mhshow - display MIME messages
mhshow [+folder] [msgs] [-file file]
[-part number]... [-type content]...
[-serialonly] [-noserialonly] [-pause] [-nopause]
[-check] [-nocheck] [-form formfile]
[-rcache policy] [-wcache policy]
[-verbose] [-noverbose] [-version] [-help]
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
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 particu-
lar content types.
The option `-file file' 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)).
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:
text plain, enriched
multipart mixed, alternative, digest, parallel
message rfc822, partial, external-body
application octet-stream, postscript
image jpeg, gif, png
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.
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
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 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
"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. Similarily, older ver-
sions 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
To get around this, your profile can contain lines of the form:
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:
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, mhshow will first search your profile for an entry of the form:
to determine the display string. 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
%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 con-
trol-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 content, 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 subordinate 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 multi-
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 com-
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 sin-
gle-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 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 mhshow to never display parts in
Showing Alternate Character Sets
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. 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 display 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 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-nor-
mal-*-*-120-*-*-c-*-iso8859-*' -e %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
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.)
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.
For contents of type message/external-body, mhshow supports these
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
"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 simple 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 content might be read from or written to a
The caching behavior of mhshow 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 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-private-cache names a directory containing
private contents. The former should be an absolute (rooted) directory
name. For example,
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.,
(which is the default value).
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 one other additional user profile, e.g.,
which is created automatically during nmh installation.
$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
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
mhbuild(1), mhl(1), mhlist(1), mhstore(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:
Multipurpose Internet Mail Extensions (MIME) Part Three:
Message Header Extensions for Non-ASCII Text,
Multipurpose Internet Mail Extensions (MIME) Part Four:
Multipurpose Internet Mail Extensions (MIME) Part Five:
Conformance Criteria and Examples.
`+folder' defaults to the current folder
`msgs' defaults to cur
If a folder is given, it will become the current folder. The last mes-
sage selected will become the current message.
[nmh-1.0.4] MH.6.8 MHSHOW(1)
Man(1) output converted with