MHN(1)                                                                  MHN(1)


       mhn - display/list/store/cache MIME messages


       mhn [+folder] [msgs] [-file file]
            [-part number]... [-type content]...
            [-show] [-noshow] [-list] [-nolist]
            [-store] [-nostore] [-cache] [-nocache]
            [-headers] [-noheaders] [-realsize] [-norealsize]
            [-serialonly] [-noserialonly] [-form formfile]
            [-pause] [-nopause] [-auto] [-noauto]
            [-rcache policy] [-wcache policy] [-check] [-nocheck]
            [-verbose] [-noverbose] [-version] [-help]

     mhn -build file
            [-ebcdicsafe] [-noebcdicsafe]
            [-rfc934mode] [-norfc934mode]



       The mhn command allows you to display, list, store, or cache  the  con-
       tents of a MIME (multi-media) messages.

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

       The switches `-list', `-show', `-store', and `-cache' direct the opera-
       tion  of mhn.  Only one of these switches may be used at a time.  These
       switches are used to operate on the content of each of the  named  mes-
       sages.   By  using  the `-part' and `-type' switches, you may limit the
       scope of the given operation to particular  subparts  (of  a  multipart
       content) and/or particular content types.

       The  switch  `-build'  is  used to construct a MIME message.  It is for
       backward compatibility and instructs mhn to execute  the  mhbuild  com-
       mand.   It is preferred that you use the mhbuild command directly.  See
       the mhbuild(1) man page for details.

       The option `-file file' directs mhn to use the specified  file  as  the
       source  message,  rather  than a message from a folder.  If you specify
       this file as "-", then mhn will accept the source message on the  stan-
       dard 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 for-
       mat 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.

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

   Listing the Contents
       The `-list' switch tells mhn to list the table of  contents  associated
       with the named messages.

       The  `-headers'  switch indicates that a one-line banner should be dis-
       played above the listing.  The `-realsize' switch tells mhn to evaluate
       the  "native"  (decoded) format of each content prior to listing.  This
       provides an accurate count at the expense of a  small  delay.   If  the
       `-verbose'  switch  is  present, then the listing will show any "extra"
       information that is present in the message, such  as  comments  in  the
       Content-Type header.

   Showing the Contents
       The  `-show' switch tells mhn to display the contents of the named mes-

       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 the word "mhn"
       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 StarOf-
       fice  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:

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


            mhn-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:

            mhn-suffix-text: .txt
            mhn-suffix-application/msword: .doc
            mhn-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, mhn will first search your profile for an entry of the form:


       to determine the display string.  If this isn't found, mhn 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

            %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, mhn will  exe-
       cute  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 mhn not to display that content.  The p-escape can be
       disabled  by  specifying  the  switch `-nopause'.  Further, when mhn is
       display a content, typing QUIT (usually control-\)  will  tell  mhn  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, mhn has several default values:

            mhn-show-text/plain: %pmoreproc '%F'
            mhn-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.

       mhn  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-

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

       Example entries might be:

            mhn-show-audio/basic: raw2audio 2>/dev/null | play
            mhn-show-image: xv '%f'
            mhn-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, mhn will process each message serially -- it won't start show-
       ing  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 mhn to never display parts in  par-

   Showing Alternate Character Sets
       Because  a  content of type text might be in a non-ASCII character set,
       when mhn 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 mhn assumes it can display  this  content  without  any
       additional  setup.   If  this environment variable is not set, mhn will
       assume a value of "US-ASCII".  If the character set cannot be displayed
       natively, then mhn 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:

            mhn-charset-iso-8859-1:      xterm     -fn     '-*-*-medium-r-nor-
            mal-*-*-120-*-*-c-*-iso8859-*' -e %s
            mhn-charset-iso-8859-1: '%s'

       The first example tells mhn to start xterm  and  load  the  appropriate
       character  set  for that message content.  The second example tells mhn
       that your pager (or other program handling that content type) can  han-
       dle  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 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.)

   Storing the Contents
       The  `-store'  switch tells mhn to store the contents of the named mes-
       sages in "native" (decoded) format.  Two things must be determined: the
       directory  to  store the content, and the filenames.  Files are written
       in the directory given by the nmh-storage profile entry, e.g.,

            nmh-storage: /tmp

       If this entry isn't present, the current working directory is used.

       If the `-auto' switch is given, then mhn will check if the message con-
       tains  information indicating the filename that should be used to store
       the content.  This information should be  specified  as  the  attribute
       "name=filename"  in  the  Content-Type  header  for the content you are
       storing.  For security reasons, this filename will  be  ignored  if  it
       begins  with the character '/', '.', '|', or '!', or if it contains the
       character '%'.  For the sake  of  security,  this  switch  is  not  the
       default,  and  it is recommended that you do NOT put the `-auto' switch
       in your .mh_profile file.

       If the `-auto' switch is not given (or is being  ignored  for  security
       reasons)  then  mhn  will  look in the user's profile for a "formatting
       string" to determine how  the  different  contents  should  be  stored.
       First, mhn will look for an entry of the form:


       to determine the formatting string.  If this isn't found, mhn will look
       for an entry of the form:


       to determine the formatting string.

       If the formatting string starts with a "+" character, then  content  is
       stored in the named folder.  A formatting string consisting solely of a
       "+" character is interpreted to be the current folder.

       If the formatting string consists solely of a "-" character,  then  the
       content is sent to the standard output.

