Ubuntu Manpage: mailcap - metamail capabilities file

Provided by: mailcap_3.70+nmu1ubuntu1_all

NAME

       mailcap - metamail capabilities file

DESCRIPTION

The mailcap file is read by the 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 continued 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
informational RFC 1524. 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 with -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 the
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 replaced 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 % character.
(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 information 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 before 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 output 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 composing 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 specified composing
program, thus allowing the 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 existing (non-mail-oriented) programs for composing data in a
given format. The "composetyped" field is necessary when the Content-type information must include
auxiliary parameters, and the composition program must then know enough about mail formats to produce
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 program that outputs the data as a MIME object, with all necessary
Content-* headers already in place.

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 emulation window. Currently, metamail knows how to create new windows under
the X11, SunTools, and WM window systems.

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" command, 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).

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 no
       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.

FILES

       $HOME/.mailcap:/etc/mailcap:/usr/share/etc/mailcap:/usr/local/etc/mailcap --  default  path  for  mailcap
       files.

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.

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