mhn -list (for MH) and mhlist (for nmh-1.0 and above) summarize the contents of MIME messages. The output has five columns: message number, message part number, content-type and subtype, size in octets (which are basically bytes or us-ascii characters), and content-description (if any). If you don't give message numbers, the current message is listed. For example, here's how to list the current and next messages (message numbers 33 and 34):
% mhn -list cur next
msg part type/subtype size description
33 multipart/mixed 44K
1 text/plain 1459 Description of picture
2 image/x-pbm 40K Picture of front panel
34 multipart/alternative 2914
1 multipart/mixed 1688
1.1 text/enriched 481
1.2 message/external-body 69 "Louie Louie"
audio/basic
1.3 message/external-body 67 Cruisers at Park concert
image/gif
2 text/plain 817
Message 33 has multipart/mixed content. The total size is
approximately 44,000 octets. The first part is text/plain,
1459 octets, with a Content-description: of "Description
of picture." Part 2 is an image in the nonstandard content
subtype x-pbm. (Although x-pbm means that
the pbm format isn't an official MIME type registered with
the IANA, it's widely used.) The total size of 44k is the sum of
the parts, after decoding, plus the other header fields.
Message 34 has the content-type multipart/alternative. This means that either part 1 or part 2 will be shown. Note that mhn and mhlist don't necessarily list the parts of a multipart/alternative message in the same order they appear in the message. The alternatives are listed in descending priority. The MIME specification says that the "simplest" (closest to plain text) part should be first in the body; this lets people without MIME-capable MUAs make some sense of the message.
Message 34 has three subparts: text/enriched, message/external-body (which, if you retrieve it, will have audio/basic content), and another message/external-body part (this one with image/gif content). Notice that the body parts' sizes are small (69 and 67 characters). That's because they're external parts that haven't been retrieved yet.
To list only one part of a message, if you know the part number, you can call mhlist -part or mhn -list -part followed by the part number. Or, if you know the content type of the part(s) you want to see, use mhlist -type or mhn -type.
mhn -list and mhlist will show you any comments and parameters from the Content-Type: field if you use the -verbose switch. Compare this listing of message 33 to the one above:
% mhn -list -verbose
msg part type/subtype size description
33 multipart/mixed 44K
1 text/plain 1459 Description of picture
(sorry; I wrote this in a hurry)
2 image/x-pbm 40K Picture of front panel
x-density="75 dpi"
By default, each body part is decoded before
its size is checked. That isn't necessarily the size a body part
has in the message. For example, in a message with base64
encoding, each four encoded characters (like LnNu) are
decoded to three octets (8-bit bytes). If you add
the -norealsize switch, mhn -list and mhlist
will give you the encoded size of body parts. For long
messages, -norealsize can save time, too, because the parts
don't have to be decoded before their sizes are computed.
Sometimes I wish that mhn -list and mhlist would show the message Subject:, too. The little shell function called mscan, below, runs scan to show the subject, followed by mhn -list to show the contents. (nmh users: you can use mhlist instead.) It defaults to the current message, but you also can give it folder or message arguments.
mscan() { scan ${*-cur} && mhn -list $* ; }
The Bourne-type shell parameter substitution
operator, ${*-cur}, passes scan the message
name cur if you run mscan with no arguments.
(Otherwise, scan would scan all messages: not what we want
here!) By default, mhn -list displays the current message;
and, luckily, the shell ignores $* if there were no
arguments. This is hard to write concisely in a C shell alias; if
you use csh, you can make it into a
one-line shell script. Here's an mscan of the current
message:
$ mscan
53+ 05/18 To:Maree Winkler Messages from Jon about next week's meeting
msg part type/subtype size description
53 multipart/mixed 12K
1 text/plain 434
2 multipart/digest 8095 forwarded messages
2.1 message/rfc822 4293
2.2 message/rfc822 2491