mhl - produce formatted listings of nmh messages

Mhl is an nmh command for filtering and/or displaying text messages. It is the default method of displaying text messages for nmh (it is the default showproc).

As with more, each of the messages specified as arguments (or the standard input) will be output. If more than one message file is specified, the user will be prompted prior to each one, and a <RETURN> or <EOT> will begin the output, with <RETURN> clearing the screen (if appropriate), and <EOT> (usually CTRL-D) suppressing the screen clear. An <INTERRUPT> (usually CTRL-C) will abort the current message output, prompting for the next message (if there is one), and a <QUIT> (usually CTRL-\) will terminate the program (without core dump).

The -bell option tells mhl to ring the terminal's bell at the end of each page, while the -clear option tells mhl to clear the screen at the end of each page (or output a formfeed after each message). Both of these switches (and their inverse counterparts) take effect only if the profile entry moreproc is defined but empty, and mhl is outputting to a terminal. If the moreproc entry is defined and non-empty, and mhl is outputting to a terminal, then mhl will cause the moreproc to be placed between the terminal and mhl and the switches are ignored. Furthermore, if the -clear switch is used and mhl's output is directed to a terminal, then mhl will consult the $TERM and $TERMCAP environment variables to determine the user's terminal type in order to find out how to clear the screen. If the -clear switch is used and mhl's output is not directed to a terminal (e.g., a pipe or a file), then mhl will send a formfeed after each message.

To override the default moreproc and the profile entry, use the -moreproc program switch. Note that mhl will never start a moreproc if invoked on a hardcopy terminal.

The -length length and -width width switches set the screen length and width, respectively. These default to the values indicated by $TERMCAP, if appropriate, otherwise they default to 40 and 80, respectively.

The default format file used by mhl is called “mhl.format”. mhl will first search for this file in the user's nmh directory, and will then search in the directory /etc/nmh. This default can be changed by using the -form formatfile switch.

Finally, the -folder +folder switch sets the nmh folder name, which is used for the “messagename:” field described below. The environment variable $mhfolder is consulted for the default value, which show, next, and prev initialize appropriately.

Mhl operates in two phases: 1) read and parse the format file, and 2) process each message (file). During phase 1, an internal description of the format is produced as a structured list. In phase 2, this list is walked for each message, outputting message information under the format constraints from the format file.

The format file can contain information controlling screen clearing, screen size, wrap-around control, transparent text, component ordering, and component formatting. Also, a list of components to ignore may be specified, and a couple of “special” components are defined to provide added functionality. Message output will be in the order specified by the order in the format file.

Each line of a format file has one of the following forms:

;comment
:cleartext
variable[,variable...]
component:[variable,...]

•

A line beginning with a `;' is a comment, and is ignored.

•

A line beginning with a `:' is clear text, and is output exactly as is.

•

A line containing only a `:' produces a blank line in the output.

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A line beginning with “component:” defines the format for the specified component,

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Remaining lines define the global environment.

For example, the line:

width=80,length=40,clearscreen,overflowtext="***",overflowoffset=5

defines the screen size to be 80 columns by 40 rows, specifies that the screen should be cleared prior to each page, that the overflow indentation is 5, and that overflow text should be flagged with “***”.

Following are all of the current variables and their arguments. If they follow a component, they apply only to that component, otherwise, their affect is global. Since the whole format is parsed before any output processing, the last global switch setting for a variable applies to the whole message if that variable is used in a global context (i.e., bell, clearscreen, width, length).

variable	type	semantics
width	integer	screen width or component width
length	integer	screen length or component length
offset	integer	positions to indent “component: ”
overflowtext	string	text to use at the beginning of an
		overflow line
overflowoffset	integer	positions to indent overflow lines
compwidth	integer	positions to indent component text
		after the first line is output
uppercase	flag	output text of this component in all
		upper case
nouppercase	flag	don't uppercase
clearscreen	flag/G	clear the screen prior to each page
noclearscreen	flag/G	don't clearscreen
bell	flag/G	ring the bell at the end of each page
nobell	flag/G	don't bell
component	string/L	name to use instead of “component” for
		this component
nocomponent	flag	don't output “component: ” for this
		component
center	flag	center component on line (works for
		one-line components only)
nocenter	flag	don't center
leftadjust	flag	strip off leading whitespace on each
		line of text
noleftadjust	flag	don't leftadjust
compress	flag	change newlines in text to spaces
nocompress	flag	don't compress
split	flag	don't combine multiple fields into
		a single field
nosplit	flag	combine multiple fields into
		a single field
newline	flag	print newline at end of components
		(this is the default)
nonewline	flag	don't print newline at end of components
formatfield	string	format string for this component
		(see below)
decode	flag	decode text as RFC-2047 encoded
		header field
addrfield	flag	field contains addresses
datefield	flag	field contains dates

To specify the value of integer-valued and string-valued variables, follow their name with an equals-sign and the value. Integer-valued variables are given decimal values, while string-valued variables are given arbitrary text bracketed by double-quotes. If a value is suffixed by “/G” or “/L”, then its value is useful in a global-only or local-only context (respectively).

A line of the form:

ignores=component,...

specifies a list of components which are never output.

The component “MessageName” (case-insensitive) will output the actual message name (file name) preceded by the folder name if one is specified or found in the environment. The format is identical to that produced by the -header option to show.

The component “Extras” will output all of the components of the message which were not matched by explicit components, or included in the ignore list. If this component is not specified, an ignore list is not needed since all non-specified components will be ignored.

If “nocomponent” is NOT specified, then the component name will be output as it appears in the format file.

The default format file is:

; mhl.format ; ; default message filter for `show' ; : overflowtext="***",overflowoffset=5 leftadjust,compwidth=9 ignores=msgid,message-id,received,content-type,content-transfer-encoding,content-id Date:formatfield="%<(nodate{text})%{text}%|%(pretty{text})%>" To: cc: From:decode Subject:decode : extras:nocomponent : body:nocomponent,overflowtext=,overflowoffset=0,noleftadjust

The variable “formatfield” specifies a format string (see mh-format(5)). The flag variables “addrfield” and “datefield” (which are mutually exclusive), tell mhl to interpret the escapes in the format string as either addresses or dates, respectively.

By default, mhl does not apply any formatting string to fields containing address or dates (see mh-mail(5) for a list of these fields). Note that this results in faster operation since mhl must parse both addresses and dates in order to apply a format string to them. If desired, mhl can be given a default format string for either address or date fields (but not both). To do this, on a global line specify: either the flag addrfield or datefield, along with the appropriate formatfield variable string.

^/etc/nmh/mhl.format~^The message template
^or <mh-dir>/mhl.format~^Rather than the standard template
^$HOME/.mhprofile~^The user profile

^moreproc:~^Program to use as interactive front-end

show(1), ap(8), dp(8)

`-bell'
`-noclear'
`-length40'
`-width80'

None

There should be some way to pass `bell' and `clear' information to the front-end.

The “nonewline” option interacts badly with “compress” and “split”.