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mh-format - format file for nmh message system
Format strings are designed to be efficiently parsed by nmh which means they are not necessarily simple to write and understand. This means that novice, casual, or even advanced users of nmh should not have to deal with them.
There are a few alternate scan listing formats available in /etc/nmh/scan.time, /etc/nmh/scan.size, and /etc/nmh/scan.timely. Look in /etc/nmh for other scan and repl format files which may have been written at your site.
It suffices to have your local nmh expert actually write new format commands or modify existing ones. This manual section explains how to do that. Note: familiarity with the C printf routine is assumed.
A format string consists of ordinary text, and special multi-character escape sequences which begin with `%'. When specifying a format string, the usual C backslash characters are honored: `\b', `\f', `\n', `\r', and `\t'. Continuation lines in format files end with `\' followed by the newline character.
There are three types of escape sequences: header components, built-in functions, and flow control.
A component escape is specified as `%{component}', and exists for each header found in the message being processed. For example `%{date}' refers to the ``Date:'' field of the appropriate message. All component escapes have a string value. Normally, component values are compressed by converting any control characters (tab and newline included) to spaces, then eliding any leading or multiple spaces. However, commands may give different interpretations to some component escapes; be sure to refer to each command's manual entry for complete details.
A function escape is specified as `%(function)'. All functions are built-in, and most have a string or numeric value.
A control escape is one of: `%<', `%?', `%|', or `%>'. These are combined into the conditional execution construct:
%<condition
format text 1
%?condition2
format text 2
%?condition3
format text 3
...
%|
format text N
%>
Extra white space is shown here only for clarity. These constructs may be nested without ambiguity. They form a general if-elseif-else-endif block where only one of the format text segments is interpreted.
The `%<' and `%?' control escapes causes a condition to be evaluated. This condition may be either a component or a function. The four constructs have the following syntax:
%<{component}
%<(function)
%?{component}
%?(function)
These control escapes test whether the function or component value is non-zero (for integer-valued escapes), or non-empty (for string-valued escapes).
If this test evaulates true, then the format text up to the next corresponding control escape (one of `%|', `%?', or `%>') is interpreted normally. Next, all format text (if any) up to the corresponding `%>' control escape is skipped. The `%>' control escape is not interpreted; normal interpretation resumes after the `%>' escape.
If the test evaluates false, however, then the format text up to the next corresponding control escape (again, one of `%|', `%?', or `%>') is skipped, instead of being interpreted. If the control escape encountered was `%?', then the condition associated with that control escape is evaluated, and interpretation proceeds after that test as described in the previous paragraph. If the control escape encountered was `%|', then the format text up to the corresponding `%>' escape is interpreted normally. As above, the `%>' escape is not interpreted and normal interpretation resumes after the `%>' escape.
The `%?' control escape and its following format text is optional, and may be included zero or more times. The `%|' control escape and its following format text is also optional, and may be included zero or one times.
Most functions expect an argument of a particular type:
Argument Description Example Syntax
literal A literal number, %(func 1234)
or string %(func text string)
comp Any header component %(func{in-reply-to})
date A date component %(func{date})
addr An address component %(func{from})
expr An optional component, %(func(func2))
function or control, %(func %<{reply-to}%|%{from}%>)
perhaps nested %(func(func2{comp}))
The types date and addr have the same syntax as comp, but require that the header component be a date string, or address string, respectively.
All arguments except those of type expr are required. For the expr argument type, the leading `%' must be omitted for component and function escape arguments, and must be present (with a leading space) for control escape arguments.
The evaluation of format strings is based on a simple virtual machine with an integer register num, and a text string register str. When a function escape is processed, if it accepts an optional expr argument which is not present, it reads the current value of either num or str as appropriate.
Component escapes write the value of their message header in str. Function escapes write their return value in num for functions returning integer or boolean values, and in str for functions returning string values. (The boolean type is a subset of integers with usual values 0=false and 1=true.) Control escapes return a boolean value, and set num.
