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metamail (1)
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    NAME
         metamail - infrastructure for mailcap-based multimedia  mail
         handling
    
    SYNOPSIS
         metamail[-b] [-B] [-c contenttype ...] [-d] [-e] [-E conten-
         tencoding]  [-f   from-name] [-h] [-m mailer-name] [-p] [-P]
         [-r] [-s subject] [-q] [-w] [-x] [-y] [-z] [file-name]
    
    DESCRIPTION
         The metamail program reads a "mailcap" file to determine how
         to  display  non-text at the local site.  Every mail-reading
         interface needs to call metamail whenever non-text  mail  is
         being  viewed,  unless the mail is of a type that is already
         understood by the mail-reading  program.  Metamail  consults
         the mailcap file(s) to determine what program to use to show
         the message to the user.
    
         At a site where all mail reading interfaces have been  modi-
         fied to call metamail for non-text mail, extending the local
         email system to handle a new media type in the mail  becomes
         a  simple  matter  of  adding  a  line  to  a  mailcap file.
         (Although this manual page will discuss only mail,  metamail
         is  equally  useful in adding multimedia support to news and
         bulletin board reading  programs,  assuming  those  programs
         preserve  the "Content-type" header or some other indication
         of the content type of the messages.)
    
         In  general,  users  will  never  run   metamail   directly.
         Instead, metamail will be invoked for the user automatically
         by the user's mail reading program, whenever a non-text mes-
         sage  is  to  be  viewed.   This  manual page, therefore, is
         directed not at end users, but at two categories of readers:
         those  who are adding metamail support to a particular mail-
         reading program, and those who are adding lines to a mailcap
         file.  The former need only to be concerned with the command
         line syntax of metamail.  The latter may ignore the  command
         line  syntax,  and  need  only be concerned with the mailcap
         file syntax, as described in a later section.
    
         Note:  Metamail determines the type of a message  using  the
         "Content-type"  header,  as defined in RFC 1049 and RFC-1341
         (MIME).  However, using the -b and -c options, metamail  can
         be  made  to  work with mail that is not in Internet format,
         including X.400 messages.  Note also that metamail automati-
         cally decodes mail that has been encoded for 7 bit transport
         if the mail includes a Content-Transfer-Encoding  header  as
         specified  by  RFC-1341.   If  data has been encoded via the
         "base64" encoding, it will map CRLF to  local  newlines  for
         textual data, but not for other data, unless instructed oth-
         erwise by a "textualnewlines" field in a mailcap entry.
    
    OPTIONS
         When called with no options or arguments,  metamail  expects
         to  receive an RFC 822 format message on its standard input.
         The following options can alter that expectation:
    
         -b      This option tells metamail that the message  is  not
                 in  RFC  822 format, but instead is only the body of
                 the message (i.e. there  are  no  message  headers).
                 The use of -b requires the use of -c.
    
         -B      This option tells metamail that the message is to be
                 displayed   in   the   background,  if  it  is  non-
                 interactive (i.e. it doesn't have  the  "needstermi-
                 nal"  attribute  in the mailcap file).  It cannot be
                 used with -p or -P.
    
         -c <contenttype>
                 This option tells metamail to use the specified con-
                 tent  type  rather  than  the one in the headers, if
                 any.
    
         -d      This option tells metamail not to ask any  questions
                 before  running  an interpreter to view the message.
                 (By default, metamail  always  asks  before  running
                 almost  any  interpreter,  if  it  is  running in an
                 interactive terminal and  the  MM_NOASK  environment
                 variable is not set.  However, it does not ask about
                 the content-type "text"  --  that  is,  the  default
                 value for MM_NOASK is "text,text/us-ascii")
    
         -e      This option tells metamail to "eat" leading newlines
                 in  message bodies.  This is particularly useful for
                 MH-format mail.
    
         -f <address>
                 This option specifies the name of the sender of  the
                 message.   Otherwise,  this  is  determined from the
                 header,  if  possible.   This  information  will  be
                 placed  in  the  environment to make it available to
                 any interpreters called by metamail.
    
