MHSHOW(1) [nmh-1.0.4] (MH.6.8) MHSHOW(1)
NAME
mhshow - display MIME messages
SYNOPSIS
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]
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 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 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 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 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 specified,
then the display of the message 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 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
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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 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 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 /bin/sh,
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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
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 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 appropriate
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 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 `-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 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:
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
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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. 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, 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.
External Access
For contents of type message/external-body, mhshow supports
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 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 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 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,
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).
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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 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 one other additional user profile,
e.g.,
/usr/freeware/lib/nmh/etc/mhn.defaults
which is created automatically during nmh installation.
FILES
$HOME/.mh_profile The user profile
$MHSHOW Additional profile entries
/usr/freeware/lib/nmh/etc/mhn.defaultSystem default MIME profile entries
/usr/freeware/lib/nmh/etc/mhl.headersThe 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 ALSO
mhbuild(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:
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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.
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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