MAILCAP(4)                 Kernel Interfaces Manual                 MAILCAP(4)

       mailcap - metamail capabilities file

       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 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 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.

       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

       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.

               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.

               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

       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

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


       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

       Nathaniel S. Borenstein

Bellcore Prototype                 Release 2                        MAILCAP(4)