All component escapes, and those function escapes which return an integer or string value, pass this value back to their caller in addition to setting str or num. These escapes will print out this value unless called as part of an argument to another escape sequence. Escapes which return a boolean value do pass this value back to their caller in num, but will never print out the value.
Function Argument Return Description msg integer message number cur integer message is current unseen integer message is unseen size integer size of message strlen integer length of str width integer output buffer size in bytes charleft integer bytes left in output buffer timenow integer seconds since the UNIX epoch me string the user's mailbox eq literal boolean num == arg ne literal boolean num != arg gt literal boolean num > arg match literal boolean str contains arg amatch literal boolean str starts with arg plus literal integer arg plus num minus literal integer arg minus num divide literal integer num divided by arg modulo literal integer num modulo arg num literal integer Set num to arg lit literal string Set str to arg getenv literal string Set str to environment value of arg profile literal string Set str to profile component arg value nonzero expr boolean num is non-zero zero expr boolean num is zero null expr boolean str is empty nonnull expr boolean str is non-empty void expr Set str or num comp comp string Set str to component text compval comp integer Set num to ``atoi(comp)'' decode expr string decode str as RFC-2047 component trim expr trim trailing white-space from str putstr expr print str putstrf expr print str in a fixed width putnum expr print num putnumf expr print num in a fixed width
These functions require a date component as an argument:
Function Argument Return Description
sec date integer seconds of the minute
min date integer minutes of the hour
hour date integer hours of the day (0-23)
wday date integer day of the week (Sun=0)
day date string day of the week (abbrev.)
weekday date string day of the week
sday date integer day of the week known?
(0=implicit,-1=unknown)
mday date integer day of the month
yday date integer day of the year
mon date integer month of the year
month date string month of the year (abbrev.)
lmonth date string month of the year
year date integer year (may be > 100)
zone date integer timezone in hours
tzone date string timezone string
szone date integer timezone explicit?
(0=implicit,-1=unknown)
date2local date coerce date to local timezone
date2gmt date coerce date to GMT
dst date integer daylight savings in effect?
clock date integer seconds since the UNIX epoch
rclock date integer seconds prior to current time
tws date string official 822 rendering
pretty date string user-friendly rendering
nodate date integer str not a date string
These functions require an address component as an argument. The return value of functions noted with `*' pertain only to the first address present in the header component.
Function Argument Return Description
proper addr string official 822 rendering
friendly addr string user-friendly rendering
addr addr string mbox@host or host!mbox rendering*
pers addr string the personal name*
note addr string commentary text*
mbox addr string the local mailbox*
mymbox addr integer the user's addresses? (0=no,1=yes)
host addr string the host domain*
nohost addr integer no host was present*
type addr integer host type* (0=local,1=network,
-1=uucp,2=unknown)
path addr string any leading host route*
ingrp addr integer address was inside a group*
gname addr string name of group*
formataddr expr append arg to str as a
(comma separated) address list
putaddr literal print str address list with
arg as optional label;
get line width from num
When escapes are nested, evaluation is done from inner-most to outer-most. The outer-most escape must begin with `%'; the inner escapes must not. For example,
%<(mymbox{from}) To: %{to}%>
writes the value of the header component ``From:'' to str; then (mymbox) reads str and writes its result to num; then the control escape evaluates num. If num is non-zero, the string ``To: '' is printed followed by the value of the header component ``To:''.
A minor explanation of (mymbox{comp}) is in order. In general, it checks each of the addresses in the header component ``comp'' against the user's mailbox name and any Alternate-Mailboxes. It returns true if any address matches, however, it also returns true if the ``comp'' header is not present in the message. If needed, the (null) function can be used to explicitly test for this condition.
When a function or component escape is interpreted and the result will be immediately printed, an optional field width can be specified to print the field in exactly a given number of characters. For example, a numeric escape like %4(size) will print at most 4 digits of the message size; overflow will be indicated by a `?' in the first position (like `?234'). A string escape like %4(me) will print the first 4 characters and truncate at the end. Short fields are padded at the right with the fill character (normally, a blank). If the field width argument begins with a leading zero, then the fill character is set to a zero.
