MAILCAP(5)                    File Formats Manual                   MAILCAP(5)

       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 vo-
       luminous,  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.  "im-

       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 re-
       placed 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  Con-
       tent-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  it-

       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 re-
       placed 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 sec-
       ond 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 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-
       mation, and to apply any necessary Content-Transfer-Encoding.   Concep-
       tually, "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 win-
               dow-oriented  mail reader under X11) this will require the cre-
               ation of a new terminal emulation window, while in  most  envi-
               ronments  it  will  not.  If the mailcap entry specifies "need-
               sterminal" and metamail is not running on a terminal (as deter-
               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.

       cap -- default path for mailcap files.

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

       RFC 1524 (<>)

       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

Bellcore Prototype                 Release 2                        MAILCAP(5)
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