Provided by: nmh_1.7.1-4_amd64 bug


       mhshow - display nmh MIME messages


       mhshow [-help] [-version] [+folder] [msgs] [-file file] [-part number] ...  [-type
            content] ...  [-prefer content] ...  [-noprefer] [-concat | -noconcat] [-textonly |
            -notextonly] [-inlineonly | -noinlineonly] [-header | -noheader] [-form formfile]
            [-markform formfile] [-rcache policy] [-wcache policy] [-check | -nocheck]


       The mhshow command displays contents of a MIME (multi-media)  message,  or  collection  of

       mhshow  manipulates  multi-media messages as specified in RFC 2045 to 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 only the text parts of a message that are not marked as
       attachments.  This behavior can be changed by the -notextonly and -noinlineonly  switches.
       In  addition,  by  using the -part, -type, and -prefer switches, you may limit and reorder
       the set of parts to be displayed, based on part number and/or content type.  The inclusion
       of  any  -part  or  -type  switches  will  override  the default settings of -textonly and

       The -header switch controls whether mhshow will print a message  separator  header  before
       each  message that it displays.  The header format can be controlled using -headerform, to
       specify a file containing mh-format(5) instructions.   A  copy  of  the  built-in  default
       headerform  can  be  found  in  /etc/nmh/mhshow.header, for reference.  In addition to the
       normal  set  of  mh-format(5)  instructions,  a  "%{folder}"  escape  provides  a   string
       representing the current folder.

       By default, mhshow will concatenate all content under one pager.  If you want each part to
       be displayed separately, you can override the default behavior with -noconcat.

       The -file file switch 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)).

       The  -part  switch  can  be given (one or more times) to restrict the set of subparts that
       will be displayed.  (Obviously with no -part switches, all parts will be considered.)   If
       a  -part  switch  specifies a specific subpart (i.e., a "leaf" in the tree of MIME parts),
       then  that  part  will  always  be  displayed.    If   a   -part   switch   references   a
       multipart/alternative  part,  then  (in  the  absence  of a -type switch) only the default
       subpart of that multipart will be displayed.

       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 only for
       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.

       The -type switch can also be used to restrict (or, when used in conjunction with -part, to
       further  restrict)  the  display  of  parts  according to content type.  One or more -type
       switches part will only select the first match from a multipart/alternative, even if there
       is more than one subpart that matches (one of) the given content type(s).

       Using  either -part or -type switches alone will cause either switch to select the part(s)
       they match.  Using them together will select only the part(s) matched by  both  (sets  of)
       switches.   In  other  words,  the result is the intersection, and not the union, of their
       separate match results.

       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  message/external-body  and  once  for  the
       content externally referenced.

       In  the  absence  of  -prefer,  mhshow  will  select  the  "best" displayable subpart from
       multipart/alternative content.  The -prefer switch can be used  (one  or  more  times,  in
       order   of   ascending   preference)   to   let   MH  know  which  content  types  from  a
       multipart/alternative MIME part are preferred by  the  user,  in  order  to  override  the
       default  selection for display.  For example, mail is often sent containing both plaintext
       and HTML-formatted versions of the same content, and the HTML version is usually indicated
       to  be the "best" format for viewing.  Using “-prefer text/plain” will cause the plaintext
       version to be displayed if possible, but still allow display of the HTML part if there  is
       no  plaintext subpart available.  Using “-prefer text/plain -prefer image/png” would add a
       preference  for  PNG  images,  which  might  or  might  not  ever  appear  in   the   same
       multipart/alternative  section  with  text/plain.  Implementation note:  RFC 2046 requires
       that the subparts of a multipart/alternative be ordered according to "faithfulness to  the
       original  content",  and  MH by default selects the subpart ranked most "faithful" by that
       ordering.  The -prefer switch reorders  the  alternative  parts  (only  internally,  never
       changing  the  message  file)  to move the user's preferred part(s) to the "most faithful"
       position.  Thus, when viewed by mhlist, the ordering of multipart/alternative  parts  will
       appear to change when invoked with or without various -prefer switches.  Since the last of
       multiple -prefer options "wins", a -prefer on the command line  will  override  any  in  a
       profile entry.

       The -noprefer switch will cancel any previous -prefer switches.

   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 alternative 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 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.  Similarly, 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:


       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
            %{parameter} Insert the parameter value from the Content-Type field
            %f           Insert filename containing content
            %F           %f, and stdin is terminal not content
            %l           display listing prior to displaying content
            %s           Insert content subtype
            %d           Insert content description
            %%           Insert the character %

       mhshow will execute at most one display string at any given time, and wait for the current
       display string to finish execution before executing the next display string.