         -h      This option specifies that metamail  is  being  used
                 for  printing  a message.  In particular, this means
                 that the normal mailcap "command" field will not  be
                 executed,  but  instead the command specified in the
                 "print" field will be executed.  (If there is  noth-
                 ing  in  the  print field, the mailcap entry will be
                 ignored and the search will continue for a  matching
                 mailcap entry that does have a print field.)  The -h
                 option automatically turns on the -d option.
    
         -m <mailername>
                 This option specifies the name of the  mail  program
                 that  called  metamail.   This  information  will be
                 placed in the environment to make  it  available  to
                 any interpreters called by metamail.
    
         -p      This option specifies  that,  if  necessary,  output
                 should  be shown to the user one page at a time.  By
                 default, this will cause such  output  to  be  piped
                 through  the  "more"  command,  but  the environment
                 variable METAMAIL_PAGER can be used  to  specify  an
                 alternative  command  to  use.  Note that one should
                 use -p rather than piping  the  output  of  metamail
                 through a pager, because some interpreters called by
                 metamail might be interactive rather than  requiring
                 pagination.  Metamail can tell whether or not to use
                 a pager from information in the mailcap file.   This
                 option cannot be used with -B.
    
         -P      This option is just like -p,  except  that  it  also
                 causes metamail to print "Press RETURN to go on" and
                 await a RETURN after it has finished with  the  mes-
                 sage.   This  is intended for use only when metamail
                 calls itself recursively in a  new  terminal  window
                 created  only  for that purpose.  This option cannot
                 be used with -B.
    
         -q      This option tells metamail to be quiet.  By default,
                 metamail prints a few key message headers (controll-
                 able with the KEYHEADS and  KEYIGNHEADS  environment
                 variables)  and  some other informative information,
                 on stdout before running the interpreter,  but  this
                 behavior is suppressed with -q.
    
         -r      This option specifies that it is OK to run as  root.
                 By  default,  metamail refuses to run if the real or
                 effective user id is root.  You  can  get  the  same
                 effect using the MM_RUNASROOT environment variable.
    
         -R      This option specifies that the /usr/ucb/reset should
                 be  executed to reset the terminal state, before any
                 other I/O activity.
    
         -s <subject>
                 This option specifies the subject of the  mail  mes-
                 sage.  By default, this information is obtained from
                 the headers.  This information will be placed in the
                 environment to make it available to any interpreters
                 called by metamail.
    
         -w      This option tells metamail that instead of  consult-
                 ing  a  mailcap  file  to  decide how to display the
                 data, it should simply decode each part and write it
                 to  a  file  in  its  raw  (possibly binary) format.
                 Depending  on  the  circumstances  in  which  it  is
                 called,  metamail  may  derive  the file name to use
                 from the message headers, by asking the user, or  by
                 generating a unique temporary file name.
    
         -x      This option tells metamail that it is definitely not
                 running on a terminal, no matter what isatty() says.
                 This is necessary when metamail is actually  running
                 on  a  pseudoterminal and isatty(3) returns TRUE but
                 there's really no terminal on which to interact with
                 the  user.   The  same  effect  as  -x  can  also be
                 obtained with the environment variable MM_NOTTTY.
    
         -y      This option tells metamail to try to "yank" a  MIME-
                 format  message from the body of the message.  It is
                 useful when a MIME-format has  been  rejected  by  a
                 mail delivery system that does not now how to format
                 the rejection in a MIME-compliant manner.  (For  the
                 convenience  of those who can't control how metamail
                 is called from their mail reader, this can  also  be
                 set with the MM_YANKMODE variable.)  If you use yank
                 mode on messages that really ARE in MIME format,  or
                 on  messages  that  do not contain a MIME message in
                 the body, the effects could  be  VERY  strange.   It
                 won't hurt you, but you won't see anything very use-
                 ful, either.
    
         -z      This option tells metamail to delete its input  file
                 when  finished.   The -z option requires that a file
                 name was given as an argument to metamail, i.e. that
                 it is not reading stdin.
    
