Provided by: nmh_1.5-release-5_amd64 
NAME
mhshow - display MIME messages
SYNOPSIS
mhshow [+folder] [msgs] [-file file] [-part number] ... [-type content] ... [-serialonly
| -noserialonly] [-pause | -nopause] [-form formfile] [-rcache policy] [-wcache
policy] [-check | -nocheck] [-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 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 is 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 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”, 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.
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 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(1) 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 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.
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).
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.,
/etc/nmh/mhn.defaults
which is created automatically during nmh installation.
FILES
$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
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-<charsTe>mplate 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)
DEFAULTS
`+folder' defaults to the current folder
`msgs' defaults to cur
`-nocheck'
`-form mhl.headers'
`-pause'
`-rcache ask'
`-noserialonly'
`-wcache ask'
CONTEXT
If a folder is given, it will become the current folder. The last message selected will
become the current message.