       The  {parameter}  escape  is typically used in a command line argument that should only be
       present if it has a non-null value.  It is highly recommended that the  entire  escape  be
       wrapped  in double quotes.  Shell parameter expansion can construct the argument only when
       it is non-null, e.g.,

            mhshow-show-text/html: charset="%{charset}";
              w3m ${charset:+-I $charset} -T text/html %F

       That example also shows the use of indentation to signify continuation: the two text lines
       combine  to form a single entry.  Note that when dealing with text that has been converted
       internally by iconv(3), the “charset” parameter will reflect the target character  set  of
       the text, rather than the original character set in the message.

       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.  Furthermore, stdin is not redirected from the terminal to the content.

       If a display string is not found, mhshow behaves as if these profile entries were supplied
       and supported:

            mhshow-show-text/plain: %lmoreproc %F
            mhshow-show-message/rfc822: %lshow -file %F

       Note that “moreproc” is not supported in user profile display strings.

       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
       appropriate command.  If not, mhshow will complain.

       Example entries might be:

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

       If an f- or F-escape is not quoted with single quotes, its expansion will be wrapped  with
       single quotes.

       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.

   Showing Alternate Character Sets
       If mhshow was built with iconv(3), then all text/plain parts of  the  message(s)  will  be
       displayed  using the character set of the current locale.  See the mhparam(1) man page for
       how to determine whether your nmh installation includes iconv(3) support.  To convert text
       parts  other  than  text/plain, or if mhshow was not built with iconv, an external program
       can be used, as described next.

       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.  mhshow checks this by examining the  current  character  set
       defined  by the locale(1) environment variables.  If the value of the locale character set
       is equal to the value of the charset parameter, then mhshow assumes it  can  display  this
       content  without  any  additional  setup.   If the locale is not set properly, 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 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.   For  example, messages encoded in the ISO-8859-1 character set can be viewed using
       less, with these environment variable settings:

            LESSCHARSET latin1
            LESS        -f

       The first setting tells less to use the  ISO-8859-1  definition  to  determine  whether  a
       character  is “normal”, “control“, or “binary”.  The second setting 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 first reassemble them
       into a normal message using mhstore.  Check mhstore(1) for details.

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

       ·   afs

       ·   anon-ftp

       ·   ftp

       ·   local-file

       ·   mail-server

       ·   url

       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.

       For the “url” access-type, mhshow will look for the “nmh-access-url” profile  entry.   See
       mhstore(1) for more details.

   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 writing to, the cache, respectively.  One of  four
       policies may be specified: “public”, indicating that mhshow should make use of a publicly-
       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


       need be present in this additional profile.  Finally, mhshow will attempt to consult


       which is created automatically during nmh installation.

       See  "Profile Lookup" in mh-profile(5) for the profile search order, and for how duplicate
       entries are treated.

   Content-Type Marker
       mhshow will display a marker containing information about the part being  displayed  next.
       The  default marker can be changed using the -markform switch to specify a file containing
       mh-format(5) instructions to use when displaying  the  content  marker.   A  copy  of  the
       default  markform  can  be found in /etc/nmh/mhshow.marker, for reference.  In addition to
       the  normal  set  of  mh-format(5)  instructions,  the  following  component  escapes  are

            Escape          Returns   Description
            part            string    MIME part number
            content-type    string    MIME Content-Type of part
            description     string    Content-Description header
            disposition     string    Content disposition (attachment or inline)
            ctype-<PARAM>   string    Value of <PARAM> from Content-Type header
            cdispo-<PARAM>  string    Value of <PARAM> from
                                      Content-Disposition header
            %(size)         integer   The size of the decoded part, in bytes
            %(unseen)       boolean   Returns true for suppressed parts
            In  this  context, the %(unseen) function indicates whether mhshow has decided to not
            display a particular part due to the -textonly or -inlineonly switches.
       All MIME parameters and the “Content-Description”  header  will  have  RFC  2231  decoding
       applied and be converted to the local character set.


       mhshow  looks  for  all  format  files  and  mhn.defaults  in multiple locations: absolute
       pathnames are accessed directly, tilde expansion is  done  on  usernames,  and  files  are
       searched  for  in  the user's Mail directory, as specified in their profile.  If not found
       there, the directory “/etc/nmh” is checked.

       $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
       /etc/nmh/mhshow.marker     Example content marker
       /etc/nmh/mhshow.header     Example message separator header


       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-access-url:      Program to retrieve contents via HTTP
       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


       iconv(3), mhbuild(1), mhl(1), mhlist(1), mhparam(1), mhstore(1), sendfiles(1)


       `+folder' defaults to the current folder
       `msgs' defaults to cur
       `-form mhl.headers'
       `-rcache ask'
       `-wcache ask'


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