mhshow - display MIME messages


SYNOPSIS

       mhshow [+folder] [msgs] [-file file]
            [-part number]... [-type content]...
            [-serialonly] [-noserialonly] [-pause] [-nopause]
            [-check] [-nocheck] [-form formfile]
            [-rcache policy] [-wcache policy]
            [-verbose] [-noverbose] [-version] [-help]


DESCRIPTION

       The  mhshow  command  display  contents  of a MIME (multi-
       media) message or collection of messages.

       mhshow manipulates multi-media messages  as  specified  in
       RFC-2045  thru  RFC-2049.   Currently mhshow only supports
       encodings in message bodies,  and  does  not  support  the
       encoding of message headers as specified in RFC-2047.

       By  default  mhshow  will display all parts of a multipart
       message.  By using the `-part' and `-type'  switches,  you
       may limit the scope of mhshow to particular subparts (of a
       multipart content) and/or particular content types.

       The option `-file file' directs mhshow to use  the  speci­
       fied  file  as  the  source message, rather than a message
       from a folder.  If you specify  this  file  as  "-",  then
       mhshow  will  accept  the  source  message on the standard
       input.  Note that the file, or input from  standard  input
       should be a validly formatted message, just like any other
       nmh message.  It should NOT be in  mail  drop  format  (to
       convert a file in mail drop format to a folder of nmh mes­
       sages, see inc (1)).

       A part specification consists of a series of numbers sepa­
       rated  by  dots.  For example, in a multipart content con­
       taining three parts, these would be named as 1, 2, and  3,
       respectively.  If part 2 was also a multipart content con­
       taining two parts, these would be named as  2.1  and  2.2,
       respectively.   Note  that the `-part' switch is effective
       for only messages containing a multipart  content.   If  a
       message  has some other kind of content, or if the part is
       itself another multipart content, the `-part' switch  will
       not prevent the content from being acted upon.

       A  content  specification consists of a content type and a
       subtype.  The initial list of "standard" content types and

       used contents is briefly reproduced here:

            Type         Subtypes
            ----         --------
            text         plain, enriched
            multipart    mixed, alternative, digest, parallel
            message      rfc822, partial, external-body
            application  octet-stream, postscript
            image        jpeg, gif, png
            audio        basic
            video        mpeg

       A legal MIME message must contain a subtype specification.

       To  specify a content, regardless of its subtype, just use
       the name of the content, e.g., "audio".  To specify a spe­
       cific  subtype,  separate  the  two  with  a  slash, e.g.,
       "audio/basic".  Note that regardless of the  values  given
       to the `-type' switch, a multipart content (of any subtype
       listed above) is always acted upon.  Further note that  if
       the  `-type' switch is used, and it is desirable to act on
       a message/external-body content, then the  `-type'  switch
       must  be  used  twice:  once for message/external-body and
       once for the content externally referenced.

   Unseen Sequence
       If the profile  entry  "Unseen-Sequence"  is  present  and
       non-empty,  then  mhshow  will remove each of the messages
       shown from each sequence named by the profile entry.

   Checking the Contents
       The `-check' switch tells mhshow to check each content for
       an  integrity  checksum.  If a content has such a checksum
       (specified as a Content-MD5  header  field),  then  mhshow
       will attempt to verify the integrity of the content.

   Showing the Contents
       The headers of each message are displayed with the mhlproc
       (usually mhl), using the standard format file mhl.headers.
       You  may  specify an alternate format file with the `-form
       formfile' switch.  If the format file mhl.null  is  speci­
       fied,  then  the  display  of  the message headers is sup­
       pressed.

       Next, the contents are extracted from the message and  are
       stored in a temporary file.  Usually, the name of the tem­
       porary file the word "mhshow"  followed  by  a  string  of
       characters.   Occasionally,  the  method used to display a
       content (described next), requires that the file end in  a
       specific  suffix.   For example, the soffice command (part

       MicroSoft  Word  content, but it uses the suffix to deter­
       mine how to display the file.  If no  suffix  is  present,
       the  file is not correctly loaded.  Similarily, older ver­
       sions of the gs command append a ".ps" suffix to the file­
       name  if  one  was  missing.  As a result, these cannot be
       used to read the default temporary file.

       To get around this, your profile can contain lines of  the
       form:

            mhshow-suffix-<type>/<subtype>: <suffix>

       or

            mhshow-suffix-<type>: <suffix>

       to  specify  a  suffix which can be automatically added to
       the temporary file created for a  specific  content  type.
       For example, the following lines might appear in your pro­
       file:

            mhshow-suffix-text: .txt
            mhshow-suffix-application/msword: .doc
            mhshow-suffix-application/PostScript: .ps

       to automatically append a suffix to the temporary files.

       The method used to display the different contents  in  the
       messages  bodies will be determined by a "display string".
       To find the display string, mhshow will first search  your
       profile for an entry of the form:

            mhshow-show-<type>/<subtype>

       to  determine  the  display  string.  If this isn't found,
       mhshow will search for an entry of the form:

            mhshow-show-<type>

       to determine the display string.

