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       mhshow - display MIME messages


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


       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

       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 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
       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 subtypes can be found in

       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
       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

   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

       Next, the contents are extracted from the message and are stored  in  a
       temporary  file.   Usually,  the name of the temporary file is 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
       versions 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>


            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
       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:


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


       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
       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 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

       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

       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
       single-quotes around the escape.  This  prevents  misinterpretation  by
       the  shell  of  any  funny  characters  that  might  be  present in the

       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
       -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”  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:


       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-
            normal-*-*-120-*-*-c-*-iso8859-*’ -e %s


            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

       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
       determining  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(1) for details.

   External Access
       For contents  of  type  message/external-body,  mhshow  supports  these

       ·   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.,


       to determine the pathname of a program to perform the FTP retrieval.

       This program is invoked with these arguments:

            domain name of FTP-site
            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

       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”, 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

       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 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


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


       which is created automatically during nmh installation.


       $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


       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-<charsTe>mplate for environment to render character sets
       mhshow-show-<type>*  Template for displaying contents
       moreproc:            Default program to display text/plain content


       mhbuild(1), mhl(1), mhlist(1), mhstore(1), sendfiles(1)


+folder’ defaults to the current folder
       ‘msgs’ defaults to cur


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