.TH MAILCAP 4 "Release 2" "Bellcore Prototype"
.SH NAME
mailcap - metamail capabilities file
.SH DESCRIPTION
The
.I mailcap
file is read by the
.I metamail
program to determine how to display non-text at the local site.

The syntax of a mailcap file is quite simple, at least compared to termcap
files.  Any line that starts with "#" is a comment.  Blank lines are
ignored.  Otherwise, each line defines a single mailcap entry for a single
content type.  Long lines may be con tinued by ending them with a backslash
character, \\.

Each individual mailcap entry consists of a content-type specification, a
command to execute, and (possibly) a set of optional "flag" values.  For
example, a very simple mailcap entry (which is actually a built-in default
behavior for metamail) would look like this:

text/plain; cat %s

The optional flags can be used to specify additional information about the
mail-handling command.  For example:

text/plain; cat %s; copiousoutput

can be used to indicate that the output of the 'cat' command may be
voluminous, requiring either a scrolling window, a pager, or some other
appropriate coping mechanism.

The "type" field (text/plain, in the above example) is simply any legal
content type name, as defined by RFC 822.  In practice, this is almost any
string.  It is the string that will be matched against the "Content-type"
header (or the value passed in wit h -c) to decide if this is the mailcap
entry that matches the current message.  Additionally, the type field may
specify a subtype (e.g.  "text/ISO-8859-1") or a wildcard to match all
subtypes (e.g.  "image/*").

The "command" field is any UNIX command ("cat %s" in the above example), and
is used to specify the interpreter for the given type of message.  It will
be passed to the shell via the system(3) facility.  Semicolons and
backslashes within the command must be quoted with backslashes.  If the
command contains "%s", those two characters will be replaced by the name of
a file that contains the body of the message.  If it contains "%t', those
two characters will be replaced by the content-type field, including t he
subtype, if any.  (That is, if the content-type was "image/pbm;
opt1=something-else", then "%t" would be replaced by "image/pbm".)  If the
command field contains "%{" followed by a parameter name and a closing "}",
then all those characters will be r eplaced by the value of the named
parameter, if any, from the Content-type header.  Thus, in the previous
example, "%{opt1}" will be replaced by "something-else".  Finally, if the
command contains "\%", those two characters will be replaced by a single %
ch



aracter.  (In fact, the backslash can be used to quote any character,
including itself.)

If no "%s" appears in the command field, then instead of placing the message
body in a temporary file, metamail will pass the body to the command on the
standard input.  This is helpful in saving /tmp file space, but can be
problematic for window-oriented applications under some window systems such
as MGR.

Two special codes can appear in the viewing command for objects of type
multipart (any subtype).  These are "%n" and "%F".  %n will be replaced by
the number of parts within the multipart object.  %F will be replaced by a
series of arguments, two for each part, giving first the content-type and
then the name of the temporary file where the decoded part has been stored.
In addition, for each file created by %F, a second file is created, with the
same name followed by "H", which contains the header informa tion for that
body part.  This will not be needed by most multipart handlers, but it is
there if you ever need it.

The "notes=xxx" field is an uninterpreted string that is used to specify the
name of the person who installed this entry in the mailcap file.  (The "xxx"
may be replaced by any text string.)

The "test=xxx" field is a command that is executed to determine whether or
not the mailcap line actually applies.  That is, if the content-type field
matches the content-type on the message, but a "test=" field is present,
then the test must succeed befor e the mailcap line is considered to "match"
the message being viewed.  The command may be any UNIX command, using the
same syntax and the same %-escapes as for the viewing command, as described
above.  A command is considered to succeed if it exits with a zero exit
status, and to fail otherwise.

The "print=xxx" field is a command that is executed to print the data
instead of display it interactively.  This behavior is usually a consequence
of invoking metamail with the "-h" switch.

The "textualnewlines" field can be used in the rather obscure case where
metamail's default rules for treating newlines in base64-encoded data are
unsatisfactory.  By default, metamail will translate CRLF to the local
newline character in decoded base64 o utput if the content-type is "text"
(any subtype), but will not do so otherwise.  A mailcap entry with a field
of "textualnewlines=1" will force such translation for the specified
content-type, while "textualnewlines=0" will guarantee that the translation
does not take place even for textual content-types.

The "compose" field may be used to specify a program that can be used to
compose a new body or body part in the given format.  Its intended use is to
support mail composing agents that support the composition of multiple types
of mail using external compo sing agents.  As with the view-command, the
compose command will be executed after replacing certain escape sequences
starting with "%".  In particular, %s should be replaced by the name of a
file to which the composed data is to be written by the specifie d composing
program, thus allowing th3e calling program (e.g.  metamail) to tell the
called program where to store the composed data.  If %s does not appear,
then the composed data will be assumed to be written by the composing
programs to standard output.  The result of the composing program may be
data that is NOT yet suitable for mail transport -- that is, a
Content-Transfer-Encoding may still need to be applied to the data.

The "composetyped" field is similar to the "compose" field, but is to be
used when the composing program needs to specify the Content-type header
field to be applied to the composed data.  The "compose" field is simpler,
and is preferred for use with exis ting (non-mail-oriented) programs for
composing data in a given format.  The "composetyped" field is necessary
when the Content-type information must include auxilliary parameters, and
the composition program must then know enough about mail formats to pr oduce
output that includes the mail type information, and to apply any necessary
Content-Transfer-Encoding.  Conceptually, "compose" specifies a program that
simply outputs the specified type of data in its raw form, while
"composetyped" specifies a prog ram that outputs the data as a MIME object,
with all necessary Content-* headers already in place.

.TP 8
.B needsterminal
If this flag is given, the named interpreter needs to interact with the user
on a terminal.  In some environments (e.g.  a window-oriented mail reader
under X11) this will require the creation of a new terminal emulation
window, while in most environments it will not.  If the mailcap entry
specifies "needsterminal" and metamail is not running on a terminal (as
determined by isatty(3), the -x option, and the MM_NOTTTY environment
variable) then metamail will try to run the command in a new terminal
emulatio n window.  Currently, metamail knows how to create new windows
under the X11, SunTools, and WM window systems.
.TP 8
.B copiousoutput
This flag should be given whenever the interpreter is capable of producing
more than a few lines of output on stdout, and does no interaction with the
user.  If the mailcap entry specifies copiousoutput, and pagination has been
requested via the "-p" comm and, then the output of the command being
executed will be piped through a pagination program ("more" by default, but
this can be overridden with the METAMAIL_PAGER environment variable).
.SH BUILT-IN CONTENT-TYPE SUPPORT
The metamail program has built-in support for a few key content-types.  In
particular, it supports the text type, the multipart and
multipart/alternative type, and the message/rfc822 types.  This support is
incomplete for many subtypes -- for example, it only supports US-ASCII text
in general.  This kind of built-in support can be OVERRIDDEN by an entry in
any mailcap file on the user's search path.  Metamail also has rudimentary
built-in support for types that are totally unrecognized -- i.e.  for which
n o mailcap entry or built-in handler exists.  For such unrecognized types,
metamail will write a file with a "clean" copy of the data -- i.e.  a copy
in which all mail headers have been removed, and in which any 7-bit
transport encoding has been decoded.
.SH FILES
$HOME/.mailcap:/etc/mailcap:/usr/etc/mailcap:/usr/local/etc/mailcap --
default path for mailcap files.
.SH SEE ALSO
metamail(1)
.SH 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.
.SH AUTHOR
Nathaniel S. Borenstein