       If a display string is found, any  escapes  (given  below)
       will  be  expanded.   The  result  will  be executed under

       display string may contain the following escapes:

            %a  Insert parameters from Content-Type field
            %e  exclusive execution
            %f  Insert filename containing content
            %F  %e, %f, and stdin is terminal not content
            %l  display listing prior to displaying content
            %p  %l, and ask for confirmation
            %s  Insert content subtype
            %d  Insert content description
            %%  Insert the character %

       For  those  display strings containing the e- or F-escape,
       mhshow will execute at most one  of  these  at  any  given
       time.   Although  the  F-escape expands to be the filename
       containing the content, the e-escape has no  expansion  as
       far as the shell is concerned.

       When  the  p-escape  prompts for confirmation, typing INTR
       (usually control-C) will tell mhshow not to  display  that
       content.   The  p-escape can be disabled by specifying the
       switch `-nopause'.  Further, when mhshow is display a con­
       tent,  typing QUIT (usually control-\) will tell mhshow to
       wrap things up immediately.

       Note that if the content being displayed is multipart, but
       not  one  of the subtypes listed above, then the f- and F-
       escapes expand to multiple filenames, one for each  subor­
       dinate content.  Further, stdin is not redirected from the
       terminal to the content.

       If a display string  is  not  found,  mhshow  has  several
       default values:

            mhshow-show-text/plain: %pmoreproc '%F'
            mhshow-show-message/rfc822: %pshow -file '%F'

       If a subtype of type text doesn't have a profile entry, it
       will be treated as text/plain.

       mhshow has default methods for handling multipart messages
       of  subtype mixed, alternative, parallel, and digest.  Any
       unknown subtype  of  type  multipart  (without  a  profile
       entry), will be treated as multipart/mixed.

       If  none  of these apply, then mhshow will check to see if
       the message has an application/octet-stream  content  with
       parameter "type=tar".  If so, mhshow will use an appropri­
       ate command.  If not, mhshow will complain.


            mhshow-show-audio/basic: raw2audio 2>/dev/null | play
            mhshow-show-image: xv '%f'
            mhshow-show-application/PostScript: lpr -Pps

       Note that when using the f- or F-escape, it's a good  idea
       to  use  single-quotes  around  the escape.  This prevents
       misinterpretation by the shell  of  any  funny  characters
       that might be present in the filename.

       Finally,  mhshow  will process each message serially -- it
       won't start showing the next message until  all  the  com­
       mands  executed to display the current message have termi­
       nated.  In the case of a multipart content (of any subtype
       listed  above),  the content contains advice indicating if
       the parts should be displayed  serially  or  in  parallel.
       Because this may cause confusion, particularly on uni-win­
       dow displays, the `-serialonly' switch  can  be  given  to
       tell mhshow to never display parts in parallel.

   Showing Alternate Character Sets
       Because  a  content  of  type text might be in a non-ASCII
       character set, when mhshow encounters a "charset"  parame­
       ter  for this content, it checks if your terminal can dis­
       play this character set  natively.   Mhn  checks  this  by
       examining the the environment variable MM_CHARSET.  If the
       value of this environment variable is equal to  the  value
       of  the charset parameter, then mhshow assumes it can dis­
       play this content without any additional setup.   If  this
       environment  variable  is  not  set,  mhshow will assume a
       value of "US-ASCII".  If the character set cannot be  dis­
       played natively, then mhshow will look for an entry of the
       form:

            mhshow-charset-<charset>

       which should contain a command creating an environment  to
       render the character set.  This command string should con­
       taining a single "%s", which will be  filled-in  with  the
       command to display the content.

       Example entries might be:

            mhshow-charset-iso-8859-1:  xterm -fn '-*-*-medium-r-
            normal-*-*-120-*-*-c-*-iso8859-*' -e %s
       or
            mhshow-charset-iso-8859-1: '%s'

       The first example tells mhshow to start xterm and load the
       appropriate  character  set for that message content.  The
       second example tells mhshow that your pager (or other pro­
       gram handling that content type) can handle that character


       Note that many pagers strip off the high-order bit or have
       problems displaying text  with  the  high-order  bit  set.
       However, the pager less has support for single-octet char­
       acter sets.  The source to less is available on  many  ftp
       sites  carrying  free software.  In order to view messages
       sent in the ISO-8859-1 character set using less, put these
       lines in your .login file:

            setenv LESSCHARSET latin1
            setenv LESS "-f"

       The first line tells less to use the ISO-8859-1 definition
       for determining whether a  character  is  "normal",  "con­
       trol",  or  "binary".   The  second line tells less not to
       warn you if it encounters a file that has non-ASCII  char­
       acters.   Then,  simply  set the moreproc profile entry to
       less, and it will get called  automatically.   (To  handle
       other  single-octet  character  sets, look at the less (1)
       manual entry for information about the  LESSCHARDEF  envi­
       ronment variable.)

