Bart Massey submitted an update to the mh-format man page as part of
bug report 2031. I'm not an expert on the content, but it looks like
he's done a good job at improving this page.
Please review it, and if there are no corrections, I plan to commit it.
Thanks.
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
uses a format string which directs it how to generate the
scan listing for each message; repl 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 escapesequences 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.
SYNTAX
Format strings are built around escape sequences. There
are three types of escape sequences: header components,
built-in functions, and flow control. 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.
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 function escape may have an argument. The argu-
ment follows the function escape: separating whitespace is
discarded: `%(function argument)'.
The argument to a function escape is processed in argument
mode. A function or component escape evaluated in argu-
ment mode should not be preceded by a leading `%'. Condi-
tional escapes (see below) are allowed, and are entered
normally.
Control-flow escapes
A control escape is one of: `%<', `%?', `%|', or `%>'.
These are combined into the conditional execution con-
struct:
%< condition format-text
%? condition format-text
...
%| format-text
%>
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-texts is interpreted.
A `%<' or `%?' control escape causes its condition to be
evaluated. This condition is a component or function
escape evaluated in argument mode. The control escape
tests whether the function or component escape evaluates
non-zero (for an integer-valued escape) or non-empty (for
a string-valued escape).
If the condition of a `%<' or `%?' control escape
evaulates true, or a `%|' escape is encountered, then the
format-text of that escape (up to the next corresponding
`%|', `%?', or `%>' control escape) is interpreted nor-
mally. Text up to the corresponding `%>' control escape is
then skipped, and the `%>' control escape is discarded.
If the condition of a `%<' or `%?' control escape evalu-
ates false, however, the format-text (up to the next cor-
responding `%|', `%?', or `%>' control escape) is skipped
instead of being interpreted. Evaluation then continues
at the new escape.
The `%?' control escape is optional, and may be included
zero or more times. The `%|' control escape is also
optional, and may be included at most once.
Function escapes
Functions expecting an argument generally require an argu-
ment of a particular type. In addition to the number and
string types, these include:
Argument Description Example Syntax
literal A literal number %(func 1234)
or string %(func text string)
comp Any component %(func{in-reply-to})
date A date component %(func{date})
addr An address component %(func{from})
expr Nothing %(func)
or a subexpression %(func(func2))
or control escape %(func %<{reply-to}%|%{from}%>)
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.
Most arguments not of type expr are required. When
escapes are nested (via expr arguments), evaluation is
done from inner-most to outer-most. As noted above, for
the expr argument type, the evaluation is performed in
argument mode: the leading `%' must be omitted for compo-
nent and function escape arguments, and must be present
(with a leading space) for control escape arguments. 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:".
Evaluation
The evaluation of format strings is performed by a small
virtual machine. The machine is capable of evaluating
nested expressions as described above, and in addition has
an integer register num, and a text string register str.
When a function escape that accepts an optional argument
is processed, and the argument is not present, the current
value of either num or str is used as the argument: which
register is used depends on the function, as listed below.
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, setting
num to 1 if the last explicit condition evaluated by a
`%<' or `%?' control succeeded, and 0 otherwise.
All component escapes, and those function escapes which
return an integer or string value, evaluate to their value
as well as setting str or num. Outermost escape expres-
sions in these forms will print their value, but outermost
escapes which return a boolean value do not result in
printed output.
Functions
The function escapes may be roughly grouped into a few
categories.
Function Argument Result Description
msg integer message number
cur integer message is current (0 or 1)
unseen integer message is unseen (0 or 1)
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.
num integer Set num to zero.
lit literal string Set str to arg.
lit string Clear str.
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 (MIME-encoded)
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
nodate string integer Argument not a date string (0 or 1)
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
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?
(1=explicit,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?
(1=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? (0 or 1)
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
These functions require an address component as an argu-
ment. The return value of functions noted with `*' is
computed from 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 [EMAIL PROTECTED] or host!mbox rendering*
pers addr string the personal name*
note addr string commentary text*
mbox addr string the local mailbox*
mymbox addr integer List has the user's address? (0 or 1)
host addr string the host domain*
nohost addr integer no host was present (0 or 1)*
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 (0 or 1)*
gname addr string name of group*
(A clarification on (mymbox{comp}) is in order. This
function checks each of the addresses in the header compo-
nent "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
case.)
Formatting
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.
The functions (putnumf) and (putstrf) print their result
in exactly the number of characters specified by their
leading field width argument. For example, %06(put-
numf(size)) will print the message size in a field six
characters wide filled with leading zeros; %14(put-
strf{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 func-
tions (putnum) and (putstr) are somewhat special: they
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.
Examples
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; 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})%(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 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
One more example: Currently, nmh supports very large mes-
sage numbers, and it is not uncommon for a folder to have
far more than 10000 messages. Nontheless (as noted above)
the various scan format strings are inherited from older
MH versions, and are generally hard-coded to 4 digits of
message number before formatting problems start to occur.
The nmh format strings can be modified to behave more sen-
sibly with larger message numbers:
%(void(msg))%<(gt 9999)%(msg)%|%4(msg)%>
The current message number is placed in num. (Note that
(msg) is an int function, not a component.) The (gt) con-
ditional is used to test whether the message number has 5
or more digits. If so, it is printed at full width: oth-
erwise at 4 digits.
See Also
scan(1), repl(1), ap(8), dp(8)
Context
None
