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📝 NAME

mhl – produce formatted listings of nmh messages

🚀 Quick Reference

Use Case	Command	Description
📄 Display a message with default formatting	mhl message-file	Display one or more message files using the default format file
🎨 Use a custom format file	mhl -form formfile files	Apply a user‑defined format template
📏 Set screen dimensions	mhl -length 50 -width 100	Override terminal height and width (default 40×80)
🔔 Enable bell / clear screen	mhl -bell -clear	Ring terminal bell after each page, clear screen before each page
🔍 Use a different pager	mhl -moreproc /usr/bin/less	Pipe output through an external program (e.g., less)
📂 Use with folder context	mhl -folder +inbox	Set the folder name for the “messagename:” field
🔧 Filter body through a format processor	mhl -fmtproc program	Run message body through an external filter (e.g., for reply quoting)

📋 SYNOPSIS

/usr/lib/mh/mhl [-help] [-version] [-bell | -nobell] [-clear | -nocl\
ear] [-folder +folder] [-form formfile] [-length lines] [-width \
columns] [-moreproc program] [-nomoreproc] [-fmtproc program] \
[-nofmtproc] [files ...]

📖 DESCRIPTION

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 given 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 next, show, 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.

📄 Format File Syntax

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.
• 🔹 A line beginning with “component:” defines the format for the specified component.
• 🔹 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 “***”.

🔧 Variables and Flags

Following are all of the current variables and their arguments. If they follow a component, they apply only to that component, otherwise their effect 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
rtrim	flag	trim whitespace at end of text lines
nortrim	flag	retain whitespace at end of text lines (default)
compress	flag	change newlines in text to spaces
nocompress	flag	don’t compress
wrap	flag	Wrap lines that exceed width (default)
nowrap	flag	Do not perform line wrapping
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
format	flag	Run component through formatproc filter (body only)
noformat	flag	Do not run component through formatproc filter (default)
formatarg	string	Argument to format filter

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).

📋 Ignore and Special Components

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.

📄 Default 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:formatfield="%(unquote(decode{text}))"
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.

The “format” flag specifies that this component will be run through the filter program specified by the formatproc profile entry. This filter program is expected to read data on standard input and output data on standard output. Currently the “format” flag is only supported for the “body” component. The component name will be prefixed to the output after the filter has been run. The expected use of this is to filter a message body to create more pleasing text to use in a reply message. A suggested filter to use for repl(1) is as follows:

body:component=">",overflowtext=">",overflowoffset=0,format,nowrap

The -fmtproc and -nofmtproc switches can be used to override the formatproc profile entry.

The formatarg option specifies a string that is used as an argument to the format filter. This string is processed by mh‑format(5) and all of the message components are available for use. Multiple formatarg options can be used to build up multiple arguments to the format filter.

📁 FILES

• /etc/nmh/mhl.format – The message template
• or <mh-dir>/mhl.format – Rather than the standard template
• $HOME/.mh_profile – The user profile

⚙️ PROFILE COMPONENTS

• moreproc: – Program to use as interactive front‑end
• formatproc: – Program to use as a filter for components that have the “format” flag set.

🔗 SEE ALSO

• show(1)
• ap(8)
• dp(8)

⚙️ DEFAULTS

• -bell
• -noclear
• -length 40
• -width 80

📌 CONTEXT

None

🐛 BUGS

• There should be some way to pass bell and clear information to the front‑end.
• The “nonewline” option interacts badly with “compress” and “split”.
• The “format” option really should work on something other than the body component.

📝 NAME 🚀 Quick Reference 📋 SYNOPSIS 📖 DESCRIPTION 📁 FILES ⚙️ PROFILE COMPONENTS 🔗 SEE ALSO ⚙️ DEFAULTS 📌 CONTEXT 🐛 BUGS