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MHSHOW(1mh)                                                                           MHSHOW(1mh)

NAME
       mhshow - display nmh MIME messages

SYNOPSIS
       mhshow [-help] [-version] [+folder] [msgs] [-file file] [-part number] ...  [-type con-
            tent] ...  [-prefer content] ...  [-noprefer] [-concat | -noconcat] [-textonly | -no-
            textonly] [-inlineonly | -noinlineonly] [-header | -noheader] [-form formfile]
            [-markform formfile] [-rcache policy] [-wcache policy] [-check | -nocheck]

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

       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 -inli-
       neonly.

       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 head-
       erform  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  stan-
       dard  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/alter-
       native part, then (in the absence of a -type switch) only the default subpart of that mul-
       tipart 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, respec-
       tively.  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/ba-
       sic".   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  exter-
       nally referenced.

       In  the  absence of -prefer, mhshow will select the "best" displayable subpart from multi-
       part/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 avail-
       able.  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/al-
       ternative be ordered according to "faithfulness to the original content", and  MH  by  de-
       fault selects the subpart ranked most "faithful" by that ordering.  The -prefer switch re-
       orders 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 mh-
       list, 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 con-
       tent has such a checksum (specified as a Content-MD5 header field), then mhshow  will  at-
       tempt to verify the integrity of the content.

   Showing the Contents
       The  headers of each message are displayed with the mhlproc (usually mhl), using the stan-
       dard 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 mes-
       sage 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 char-
       acters.  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>

       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 bodies  will  be  deter-
       mined  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>

       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
            %{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 applica-
       tion/octet-stream content with parameter "type=tar".  If so, mhshow will use an  appropri-
       ate 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 mes-
       sage 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 encoun-
       ters 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:

            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-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  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 char-
       acter 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 pro-
       file 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 en-
       vironment 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:

       o   afs

       o   anon-ftp

       o   ftp

       o   local-file

       o   mail-server

       o   url

       For  the "anon-ftp" and "ftp" access types, mhshow will look for the "nmh-access-ftp" pro-
       file 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.

       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 par-
       ticular display device, this environment variable should be set to refer to  a  file  con-
       taining 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

            /etc/nmh/mhn.defaults

       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 de-
       fault 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 supported:

            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  ap-
       plied and be converted to the local character set.

FILES
       mhshow  looks  for all format files and mhn.defaults in multiple locations: absolute path-
       names 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

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

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

DEFAULTS
       `+folder' defaults to the current folder
       `msgs' defaults to cur
       `-nocheck'
       `-concat'
       `-textonly'
       `-inlineonly'
       `-form mhl.headers'
       `-rcache ask'
       `-wcache ask'

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

nmh-1.7.1                                   2015-02-08                                MHSHOW(1mh)

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