       If  the  formatting  string  starts with a '|', then the display string
       will represent a command for mhn to  execute  which  should  ultimately
       store the content.  The content will be passed to the standard input of
       the command.  Before the command is executed, mhn will  change  to  the
       appropriate  directory,  and  any  escapes (given below) in the display
       string will be expanded.

       Otherwise the formatting string will represent a pathname in  which  to
       store  the  content.   If the formatting string starts with a '/', then
       the content will be stored in the full path given, else the  file  name
       will  be  relative  to  the value of nmh-storage or the current working
       directory.  Any escapes (given below) will be expanded, except for  the

       A  command  or  pathname  formatting  string  may contain the following
       escapes.  If the content isn't part of  a  multipart  (of  any  subtype
       listed above) content, the p-escapes are ignored.

            %a  Parameters from Content-type  (only valid with command)
            %m  Insert message number
            %P  Insert part number with leading dot
            %p  Insert part number without leading dot
            %t  Insert content type
            %s  Insert content subtype
            %%  Insert character %

       If  no formatting string is found, mhn will check to see if the content
       is application/octet-stream with parameter "type=tar".  If so, mhn will
       choose  an  appropriate  filename.   If  the  content  is  not applica-
       tion/octet-stream, then mhn will check to see if the content is a  mes-
       sage.   If  so, mhn will use the value "+".  As a last resort, mhn will
       use the value "%m%P.%s".

       Example profile entries might be:

            mhn-store-text: %m%P.txt
            mhn-store-text: +inbox
            mhn-store-message/partial: +
            mhn-store-audio/basic: | raw2audio -e ulaw -s 8000 -c 1 >
            mhn-store-image/jpeg: %m%P.jpg

   Reassembling Messages of Type message/partial
       When asked to store a content containing a partial  message,  mhn  will
       try  to  locate  all of the portions and combine them accordingly.  The
       default is to store the combined parts as a new message in the  current
       folder,  although  this can be changed using formatting strings as dis-
       cussed above.  Thus, if someone has sent you a message in several parts
       (such as the output from sendfiles), you can easily reassemble them all
       into a single message in the following fashion:

            % mhn -list 5-8
             msg part  type/subtype             size description
               5       message/partial           47K part 1 of 4
               6       message/partial           47K part 2 of 4
               7       message/partial           47K part 3 of 4
               8       message/partial           18K part 4 of 4
            % mhn -store 5-8
            reassembling partials 5,6,7,8 to folder inbox as message 9
            % mhn -list -verbose 9
             msg part  type/subtype             size description
               9       application/octet-stream 118K
                         (extract with uncompress | tar xvpf -)

       This will store exactly one message, containing the sum of  the  parts.
       It  doesn't  matter  whether the partials are specified in order, since
       mhn will sort the partials, so that they are combined  in  the  correct
       order.  But if mhn can not locate every partial necessary to reassemble
       the message, it will not store anything.

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


       For  the  "anon-ftp" and "ftp" access types, mhn 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 mhn will use a simple built-in  FTP
       client to perform the retrieval.

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

       The caching behavior of  mhn  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 mhn should make use of a publically-
       accessible content cache; "private", indicating that  mhn  should  make
       use  of  the user's private content cache; "never", indicating that mhn
       should never make use of  caching;  and,  "ask",  indicating  that  mhn
       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).

   Caching the Contents
       When  you encounter a content of type message/external-body with access
       type "mail-server", mhn will ask you if may send a message to  a  mail-
       server requesting the content, e.g.,

            % show 1
            Retrieve content by asking mail-server@...

            SEND file

            ? yes
            mhn: request sent

       Regardless  of your decision, mhn can't perform any other processing on
       the content.

       However, if mhn is  allowed  to  request  the  content,  then  when  it
       arrives,  there  should be a top-level "Content-ID:" field which corre-
       sponds to the value in the original message/external-body content.  You
       should  now  use  the `-cache' switch to tell mhn to enter the arriving
       content into the content cache, e.g.,

            % mhn -cache 2
            caching message 2 as file ...

       You can then re-process the original message/external-body content, and
       "the right thing should happen", e.g.,

            % show 1

   User Environment
       Because the display environment in which mhn operates may vary for dif-
       ferent machines, mhn will look for the environment variable  $MHN.   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 con-
       taining 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, mhn will  attempt
       to consult one other additional user profile, e.g.,


       which is created automatically during nmh installation.


       $HOME/.mh_profile                    The user profile
       $MHN                                 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
       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
       mhn-charset-<charset>Template for environment to render character sets
       mhn-show-<type>*     Template for displaying contents
       nmh-storage          Directory to store contents
       mhn-store-<type>*    Template for storing contents
       moreproc:            Default program to display text/plain content


       mhbuild(1), mhl(1), sendfiles(1)
          Proposed Standard for Message Encapsulation,
          Multipurpose Internet Mail Extensions (MIME) Part One:
          Format of Internet Message Bodies,
          Multipurpose Internet Mail Extensions (MIME) Part Two:
          Media Types,
          Multipurpose Internet Mail Extensions (MIME) Part Three:
          Message Header Extensions for Non-ASCII Text,
          Multipurpose Internet Mail Extensions (MIME) Part Four:
          Registration Procedures,
          Multipurpose Internet Mail Extensions (MIME) Part Five:
          Conformance Criteria and Examples.


       `+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 mes-
       sage selected will become the current message.


       Partial messages contained within a multipart content are not  reassem-
       bled with the `-store' switch.

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

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