         -T      This option is  intended  to  be  used  by  metamail
                 recursively,   to   turn   off  the  effect  of  the
                 MM_TRANSPARENT environment variable.  It should only
                 be used when the metamail program restarts itself in
                 a terminal emulator window.
    
         File Name Arguments
                 Any argument that does not start with "-" is  inter-
                 preted  as  the  name  of  a file to read instead of
                 standard input.
    
    UNRECOGNIZED MAIL TYPES
         From time to time, metamail may tell you something like
    
         **** Unrecognized mail type: 'smell-o-vision'.   Writing  to
         file /tmp/metamail.1234 ****
    
         What this means is that your are trying to  read  a  message
         that  contains  data  that  is  marked as being in "smell-o-
         vision" format, but that your site has  not  yet  configured
         metamail to properly display that type of data.  In the gen-
         eral case, such  configuration  is  accomplished  using  the
         mailcap file mechanism, as described in the next section.
    
         For unrecognized types, metamail simply removes  all  header
         and encoding information from the data, and writes it out to
         a temporary file.  (If running interactively, it  will  give
         you  more  alternatives  --  writing it to a temporary file,
         viewing it as text, or jus skipping it.)  It is  up  to  the
         user  to  delete  such  files when he or she is through with
         them.
    
    
    THE MAILCAP FILE(S)
         The primary purpose of the  metamail  program  is  to  allow
         diverse  mail reading programs to centralize their access to
         multimedia information.  If all the  mail  reading  programs
         call  a  single  program  to handle non-text mail, then only
         that program needs to know about the diverse types  of  non-
         text mail that might be received.
    
         The metamail program is made  more  flexible  in  this  role
         through  the  mechanism of one or more "mailcap" files.  The
         purpose of the mailcap files is to tell metamail  what  pro-
         gram  to  run in order to show the user mail in a given for-
         mat.  Thus it becomes possible to add a new  media  type  to
         all  of the mail reading programs at a site simply by adding
         a line to a mailcap file.
    
         Metamail uses a search path to find the mailcap  file(s)  to
         consult.   Unlike  many path searches, if necessary metamail
         will read all the mailcap files on its path.   That  is,  it
         will  keep  reading mailcap files until it runs out of them,
         or until it finds a line that tells it  how  to  handle  the
         piece  of  mail  it  is  looking at.  If it finds a matching
         line, it will execute the command that is specified  in  the
         mailcap file.
    
         The default search path is equivalent to
    
         $HOME/.mailcap:/usr/local/etc/mailcap:/usr/etc/mailcap:/etc/mailcap:/etc/mail/mailcap:/usr/public/lib/mailcap"
    
         It  can  be  overridden  by setting the MAILCAPS environment
         variable.   Note:  Metamail  does  not  actually   interpret
         environment  variables  such  as  $HOME or the "~" syntax in
         this path search.
    
         The format of mailcap files is explained in the manual entry
         for mailcap(4).
    
    
    NON-ASCII HEADER FIELDS
         Metamail has rudimentary built-in support for  the  emerging
         Internet standards for non-ASCII data in mail headers.  What
         this means is that such data will  be  recognized,  decoded,
         and sent to the terminal.  This behavior may be more or less
         reasonable, depending on the character  set  in  the  header
         data  and the capability of the user's terminal, but it will
         rarely be any worse than showing such data  in  its  encoded
         form.
    
    ENVIRONMENT
         METAMAIL_TMPDIR
                 If set, this variable overrides "/tmp" as  the  name
                 of  the  directory  in which metamail and associated
                 programs will create temporary files on UNIX.
    
         MM_NOASK
                 If MM_NOASK is set to "1", metamail will  never  ask
                 the  user  for confirmation before running an inter-
                 preter.  Otherwise, MM_NOASK may be set to a  comma-
                 separated  list  of type names (without white space)
                 for which the user  does  not  desire  confirmation.
                 Thus,  setting  MM_NOASK  to  "magicmail,audio" will
                 cause the user not to be asked before running inter-
                 preters for magicmail- or audio-format mail, but the
                 user will still be asked for all other  types.   (If
                 the -d command line option is given, MM_NOASK is set
                 to 1 for spawned  processes,  allowing  -d  to  work
                 recursively.)
    