As above, the functions (putnumf) and (putstrf) print their result in exactly the number of characters specified by their leading field width argument. For example, %06(putnumf(size)) will print the message size in a field six characters wide filled with leading zeros; %14(putstrf{from}) will print the ``From:'' header component in fourteen characters with trailing spaces added as needed. For putstrf, using a negative value for the field width causes right-justification of the string within the field, with padding on the left up to the field width. The functions (putnum) and (putstr) print their result in the minimum number of characters required, and ignore any leading field width argument.
The available output width is kept in an internal register; any output past this width will be truncated.
Comments may be inserted in most places where a function argument is not expected. A comment begins with `%;' and ends with a (non-escaped) newline.
With all this in mind, here's the default format string for scan. It's been divided into several pieces for readability. The first part is:
%4(msg)%<(cur)+%| %>%<{replied}-%?{encrypted}E%| %>
which says that the message number should be printed in four digits, if the message is the current message then a `+' else a space should be printed, and if a ``Replied:'' field is present then a `-' else if an ``Encrypted:'' field is present then an `E' otherwise a space should be printed. Next:
%02(mon{date})/%02(mday{date})
the month and date are printed in two digits (zero filled) separated by a slash. Next,
%<{date} %|*>
If a ``Date:'' field was present, then a space is printed, otherwise a `*'. Next,
%<(mymbox{from})%<{to}To:%14(friendly{to})%>%>
if the message is from me, and there is a ``To:'' header, print `To:' followed by a ``user-friendly'' rendering of the first address in the ``To:'' field. Continuing,
%<(zero)%17(friendly{from})%>
if either of the above two tests failed, then the ``From:'' address is printed in a ``user-friendly'' format. And finally,
%{subject}%<{body}<<%{body}%>
the subject and initial body (if any) are printed.
For a more complicated example, next consider the default replcomps format file.
%(lit)%(formataddr %<{reply-to}
This clears str and formats the ``Reply-To:'' header if present. If not present, the else-if clause is executed.
%?{from}%?{sender}%?{return-path}%>)\
This formats the ``From:'', ``Sender:'' and ``Return-Path:'' headers, stopping as soon as one of them is present. Next:
%<(nonnull)%(void(width))%(putaddr To: )\n%>\
If the formataddr result is non-null, it is printed as an address (with line folding if needed) in a field width wide with a leading label of ``To: ''.
%(lit)%(formataddr{to})%(formataddr{cc})%(formataddr(me))\
str is cleared, and the ``To:'' and ``Cc:'' headers, along with the user's address (depending on what was specified with the ``-cc'' switch to repl) are formatted.
%<(nonnull)%(void(width))%(putaddr cc: )\n%>\
If the result is non-null, it is printed as above with a leading label of ``cc: ''.
%<{fcc}Fcc: %{fcc}\n%>\
If a ``-fcc folder'' switch was given to repl (see repl (1) for more details about %{fcc}), an ``Fcc:'' header is output.
%<{subject}Subject: Re: %{subject}\n%>\
If a subject component was present, a suitable reply subject is output.
%<{date}In-reply-to: Your message of "\
%<(nodate{date})%{date}%|%(pretty{date})%>."%<{message-id}
%{message-id}%>\n%>\
--------
If a date component was present, an ``In-Reply-To:'' header is output with the preface ``Your message of ''. If the date was parseable, it is output in a user-friendly format, otherwise it is output as-is. The message-id is included if present. As with all plain-text, the row of dashes are output as-is.
This last part is a good example for a little more elaboration. Here's that part again in pseudo-code:
if (comp_exists(date)) then
print (``In-reply-to: Your message of \``'')
if (not_date_string(date.value) then
print (date.value)
else
print (pretty(date.value))
endif
print (``\'''')
if (comp_exists(message-id)) then
print (``\n\t'')
print (message-id.value)
endif
print (``\n'')
endif
Although this seems complicated, in point of fact, this method is flexible enough to extract individual fields and print them in any format the user desires. None None scan(1), repl(1), ap(8), dp(8) None None
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