mh-format(4) Kernel Interfaces Manual mh-format(4)
NAME
mh-format - Format file for the MH message system
DESCRIPTION
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: , f,
,
and . Continuation lines in for-
mat 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
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
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 non-zero (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)Then-Command-String%|Else-Command-String%> %<{component}Then-Command-String%|Else-Com-
mand-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
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.
RESTRICTIONS
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.
EXAMPLES
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: %<(mym-
box{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: %{sub-
ject}%<{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.
RELATED INFORMATION
scan(1), ap(8), dp(8) delim off
mh-format(4)