Computer Science
MH-FORMAT(5) MH-FORMAT(5)
NAME
mh-format - format file for nmh message system
SYNOPSIS
some nmh commands
DESCRIPTION
Several nmh commands utilize either a format string or a
format file during their execution. For example, scan (1)
uses a format string which directs it how to generate the
scan listing for each message; repl (1) uses a format file
which directs it how to generate the reply to a message,
and so on.
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 compo-
nents, built-in functions, and flow control.
A component escape is specified as `%{component}', and
exists for each header found in the message being pro-
cessed. 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 interpreta-
tions 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 con-
struct:
%<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 compo-
nent 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; nor-
mal 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 inter-
preted. If the control escape encountered was `%?', then
the condition associated with that control escape is eval-
uated, 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 argu-
ments.
The evaluation of format strings is based on a simple vir-
tual 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 pre-
sent, 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 argu-
ment. The return value of functions noted with `*' per-
tain only to the first address present in the header com-
ponent.
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 charac-
ter (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 regis-
ter; 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 read-
ability. 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 pre-
sent. 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})%(for-
mataddr(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 out-
put.
%<{subject}Subject: Re: %{subject}\n%>\
If a subject component was present, a suitable reply sub-
ject 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 for-
mat, 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 elabo-
ration. 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
[nmh-0.27] MH.6.8 1
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