         KEYHEADS
                 The  KEYHEADS  variable  may  be  set  to  a  colon-
                 separated  list  of header names, which are the only
                 headers that metamail will print out.   By  default,
                 the behavior is as if KEYHEADS were set to:
    
                 Date:From:Subject:To:CC:Content-Description
    
                 If KEYHEADS is set to the empty  string,  no  header
                 are printed out.  If it is set to an asterisk ("*"),
                 all  headers  are  printed  out.   KEYIGNHEADS   The
                 KEYIGNHEADS variable may be set to a colon-separated
                 list of header names, which  are  the  headers  that
                 metamail  will  not print out. This variable is only
                 examined if KEYHEADS is not set.
    
                 If KEYIGNHEADS is  set  to  the  empty  string,  all
                 headers  are printed out.  If it is set to an aster-
                 isk ("*"), no headers will be printed out.
    
         MM_NOTTTY
                 If MM_NOTTTY is set to any nonzero  value,  metamail
                 will  assume  that  it  is not running in a terminal
                 window.  MM_NOTTTY implies setting  MM_NOASK  to  1.
                 If  -z  is  given,  MM_NOTTTY  is  set  for  spawned
                 processes, allowing -z to work recursively.
    
         MAILCAPS
                 This variable can be used to  override  the  default
                 path search for mailcap files.
    
         METAMAIL_PAGER
                 If set, this variable overrides "more" as  the  name
                 of  the  program  to  run to paginate output from an
                 interpreter, when  pagination  has  been  requested.
                 Note  that  the  normal "PAGER" variable is not used
                 because  many  pagers  (notably  the  "less"  pager)
                 interfere  with  the  workings of termcap-based mail
                 viewers.
    
         NOMETAMAIL
                 This variable is not actually used by metamail,  but
                 is  used  by  most  metamail-compatible mail reading
                 interfaces.  If NOMETAMAIL is set to any value, most
                 mail reading interfaces will never call the metamail
                 program, effectively inhibiting all multimedia func-
                 tionality.
    
         MM_DEBUG
                 If MM_DEBUG is set to any value, metamail will  pro-
                 duce slightly more verbose output to tell what it is
                 doing.
    
         MM_QUIET
                 If this variable is set to "1", metamail  will  pro-
                 duce even less output than usual.  In particular, it
                 will  suppress  the   "Executing..."   line   unless
                 MM_DEBUG is set.
    
                 Otherwise, this variable can  be  set  to  a  comma-
                 separated  list  of short commands, and the "Execut-
                 ing..." line will be suppressed for  those  commands
                 only.
    
                 The default setting for  MM_QUIET  is  "cat",  which
                 means  that  the  "Executing..." line is printed for
                 all commands executed except "cat".  This makes text
                 support  look  more  natural  without sacrificing an
                 understanding of what is going on  in  more  complex
                 circumstances.
    
         MM_YANKMODE
                 Setting this variable to a non-zero  value  has  the
                 same   effect as the -y switch.  Be sure to read the
                 caveats attached to the description of -y before you
                 use  it.  Basically,  the  only  time  you would set
                 MM_YANKMODE is in order to re-enter a mail reader in
                 which  you can't control the way metamail is called,
                 just to read a single rejected MIME message that was
                 rejected  by  a  mail agent that does not understand
                 MIME.  In such cases, you should read that  message,
                 exit, and unset this variable.
    
         MM_TRANSPARENT
                 If this variable is set, metamail will reproduce the
                 entire raw message on stdout, and will open up a new
                 terminal emulator window in which  to  do  something
                 more  intelligent.   This  option  supports  certain
                 brain-dead mail  readers,  such  as  mailtool,  that
                 actually  depend  on  the  output of the UNIX "Mail"
                 program being the same as the  raw  message  in  the
                 database.
    
