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mmh-show(1mh)

MH.6.8
2019-01-06

mmh

set of electronic mail handling programs

NAME

show - display (MIME) messages
next - show the next message
prev - show the previous message

SYNOPSIS

show [+folder] [msgs] [-file file] [-part number] ... [-type content] ... [-form formfile] [-Version] [-help]
next is equivalent to show n
prev is equivalent to show p

NOTE

This (i.e. mmh’s) version of show is a modified version of nmh’s mhshow program. The old (non-MIME) show program was removed from mmh.

DESCRIPTION

The show command display contents of a MIME (multi-media) message or collection of messages. Next and prev perform a show on the next or previous message in the specified (or current) folder, respectively.
show manipulates multi-media messages as specified in RFC-2045 thru RFC-2049. Currently show only supports encodings in message bodies, and does not support the encoding of message headers as specified in RFC-2047.
By default show will display all parts of a multipart message. By using the -part and -type switches, you may limit the scope of show to particular subparts (of a multipart content) and/or particular content types.
The option -file file directs show to use the specified file as the source message, rather than a message from a folder. If you specify this file as ‘-’, then show 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 mh message. It should NOT be in mail drop format (to convert a file in mail drop format to a folder of mh messages, see inc(1)).
When displaying multiple messages, show prepends each of them with a ‘>>> Message nnn’ header, and separates the messages with two lines of space. This is similar to the way mhl acts on multiple files.
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.

Unseen Sequence

If the profile entry ‘Unseen-Sequence’ is present and non-empty, then show will remove each of the messages shown from each sequence named by the profile entry.

Showing the Contents

Mhshow prints messages in a convenient representation. If show is outputting to a terminal, then a pager will be placed between the terminal and show.
The headers of each message are displayed with 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 ‘show’ 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. Similarly, 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 forms:
mhshow-suffix-<type>/<subtype>: <suffix>
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, show 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, show 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:
%l Display listing prior to displaying content
%f Insert filename containing content
%F %f, but stdin is terminal not content
%a Insert parameters from Content-Type field
%s Insert content subtype
%c Insert foreign charset
%d Insert content description
%% The character %
Mhshow processes the MIME parts serially, i.e. the next display process is executed after the previous one has terminated.
Further, when show is display a content, typing QUIT (usually control-\) will tell show 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, show has the following default values:
mhshow-show-text/plain: %liconv -f <source-charset>
mhshow-show-message/rfc822: %lshow -file %F
If a subtype of type text doesn’t have a profile entry, it will be treated as text/plain.
show 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 show 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
When expanding %f and %F escapes, the file names get wrapped in single-quotes automatically.
Finally, show 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. Although a multipart content may contain advice to display the parts in parallel, show will never do so.

Showing Alternate Character Sets

Because a content of type text might be in a non-ASCII character set, when show encounters a ‘charset’ parameter for this content, it checks if your terminal can display this character set natively. show checks this by first examining the the environment variable $MM_CHARSET and if not set, taking the character encoding of the current locale.
If the character set of text/plain cannot be displayed natively, then the default display method converts the content automatically by piping it through:
iconv -f ’<source-charset>’
Note that if you have a custom ‘mhshow-show-*’ display string, you need to care yourself for converting the encodings. (The foreign charset is available through the %c escape.)
The tool iconv needs to be available.
‘mhshow-charset-*’ profile entries are not supported anymore.

Messages of Type message/partial

show 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

Mhshow does not automatically retrieve message/external-body parts (anymore), but prints the relevant information to enable the user to retrieve the files manually.

User Environment

Because the display environment in which show operates may vary for different machines, show 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, show will attempt to consult one other additional user profile, e.g.,
/etc/mmh/mhn.defaults
which is created automatically during mmh installation.

FILES

^$HOME/.mmh/profile~^The user profile
^$MHSHOW~^Additional profile entries
^/etc/mmh/mhn.defaults~^System default MIME profile entries
^/etc/mmh/mhl.headers~^The headers template

PROFILE COMPONENTS

^Path:~^To determine the user’s mail storage
^Current-Folder:~^To find the default current folder
^Unseen-Sequence:~^To name sequences denoting unseen messages
^mhshow-show-<type>*~^Template for displaying contents
^Pager:~^Program to use as interactive front-end

DEFAULTS

+folder’ defaults to the current folder
‘msgs’ defaults to the current message
‘-form mhl.headers’
‘-noverbose

CONTEXT

If a folder is given, it will become the current folder. The last message selected will become the current message.

BUGS

Next and prev are really links to the show program. As a result, if you make a link to next or prev and that link is not called next or prev, your link will act like show instead. To circumvent this, add a profile-entry for the link to your mmh profile and add the argument n or p to the entry.
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