   Messages of Type message/partial
       mhshow  cannot  directly display messages of type partial.
       You must reassemble them first into a normal message using
       mhstore.  Check the man page for mhstore for details.

   External Access
       For  contents  of  type message/external-body, mhshow sup­
       ports these access-types:

            afs
            anon-ftp
            ftp
            local-file
            mail-server

       For the "anon-ftp" and "ftp"  access  types,  mhshow  will
       look for the nmh-access-ftp profile entry, e.g.,

            nmh-access-ftp: myftp.sh

       to  determine the pathname of a program to perform the FTP


            domain name of FTP-site
            username
            password
            remote directory
            remote filename
            local filename
            "ascii" or "binary"

       The program should terminate with an exit status  of  zero
       if the retrieval is successful, and a non-zero exit status
       otherwise.

       If this entry is not provided, then mhshow will use a sim­
       ple built-in FTP client to perform the retrieval.

   The Content Cache
       When  mhshow  encounters  an external content containing a
       "Content-ID:" field, and if the  content  allows  caching,
       then depending on the caching behavior of mhshow, the con­
       tent might be read from or written to a cache.

       The caching behavior of  mhshow  is  controlled  with  the
       `-rcache'  and `-wcache' switches, which define the policy
       for reading from, and writing to, the cache, respectively.
       One  of four policies may be specified: "public", indicat­
       ing that mhshow should make use of a publically-accessible
       content  cache;  "private",  indicating that mhshow should
       make use of the user's  private  content  cache;  "never",
       indicating  that  mhshow should never make use of caching;
       and, "ask", indicating that mhshow should ask the user.

       There are two directories where contents  may  be  cached:
       the  profile  entry nmh-cache names a directory containing
       world-readable contents, and, the profile  entry  nmh-pri­
       vate-cache  names a directory containing private contents.
       The former should be an absolute (rooted) directory  name.
       For example,

            nmh-cache: /tmp

       might  be used if you didn't care that the cache got wiped
       after each reboot of the system.   The  latter  is  inter­
       preted  relative  to  the  user's  nmh  directory,  if not
       rooted, e.g.,

            nmh-private-cache: .cache

       (which is the default value).

       Because the display environment in which  mhshow  operates
       may  vary for different machines, mhshow will look for the
       environment variable $MHSHOW.  If present, this  specifies
       the  name  of  an  additional user profile which should be
       read.  Hence, when a user logs in on a particular  display
       device,  this  environment variable should be set to refer
       to a file containing definitions useful for the given dis­
       play  device.   Normally,  only entries that deal with the
       methods to display different content type and subtypes

            mhshow-show-<type>/<subtype>
            mhshow-show-<type>

       need be present  in  this  additional  profile.   Finally,
       mhshow  will  attempt to consult one other additional user
       profile, e.g.,

            /etc/nmh/mhn.defaults

       which is created automatically during nmh installation.


FILES

       $HOME/.mh_profile                    The user profile
       $MHSHOW                              Additional profile entries
       /etc/nmh/mhn.defaults                System default MIME profile entries
       /etc/nmh/mhl.headers                 The headers template


PROFILE COMPONENTS

       Path:                To determine the user's nmh directory
       Current-Folder:      To find the default current folder
       Unseen-Sequence:     To name sequences denoting unseen messages
       mhlproc:             Default program to display message headers
       nmh-access-ftp:      Program to retrieve contents via FTP
       nmh-cache            Public directory to store cached external contents
       nmh-private-cache    Personal directory to store cached external contents
       mhshow-charset-<charsTemplate for environment to render character sets
       mhshow-show-<type>*  Template for displaying contents
       moreproc:            Default program to display text/plain content


SEE ALSO

       mhbuild(1), mhl(1), mhlist(1), mhstore(1), sendfiles(1)
       RFC-934:
          Proposed Standard for Message Encapsulation,
       RFC-2045:
          Multipurpose Internet Mail Extensions (MIME) Part One:
          Format of Internet Message Bodies,
       RFC-2046:
          Multipurpose Internet Mail Extensions (MIME) Part Two:
          Media Types,
       RFC-2047:
          Multipurpose  Internet  Mail  Extensions  (MIME)   Part
       Three:
          Message Header Extensions for Non-ASCII Text,

          Multipurpose Internet Mail Extensions (MIME) Part Four:
          Registration Procedures,
       RFC-2049:
          Multipurpose Internet Mail Extensions (MIME) Part Five:
          Conformance Criteria and Examples.


DEFAULTS

       `+folder' defaults to the current folder
       `msgs' defaults to cur
       `-nocheck'
       `-form mhl.headers'
       `-pause'
       `-rcache ask'
       `-realsize'
       `-noserialonly'
       `-noverbose'
       `-wcache ask'


CONTEXT

       If  a  folder is given, it will become the current folder.
       The last message selected will become the current message.


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