mhshow



MHSHOW(1)                                                            MHSHOW(1)




NAME

       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 particu-
       lar content types.

       The option `-file file' directs mhshow to use the specified 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 messages, see inc (1)).

       A part specification consists of a series of numbers separated by dots.
       For example, in a multipart content containing three parts, these would
       be named as 1, 2, and 3, respectively.  If part 2 was also a  multipart
       content  containing  two  parts,  these  would be named as 2.1 and 2.2,
       respectively.  Note that the `-part' switch is effective for only  mes-
       sages 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 subtypes can be  found  in
       RFC-2046.  A list of commonly 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 specific 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  mes-
       sage/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 specified, then the display of the message headers is
       suppressed.

       Next, the contents are extracted from the message and are stored  in  a
       temporary  file.   Usually,  the  name  of  the temporary 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  of  the
       StarOffice  package) can be used to display MicroSoft Word content, but
       it uses the suffix to determine 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  filename  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 profile:

            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  bod-
       ies  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 /bin/sh, with the standard
       input set to the content.  The 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  con-
       trol-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 content, 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 subordinate 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  multi-
       part/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 appropriate command.  If not, mhshow will com-
       plain.

       Example entries might be:

            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  sin-
       gle-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 commands executed to display the
       current message have terminated.  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-window displays, the `-seri-
       alonly' 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"  parameter  for  this  content,  it
       checks  if  your terminal can display 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  display  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 displayed 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 containing  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-nor-
            mal-*-*-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 program handling  that  content  type)
       can handle that character set, and that no special processing is needed
       beforehand.

       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 character 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 deter-
       mining whether a character is "normal", "control",  or  "binary".   The
       second line tells less not to warn you if it encounters a file that has
       non-ASCII characters.  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 environment 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  supports 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 retrieval.
       This program is invoked with these arguments:

            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 simple 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 content 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 writ-
       ing  to,  the  cache, respectively.  One of four policies may be speci-
       fied: "public", indicating 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-private-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 interpreted relative to the user's
       nmh directory, if not rooted, e.g.,

            nmh-private-cache: .cache

       (which is the default value).


   User Environment
       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 display
       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,
       RFC-2048:
          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 mes-
       sage selected will become the current message.



[nmh-1.0.4]                         MH.6.8                           MHSHOW(1)

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