METAMAIL(1)METAMAIL(1)NAMEmetamail - 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. Meta‐
mail 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 meta‐
mail. The latter may ignore the command line syntax, and need only be
concerned with the mailcap file syntax, as described in a later sec‐
tion.
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 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 run‐
ning 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 con‐
tent-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.
-E <contentencoding>
This option tells metamail to use the specified content trans‐
fer encoding rather than the one in the headers, if any.
-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 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 interac‐
tive rather than requiring pagination. Metamail can tell
whether or not to use a pager 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 meta‐
mail 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 KEY‐
HEADS 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/bin/reset should be exe‐
cuted to reset the terminal state, before any other I/O activ‐
ity.
-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 avail‐
able to any 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 head‐
ers, 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 mes‐
sage 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 fin‐
ished. 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 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.
The format of mailcap files is explained in the manual entry for mail‐
cap(5).
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 con‐
firmation. 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 head‐
ers 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 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 pro‐
gram to run to paginate output from an interpreter, when pagi‐
nation has been requested. Note that the normal "PAGER" vari‐
able 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 NOMETA‐
MAIL 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 "Exe‐
cuting..." 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 sup‐
pressed 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 sac‐
rificing an understanding of what is going on in more complex
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 char‐
acter 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 sys‐
tem.
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 Con‐
tent-type header or passed in via the -c option. If the con‐
tent-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 OpenWin‐
dows 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 ALSOaudiocompose(1), audiosend(1), ezview(1), getfilename(1), mailto-
hebrew(1), mailto(1), metasend(1), mimencode(1), richtext(1), showau‐
dio(1), showexternal(1), shownonascii(1), showpartial(1), showpic‐
ture(1), mailcap(5)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 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 per‐
taining to this material without the specific, prior written permission
of an authorized representative of Bellcore. BELLCORE MAKES NO REPRE‐
SENTATIONS ABOUT THE ACCURACY OR SUITABILITY OF THIS MATERIAL FOR ANY
PURPOSE. IT IS PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED WAR‐
RANTIES.
AUTHOR
Nathaniel S. Borenstein
Bellcore Prototype Release 2 METAMAIL(1)
