MHSHOW(1)MHSHOW(1)NAMEmhshow - display MIME messages
SYNOPSISmhshow [+folder] [msgs] [-file file]
[-part number]... [-type content]...
[-serialonly] [-noserialonly] [-pause] [-nopause]
[-check] [-nocheck] [-form formfile]
[-rcache policy] [-wcache policy]
[-verbose] [-noverbose] [-version] [-help]
DESCRIPTION
The mhshow command display contents of a MIME (multi-
media) message or collection of messages.
mhshow manipulates multi-media messages as specified in
RFC-2045 thru RFC-2049. Currently mhshow only supports
encodings in message bodies, and does not support the
encoding of message headers as specified in RFC-2047.
By default mhshow will display all parts of a multipart
message. By using the `-part' and `-type' switches, you
may limit the scope of mhshow to particular subparts (of a
multipart content) and/or particular content types.
The option `-file file' directs mhshow to use the speci-
fied 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 mes-
sages, 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
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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.
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 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.
Next, the contents are extracted from the message and are
stored in a temporary file. Usually, the name of the tem-
porary file 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
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of the StarOffice package) can be used to display
MicroSoft Word content, but it uses the suffix to deter-
mine how to display the file. If no suffix is present,
the file is not correctly loaded. Similarily, older ver-
sions of the gs command append a ".ps" suffix to the file-
name 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 pro-
file:
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:
mhshow-show-<type>/<subtype>
to determine the display string. 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
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/bin/sh, with the standard input set to the content. The
display string may contain the following escapes:
%a Insert parameters from Content-Type field
%e exclusive execution
%f Insert filename containing content
%F %e, %f, and stdin is terminal not content
%l display listing prior to displaying content
%p %l, and ask for confirmation
%s Insert content subtype
%d Insert content description
%% Insert the character %
For those display strings containing the e- or F-escape,
mhshow will execute at most one of these at any given
time. Although the F-escape expands to be the filename
containing the content, the e-escape has no expansion as
far as the shell is concerned.
When the p-escape prompts for confirmation, typing INTR
(usually control-C) will tell mhshow not to display that
content. The p-escape can be disabled by specifying the
switch `-nopause'. Further, when mhshow is display a con-
tent, typing QUIT (usually control-\) will tell mhshow to
wrap things up immediately.
Note that if the content being displayed is multipart, but
not one of the subtypes listed above, then the f- and F-
escapes expand to multiple filenames, one for each subor-
dinate content. Further, stdin is not redirected from the
terminal to the content.
If a display string is not found, mhshow has several
default values:
mhshow-show-text/plain: %pmoreproc '%F'
mhshow-show-message/rfc822: %pshow -file '%F'
If a subtype of type text doesn't have a profile entry, it
will be treated as text/plain.
mhshow has default methods for handling multipart messages
of subtype mixed, alternative, parallel, and digest. Any
unknown subtype of type multipart (without a profile
entry), will be treated as 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 appropri-
ate command. If not, mhshow will complain.
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Example entries might be:
mhshow-show-audio/basic: raw2audio 2>/dev/null | play
mhshow-show-image: xv '%f'
mhshow-show-application/PostScript: lpr -Pps
Note that when using the f- or F-escape, it's a good idea
to use single-quotes around the escape. This prevents
misinterpretation by the shell of any funny characters
that might be present in the filename.
Finally, mhshow 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 mhshow to never display parts in parallel.
Showing Alternate Character Sets
Because a content of type text might be in a non-ASCII
character set, when mhshow encounters a "charset" parame-
ter for this content, it checks if your terminal can dis-
play this character set natively. Mhn checks this by
examining the the environment variable MM_CHARSET. If the
value of this environment variable is equal to the value
of the charset parameter, then mhshow assumes it can dis-
play this content without any additional setup. If this
environment variable is not set, mhshow will assume a
value of "US-ASCII". If the character set cannot be dis-
played 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 con-
taining 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 pro-
gram handling that content type) can handle that character
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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 determining whether a character is "normal", "con-
trol", or "binary". The second line tells less not to
warn you if it encounters a file that has non-ASCII char-
acters. 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 envi-
ronment variable.)
Messages of Type message/partial
mhshow cannot directly display messages of type partial.
You must reassemble them first into a normal message using
mhstore. Check the man page for mhstore for details.
External Access
For contents of type message/external-body, mhshow sup-
ports these access-types:
afs
anon-ftp
ftp
local-file
mail-server
For the "anon-ftp" and "ftp" access types, mhshow will
look for the nmh-access-ftp profile entry, e.g.,
nmh-access-ftp: myftp.sh
to determine the pathname of a program to perform the FTP
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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 mhshow will use a sim-
ple built-in FTP client to perform the retrieval.
The Content Cache
When mhshow encounters an external content containing a
"Content-ID:" field, and if the content allows caching,
then depending on the caching behavior of mhshow, the con-
tent 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", indicat-
ing that mhshow should make use of a publically-accessible
content cache; "private", indicating that mhshow should
make use of the user's private content cache; "never",
indicating that mhshow should never make use of caching;
and, "ask", indicating that mhshow should ask the user.
There are two directories where contents may be cached:
the profile entry nmh-cache names a directory containing
world-readable contents, and, the profile entry nmh-pri-
vate-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 inter-
preted relative to the user's nmh directory, if not
rooted, e.g.,
nmh-private-cache: .cache
(which is the default value).
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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 dis-
play 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 one other additional user
profile, e.g.,
/usr/contrib/mh/etc/mhn.defaults
which is created automatically during nmh installation.
FILES
$HOME/.mh_profile The user profile
$MHSHOW Additional profile entries
/usr/contrib/mh/etc/mhn.defaults System default MIME profile entries
/usr/contrib/mh/etc/mhl.headers The headers template
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-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 ALSOmhbuild(1), mhl(1), mhlist(1), mhstore(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,
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RFC-2048:
Multipurpose Internet Mail Extensions (MIME) Part Four:
Registration Procedures,
RFC-2049:
Multipurpose Internet Mail Extensions (MIME) Part Five:
Conformance Criteria and Examples.
DEFAULTS
`+folder' defaults to the current folder
`msgs' defaults to cur
`-nocheck'
`-form mhl.headers'
`-pause'
`-rcache ask'
`-realsize'
`-noserialonly'
`-noverbose'
`-wcache ask'
CONTEXT
If a folder is given, it will become the current folder.
The last message selected will become the current message.
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