mh-format - Format file for the MH message system
Several MH commands utilize either a format string or a
format file during their execution. For example, scan(1)
uses a format string which specifies how scan should 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.
This reference page describes how to write new format commands
or modify existing ones. You should not attempt
this unless you are an experienced MH user.
A format string is similar to a printf string, but uses
multi-letter escapes. The rest of this reference page
assumes a knowledge of the printf routine. When specifying
a 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.
When an escape is interpreted and the result is immediately
printed, you can specify an optional field width to
print the field in exactly a given number of characters.
A numeric escape, such as "%4(size)", will print at most 4
digits of the value. Any overflow is marked by a ? in the
first position, for example ?123. A string escape, such as
"%4(me)", will print the first four characters of the
string. In both cases, short fields are padded at the
right, usually with a blank. If the field width argument
begins with a zero, for example "%04(size)", the fill
character is a zero.
The interpretation model is based on a simple machine with
two registers, num and str. The former contains an integer
value, the latter a string value. When an escape is
processed, if it requires an argument, it reads the current
value of either num or str; and, if it returns a
value, it writes either num or str.
Escapes are of three types: components, functions, and
control.
Component Escapes [Toc] [Back]
A component escape represents a header field in the message
being processed. It is written {name}, where the
name is the name of the header field. For example, {date}
refers to the Date: field of the message.
The value of a component escape is the content of the
named field. This is always a string. For example, the
header of an unsent message might look as follows: To:
smith@local cc: davis Subject: tomorrow's meeting In this
example, the value of the component escape {subject} is
the string "tomorrow's meeting".
Control Escapes [Toc] [Back]
A control escape is one of: %<, %| and %>. These correspond
to if-then-else constructs.
There are two syntaxes allowed by these control escapes.
The first is: %<(function)Command-string%> %<{component}Command-String%>
If the function or component is nonzero
(for integer-valued escapes) or non-empty (for
string-valued escapes), everything up to the corresponding
%> is interpreted. Otherwise, skip to the next %> and
begin interpreting again.
The second form of syntax is as follows: %<(function)ThenCommand-String%|Else-Command-String%>
%<{component}ThenCommand-String%|Else-Command-String%>
If the function or
component is non-zero or non-null, the Then-Command-String
is interpreted. Otherwise, skip to %| and interpret the
Else-Command-String. Only one string is ever interpreted;
if the first string is interpreted, the system skips from
the %| control escape to the %> character.
Function Escapes [Toc] [Back]
A function escape is specified as %(name), and is statically
defined.
Most functions expect an argument of a particular type.
In the tables of functions that follow, these types are
referred to:
literal A literal number or string; for example, %(func
1234) takes the number 1234 as its argument.
comp Any header component; for example, %(func{from})
takes the contents of the From: header field as
an argument.
expr An optional component, function or string, perhaps
nested. For example, %(func (func2{comp}))
takes the return value of the function
(func2{comp}) as its argument. If no argument
is provided, the function will read either the
num or the str register, as appropriate.
Functions return three types of values: string, integer,
and, for those functions which return a true or false status,
boolean. In the tables that follow, str and num represent
the values stored in these registers. arg represents
the value of the argument supplied to the function.
The following table lists the function escapes:
-------------------------------------------------------------------
Escape Argument Returns Interpretation
-------------------------------------------------------------------
msg integer message number
cur integer message is current
size integer size of message
strlen integer length of str
width integer output buffer size in bytes
charleft integer integer space left in output buffer
timenow integer seconds since the epoch
me string the user's mailbox
eq literal integer num == arg
ne literal integer num != arg
gt literal integer num > arg
match literal boolean str contains arg
amatch literal boolean str starts with arg
plus integer arg plus num
minus integer arg minus num
divide literal integer num divided by arg
num literal integer Set num to arg
lit literal integer Set str to arg
nonzero expr integer num is non-zero
zero expr integer num is zero
null expr integer str is empty
nonnull expr integer str is non-empty
void expr Set str or num
comp comp string Set str to component text
compval comp integer num set to atoi(str)
trim expr trim trailing white space from str
putstr expr print str
putstrf expr print str in a fixed width
putnum expr print num
putnum expr print num in a fixed width
-------------------------------------------------------------------
The following functions require a date component as an
argument:
-------------------------------------------------------------------------
Escape Argument Returns Interpretation
-------------------------------------------------------------------------
sec date integer seconds of the minute
min date integer minutes of the day
hour date integer hours of the day (24 hour clock)
wday date integer day of the week (Sunday=0)
day date string day of the week
weekday date string day of the week (long)
sday date integer day of the week known
1 for explicit in date
0 for implicit
-1 for 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 (abbreviated)
lmonth date string month of the year (long form)
year date integer year of the century
zone date integer timezone in hours
tzone date string timezone as a string
szone date integer timezone explicit?
