MHSHOW(1)MHSHOW(1)NAMEmhshow - display MIME messages
SYNOPSISmhshow [+folder] [msgs] [-file file] [-part number] ... [-type con‐
tent] ... [-concat | -noconcat] [-textonly | -notextonly] [-inli‐
neonly | -noinlineonly] [-form formfile] [-markform 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 to 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 only text parts of a message that are
not marked as attachments. This behavior can be changed by the -notex‐
tonly and -noinlineonly switches. In addition, by using the -part and
-type switches, you may further limit the scope of mhshow to particular
subparts (of a multipart content) and/or particular content types. The
inclusion of any -part or -type switches will override the default set‐
tings of -textonly and -inlineonly.
By default mhshow will concatenate all content under one pager. If you
which each part to displayed separately, you can override the default
behavior with -noconcat.
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:
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 mes‐
sage/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 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
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 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:
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 stan‐
dard input set to the content.
The display string may contain the following escapes:
%a Insert parameters from Content-Type field
%{parameter} Insert the parameter value from the Content-Type field
%f Insert filename containing content
%F %f, and stdin is terminal not content
%l display listing prior to displaying content
%s Insert content subtype
%d Insert content description
%% Insert the character %
Mhshow will execute at most one display string at any given time, and
wait for the current display string to finish execution before execut‐
ing the next display string.
The {parameter} escape is typically used in a command line argument
that should only be present if it has a non-null value. Its value will
be wrapped with single quotes if the escape is not so wrapped. Shell
parameter expansion can construct the argument only when it is non-
null, e.g.,
mhshow-show-text/html: charset=%{charset};
w3m ${charset:+-I $charset} -T text/html %F
That example also shows the use of indentation to signify continuation:
the two text lines combine to form a single entry. Note that when
dealing with text that has been converted internally by iconv(3), the
“charset” parameter will reflect the target character set of the text,
rather than the original character set in the message.
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 behaves as if these profile
entries were supplied and supported:
mhshow-show-text/plain: %lmoreproc %F
mhshow-show-message/rfc822: %lshow -file %F
Note that “moreproc” is not supported in user profile display strings.
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‐
part/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 com‐
plain.
Example entries might be:
mhshow-show-audio/basic: raw2audio 2>/dev/null | play
mhshow-show-image: xv %f
mhshow-show-application/PostScript: lpr -Pps
If an f- or F-escape is not quoted with single quotes, its expansion
will be wrapped with single quotes.
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.
Showing Alternate Character Sets
If mhshow was built with iconv(3), then all text/plain parts of the
message(s) will be displayed using the character set of the current
locale. See the mhparam(1) man page for how determine whether your nmh
installation includes iconv(3) support. To convert text parts other
than text/plain, or if mhshow was not built with iconv, an external
program can be used, as described next.
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.
mhshow checks this by examining the current character set defined by
the locale(1) environment variables. If the value of the locale char‐
acter set is equal to the value of the charset parameter, then mhshow
assumes it can display this content without any additional setup. If
the locale is not set properly, 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-nor‐
mal-*-*-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. For example, messages
encoded in the ISO-8859-1 character set can be view using less, with
these environment variable settings:
LESSCHARSET latin1
LESS -f
The first setting tells less to use the ISO-8859-1 definition for
determining whether a character is “normal”, “control“, or “binary”.
The second setting 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
· url
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.
For the “url” access-type, mhshow will look for the “nmh-access-url”
profile entry. See mhstore(1) for more details.
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-acces‐
sible 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 particu‐
lar 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
/usr/local/etc/nmh/mhn.defaults
which is created automatically during nmh installation.
See "Profile Lookup" in mh-profile(5) for the profile search order, and
for how duplicate entries are treated.
Content-Type Marker
If mhshow decides to not display a particular part due to the switches
of -textonly or -inlineonly it will display a marker containing infor‐
mation about the part. This marker is processed via mh-format(5) and
can be changed by the use of the -markform switch to specify a file
containing the mh-format(5) instructions to use when displaying the
content marker. In addition to the normal set of mh-format(5) instruc‐
tions, the following component escapes are supported:
Escape Returns Description
part string MIME part number
content-type string MIME Content-Type of part
description string Content-Description header
disposition string Content disposition (attachment or inline)
ctype-<PARAM> string Value of <PARAM> from Content-Type header
cdispo-<PARAM> string Value of <PARAM> from
Content-Disposition header
All MIME parameters and the “Content-Description” header will have RFC
2231 decoding applied and be converted to the local character set.
FILESmhshow looks for all format files and mhn.defaults in multiple loca‐
tions: absolute pathnames are accessed directly, tilde expansion is
done on usernames, and files are searched for in the user's Mail direc‐
tory as specified in their profile. If not found there, the directory
“/usr/local/etc/nmh” is checked.
$HOME/.mh_profile The user profile
$MHSHOW Additional profile entries
/usr/local/etc/nmh/mhn.defaults System default MIME profile entries
/usr/local/etc/nmh/mhl.headers The headers template
/usr/local/etc/nmh/mhshow.marker Example content marker
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-access-url: Program to retrieve contents via HTTP
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 ALSOiconv(3), mhbuild(1), mhl(1), mhlist(1), mhparam(1), mhstore(1), send‐
files(1)DEFAULTS
`+folder' defaults to the current folder
`msgs' defaults to cur
`-nocheck'
`-concat'
`-textonly'
`-inlineonly'
`-form mhl.headers'
`-rcache ask'
`-wcache ask'
CONTEXT
If a folder is given, it will become the current folder. The last mes‐
sage selected will become the current message.
nmh-1.6 April 9, 2014 MHSHOW(1)
