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.
• 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 ``***''.

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
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).

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.

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.