1 for explicit
0 for implicit
-1 for 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 epoch
rclock date integer seconds prior to current time
tws date string official RFC 822 rendering of the date
pretty date string a more user-friendly rendering
nodate date str could not be parsed as a date
-------------------------------------------------------------------------
The following functions require an address component as an
argument. Some functions return a value based on the
first address in the field only. These are indicated by
the note (first only).
-----------------------------------------------------------------------
Escape Argument Returns Interpretation
-----------------------------------------------------------------------
proper addr string official RFC 822 rendering
of the address
friendly string string a more user-friendly
rendering
pers addr string the personal name (first only)
note addr string commentary text (first only)
mbox addr string the local part of the address
(first only)
mymbox addr does the address refer to
the user's mailbox?
(0=no, 1=yes)
host addr string the domain part of the address
(first only)
nohost addr integer no host was present in the address
(first only)
type addr integer the type of host
-1 for uucp
0 for local
1 for network
2 for unknown
path addr string the route part of the address
(first only)
ingrp addr integer the address appeared inside a group
(first only)
gname addr string name of the group (first only)
formataddr expr append arg to str as
an address list
putaddr literal print str address list with arg
as an optional label; get line width
from num
-----------------------------------------------------------------------
Some functions that print their arguments can be controlled
by giving field width arguments. The functions
(putnumf) and (putstrf) print their arguments as specified
by the field width arguments. So %06(putnumf(size)) will
print the message size in six digits, filled with leading
zeros; %14(putsrtf{from}) will print the From: header
field in 14 characters, with trailing spaces as required.
With (putstrf), supplying a negative field width will
cause the string to be right-justified within the field.
The functions (putnum) and (putstr) ignore any field width
arguments, and print their arguments in the minimum number
of characters required.
When the friendly format for addresses is used, addresses
longer than about 180 characters are truncated to an empty
string. This means that such addresses will not appear in
the scan display.
The function (mymbox{comp}) checks each of the addresses
in the named header component {comp} against the user's
mailbox name, and against any other mailboxes listed in
the Alternate-Mailboxes entry in the user's .mh_profile.
It returns true if any of the address matches. However,
it also returns true if the named {comp} header field is
not present. If necessary, you can use the (null) or (nonnull)
functions to test explicitly for the presence of the
field.
The default format string for scan follows. This has been
divided into several pieces for readability. The first
part is: %4(msg)%<(cur)+%| %>%<{replied}-%| %> This means
that the message number should be printed in four digits;
if the message is the current message then a + is printed.
If the message is not the current message, then a space is
printed. If a Replied: field is present, a - is printed.
If no Replied: field is present, then a space is printed.
Next: %02(mon{date})/%02(mday{date}) The month and date
are printed in two digits (zero filled). Next: %<{date}
%|*> If no Date: field is present, then a * is printed,
otherwise a space. Next: %<(mymbox{from})To:%14(friendly{to})
If the message is from me,
print To: followed by a user-friendly rendering of the
first address in the To: field. %|%17(friendly{from})%>
If the message is not from me, then the From: address is
printed. And finally: %{subject}%<{body}<<%{body}%> The
subject and initial body are printed preceded by the
string <<.
Although this seems complicated, this method is flexible
enough to extract individual fields and print them in any
format the user desires.
If the -form formatfile switch is given with the scan command,
it will treat each line in the named file as a format
string, and act accordingly. This lets the user
develop template scan listing formats. Some examples can
be found in /usr/lib/mh/scan.time, /usr/lib/mh/scan.size,
and /usr/lib/mh/scan.timely.
scan(1), ap(8), dp(8) delim off
mh-format(4)
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