Computer Science
MHN(1) MHN(1)
NAME
mhn - display/list/store/cache MIME messages
SYNOPSIS
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]
DESCRIPTION
The mhn command allows you to display, list, store, or
cache the contents 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 RFC-2047.
The switches `-list', `-show', `-store', and `-cache'
direct the operation 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 messages. By using
the `-part' and `-type' switches, you may limit the scope
of the given operation to particular subparts (of a multi-
part 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 exe-
cute the mhbuild command. 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 standard input. Note
that the file, or input from standard input should be a
validly formatted message, just like any other nmh mes-
sage. 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 sepa-
rated by dots. For example, in a multipart content con-
taining three parts, these would be named as 1, 2, and 3,
respectively. If part 2 was also a multipart content con-
taining 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 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 spe-
cific 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.
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 content.
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 displayed above the listing. The `-realsize'
switch tells mhn to evaluate the "native" (decoded) format
of each content prior to listing. This provides an accu-
rate count at the expense of a small delay. If the `-ver-
bose' 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.
The `-show' switch tells mhn to display the contents of
the named messages.
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 speci-
fied, then the display of the message headers is sup-
pressed.
The method used to display the different contents in the
messages bodies will be determined by a "display string".
To find the display string, mhn will first search your
profile for an entry of the form:
mhn-show-<type>/<subtype>
to determine the display string. If this isn't found, mhn
will search for an entry of the form:
mhn-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,
mhn will execute at most one of these at any given time.
Although the F-escape expands to be the filename contain-
ing 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 mhn not to display that con-
tent. The p-escape can be disabled by specifying the
switch `-nopause'. Further, when mhn is display a con-
tent, 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 subor-
dinate 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 multipart/mixed.
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 single-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 showing the next message until all the com-
mands executed to display the current message have termi-
nated. 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-win-
dow displays, the `-serialonly' switch can be given to
tell mhn to never display parts in parallel.
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:
mhn-charset-<charset>
which should contain a command creating an environment to
render the character set. This command string should con-
taining 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
or
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 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 char-
acter 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 determing 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 sin-
gle-octet character sets, look at the less (1) manual
entry for information about the LESSCHARDEF environment
variable.)
The `-store' switch tells mhn to store the contents of the
named messages 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 mhn-storage profile entry, e.g.,
mhn-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 contains 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:
mhn-store-<type>/<subtype>
to determine the formatting string. If this isn't found,
mhn will look for an entry of the form:
mhn-store-<type>
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 "-" charac-
ter, then the content is sent to the standard output.
If the formatting string starts with a '|', then the dis-
play 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 mhn-storage or the current working directory.
Any escapes (given below) will be expanded, except for the
a-escape.
A command or pathname formatting string may contain the
following escapes. If the content isn't part of a multi-
part (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 file-
name. If the content is not application/octet-stream,
then mhn will check to see if the content is a message.
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 > %m%P.au
mhn-store-image/jpeg: %m%P.jpg
mhn-store-application/PostScript: %m%P.ps
When asked to store a content containing a partial mes-
sage, mhn will try to locate all of the portions and com-
bine them accordingly. The default is to store the com-
bined parts as a new message in the current folder,
although this can be changed using formatting strings as
discussed 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 -)
type=tar
conversions=compress
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.
For contents of type message/external-body, mhn supports
these access-types:
afs
anon-ftp
ftp
local-file
mail-server
For the "anon-ftp" and "ftp" access types, mhn will look
for the mhn-access-ftp profile entry, e.g.,
mhn-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 mhn will use a simple
built-in FTP client to perform the retrieval.
When mhn encounters an external content containing a "Con-
tent-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 writing to, the cache, respectively.
One of four policies may be specified: "public", indicat-
ing 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", indicat-
ing 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 mhn-cache names a directory containing
world-readable contents, and, the profile entry mhn-pri-
vate-cache names a directory containing private contents.
The former should be an absolute (rooted) directory name.
For example,
mhn-cache: /tmp
might be used if you didn't care that the cache got wiped
after each reboot of the system. The latter is inter-
preted relative to the user's nmh directory, if not
rooted, e.g.,
mhn-private-cache: .cache
(which is the default value).
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 corresponds to the value in the original mes-
sage/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
...
Because the display environment in which mhn operates may
vary for different machines, mhn will look for the envi-
ronment variable $MHN. If present, this specifies the
name of an additional user profile which should be read.
Hence, when a user logs in on a particular display device,
this environment variable should be set to refer to a file
containing definitions useful for the given display
device. Normally, only entries that deal with the methods
to display different content type and subtypes
mhn-show-<type>/<subtype>
mhn-show-<type>
need be present in this additional profile. Finally, mhn
will attempt to consult one other additional user profile,
e.g.,
/etc/nmh/mhn.defaults
which is created automatically during nmh installation.
^$HOME/.mh_profile~^The user profile ^$MHN~^Additional
profile entries ^/etc/nmh/mhn.defaults~^System-default
profile entries ^/etc/nmh/mhl.headers~^The headers tem-
plate ^Path:~^To determine the user's nmh directory ^Cur-
rent-Folder:~^To find the default current folder ^mhl-
proc:~^Default program to display message headers ^mhn-
access-ftp:~^Program to retrieve contents via FTP ^mhn-
cache~^Public directory to store cached external contents
^mhn-charset-<charset>~^Template for environment to render
character sets ^mhn-private-cache~^Personal directory to
store cached external contents ^mhn-show-<type>*~^Template
for displaying contents ^mhn-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)
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. `+folder' defaults
to the current folder `msgs' defaults to cur `-noauto'
`-nocache' `-nocheck' `-form mhl.headers' `-headers'
`-pause' `-rcache ask' `-realsize' `-noserialonly' `-show'
`-noverbose' `-wcache ask' If a folder is given, it will
become the current folder. The last message selected will
become the current message. Partial messages contained
within a multipart content are not reassembled with the
`-store' switch.
[nmh-0.27] MH.6.8 1
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