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           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  "Con-
           tent-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  exam-
           ple), and is used to specify the interpreter for the given type of mes-
           sage.  It will be passed to  the  shell  via  the  system(3)  facility.
           Semicolons and backslashes within the command must be quoted with back-
           slashes.  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  con-
           tent-type  field, including the subtype, if any.  (That is, if the con-
           tent-type was "image/pbm;  opt1=something-else",  then  "%t"  would  be
           replaced  by  "image/pbm".)    If the command field contains  "%{" fol-
           lowed 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
           most multipart handlers, but it is there if you ever need it.
           The "notes=xxx" field is an uninterpreted string that is used to  spec-
           ify  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 consid-
           ered to "match" the message being viewed.  The command may be any  UNIX
           command,  using the same syntax and the same %-escapes as for the view-
           ing 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 conse-
           quence 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 guaran-
           tee that the translation does not take place even for textual  content-
           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 cer-
           tain 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  suit-
           able  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 aux-
           iliary parameters, and the composition program must  then  know  enough
           about mail formats to produce output that includes the mail type infor-
                   mined by isatty(3), the -x option, and the  MM_NOTTTY  environ-
                   ment  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
                   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 speci-
                   fies  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  multi-
           part/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.


           $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 per-
           taining to this material without the specific, prior written permission
           of  an authorized representative of Bellcore.  BELLCORE MAKES NO REPRE-


           Nathaniel S. Borenstein

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