
lines 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
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 environ-
ment variable METAMAIL_PAGER can be used to spec-
ify an alternative command to use. Note that one
should use -p rather than piping the output of
metamail through a pager, because some inter-
preters called by metamail might be interactive
rather than requiring pagination. Metamail can
tell whether or not to use a pager from informa-
tion 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 meta-
mail 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 inter-
preter, 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 mes-
sage. By default, this information is obtained
from the headers. This information will be placed
in the environment to make it available to any
interpreters called by metamail.
-w This option tells metamail that instead of con-
sulting 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 vari-
able.) 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
**** 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 pro-
grams 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 pro-
gram to run in order to show the user mail in a given for-
mat. 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/mail-
cap:/etc/mailcap:/etc/mail/mailcap:/usr/public/lib/mail-
cap"
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.
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 inter-
preter. Otherwise, MM_NOASK may be set to a
comma-separated list of type names (without white
space) for which the user does not desire confir-
mation. Thus, setting MM_NOASK to "magic-
mail,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 recur-
sively.)
KEYHEADS
The KEYHEADS variable may be set to a colon-sepa-
rated 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
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 pro-
cesses, 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 read-
ing 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 pro-
duce 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 "Execut-
ing..." 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 com-
plex 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 charac-
ter 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 Sun-
Tools 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
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_CONTENT-
TYPE, 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/mail-
cap:/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), mail-
cap(4)
BUGS
In a multipart/alternative body or body parts, some head-
ers in the embedded part that should be displayed may not
be displayed. This will rarely be a problem. Also, in a
multipart/alternative, anything of type "multipart" or
"message" is considered to be a recognized part, regard-
less 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 mate-
rial for any purpose and without fee is hereby granted,
provided that the above copyright notice and this permis-
sion notice appear in all copies, and that the name of
Bellcore not be used in advertising or publicity pertain-
ing 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 PRO-
VIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES.
AUTHOR
Nathaniel S. Borenstein
Bellcore Prototype Release 2 1
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