         MM_CHARSET
                 If this variable is set, it will suppress the print-
                 ing  of character set declarations when mail headers
                 being printed contain text in  this  character  set.
                 For  example, if you set MM_CHARSET to "iso-8859-8",
                 it will suppress warnings when header output is pro-
                 duced in that character set.
    
         DISPLAY Used to create a terminal window under the X11  win-
                 dow system.
    
         WINDOW_PARENT
                 Used to create a terminal window under the  SunTools
                 window system.
    
         WMHOST  Used to create  a  terminal  window  under  the  old
                 Andrew WM window system.
    
    INTERPRETER ENVIRONMENT
         When metamail calls an interpreter specified  in  a  mailcap
         file,  it  sets  several  environment variables which can be
         used by the interpreter if desired:
    
         MM_HEADERS
                 This variable is set  to  the  full  set  of  RFC822
                 headers, if any.
    
         MM_MAILER
                 This variable is set to the name of the mailer  that
                 called metamail, if the -m option was used.
    
         MM_CONTENTTYPE
                 This variable is set to the content type,  as  named
                 by  the  Content-type header or passed in via the -c
                 option.  If  the  content-type  has  a  subtype  and
                 parameters,    these    are    also    included   in
                 MM_CONTENTTYPE,        e.g.        "multipart/mixed;
                 boundary=foobar".
    
         MM_SUMMARY
                 This variable is set to an efficient one-line  "cap-
                 tion" of the message, typically including its sender
                 and subject.
    
         MM_USEPAGER
                 This variable is set to a non-zero if the use  of  a
                 pager  has  been requested for long output (e.g. the
                 -p switch was given.)  If -p is  given,  MM_USEPAGER
                 is  set  for  spawned processes, allowing -p to work
                 recursively.  This option cannot be used with -B.
    
         TERMINAL_CMD
                 This variable may be set to a string that is used to
                 start  a new terminal window if necessary.  The com-
                 mand to be executed in that window will be  APPENDED
                 to  this  command.  By default, this is set to some-
                 thing   like  "xterm  -e"  if  DISPLAY  is  set,  or
                 "shelltool" if WINDOW_PARENT is set.  Users of Sun's
                 OpenWindows  may  wish  to   set   TERMINAL_CMD   to
                 "shelltool" if they prefer shelltool over xterm.
    
         MM_RUNASROOT
                 If set to a non-zero variable, this will  allow  the
                 metamail  program to be run by root, the same effect
                 as the "-r" switch to metamail.
    
    FILES
         $HOME/.mailcap:/etc/mailcap:/usr/etc/mailcap:/usr/local/etc/mailcap
         -- default path for mailcap files.
    
    SEE ALSO
         audiocompose(1),  audiosend(1),  ezview(1),  getfilename(1),
         mailto-hebrew(1),   mailto(1),   metasend(1),   mmencode(1),
         richtext(1), showaudio(1), showexternal(1), shownonascii(1),
         showpartial(1), showpicture(1), mailcap(4)
    
    BUGS
         In a multipart/alternative body or body parts, some  headers
         in  the  embedded  part  that should be displayed may not be
         displayed.  This will rarely  be  a  problem.   Also,  in  a
         multipart/alternative, anything of type "multipart" or "mes-
         sage" is considered to be a recognized part,  regardless  of
         the  recognizability of its contents.  This might be a prob-
         lem, only further experience will tell.
    
         The "textualnewlines" field in  mailcap  entries  affects  a
         global  table  of  exceptions.   This means that if there is
         more than one mailcap entry for a  given  content-type,  and
         they  have conflicting "textualnewlines" settings, the wrong
         value may be used.  I have been  unable  to  conceive  of  a
         situation  where  this  would  be a real problem, because it
         seems inconceivable that a single  content-type  would  ever
         require  newlines  to  be  treated  in  two  different ways,
         regardless of the environment.
    
         The "%n" and "%F" mailcap  fields  do  not  work  in  "test"
         clauses, because metamail does not perform sufficient looka-
         head to do this right.
    
    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
    
    
    
    


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