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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 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  existing
       (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 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.

SEE ALSO

       run-mailcap(1), mailcap.order(5), update-mime(8)

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.

AUTHOR

       Nathaniel S. Borenstein