mh-format - format file for nmh message system
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.
There are a few alternate scan listing formats available in
nmh/etc/scan.time,
nmh/etc/scan.size, and
nmh/etc/scan.timely. Look in
nmh/etc 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.
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 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. Some commands (such as
ap and
mhl) use a special component `%{
text}' to refer to
the text being processed; see their respective man pages for details and
examples.
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 argument follows the function escape: separating
whitespace is discarded: `%(
function argument)'.
In addition to literal numbers or strings, the argument to a function escape can
be another function, a component, or a control escape. When the argument is a
function or a component, they are listed without a leading `%'. When control
escapes are used as function arguments, they written as normally, with a
leading `%';
A
control escape is one of: `%<', `%?', `%|', or `%>'. These are
combined into the conditional execution construct:
%< 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. In other words, `%<' is like
the "if", `%?' is like the "elseif", `%|' is like
"else", and `%>' is like "endif".
A `%<' or `%?' control escape causes its condition to be evaluated. This
condition is a
component or
function. For integer valued
functions or components, the condition is true if the function return or
component value is non-zero, and false if zero. For string valued functions or
components, the condition is true if the function return or component value is
a non-empty string, and false for an empty string.
The `%?' control escape is optional, and may there may be more than one `%?'
control escape in a conditional block. The `%|' control escape is also
optional, but may be included at most once.
Functions expecting an argument generally require an argument 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, functions and components are written
without a leading `%'. Control escape arguments must use a leading `%',
preceded by a space.
For example,
%<(mymbox{from}) To: %{to}%>
writes the value of the header component “From:” to the internal
register named str; then (
mymbox) reads str and writes its result to
the internal register named
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:”.
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 expressions in these forms will print their
value, but outermost escapes which return a boolean value do not result in
printed output.
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 (username)
myhost string the user's local hostname
myname string the user's name
localmbox string the complete local 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
unquote expr string remove RFC-2822 quotes from 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
putnumf expr print num in a fixed width
putlit expr print str without space compression
nodate string integer Argument not a date string (0 or 1)
formataddr expr append arg to str as a
(comma separated) address list
concataddr expr append arg to str as a
(comma separated) address list,
including duplicates,
see Special Handling
putaddr literal print str address list with
arg as optional label;
get line width from num
The (
me) function returns the username of the current user. The (
myhost) function returns the
localname entry in
mts.conf,
or the local hostname if
localname is not configured. The (
myname) function will return the value of the
SIGNATURE
environment variable if set, otherwise will return the passwd GECOS field
(truncated at the first comma if it contains one) for the current user. The (
localmbox) function will return the complete form of the local mailbox,
suitable for use in a “From” header. It will return the
“
Local-Mailbox” profile entry if it is set; if it is not,
it will be equivalent to:
%(myname) <%(me)@%(myhost)>
The following 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 argument. The return value of
functions noted with `*' is computed from 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 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 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 case.)
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.
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) are
somewhat special: they print their result in the minimum number of characters
required, and ignore any leading field width argument. The (
putlit)
function outputs the exact contents of str register without any changes such
as duplicate space removal or control character conversion.
The available output width is kept in an internal register; any output past this
width will be truncated.
A few functions have different behavior depending on what command they are being
invoked from.
In
repl the (
formataddr) function stores all email addresses
encountered into an internal cache and will use this cache to suppress
duplicate addresses. If you need to create an address list that includes
previously-seen addresses you may use the (
concataddr) function, which
is identical to (
formataddr) in all other respects. Note that
(
concataddr) will NOT add addresses to the duplicate-suppression cache.
Sometimes to format function writers it is confusing as to why output is
duplicated. The general rule to remember is simple: If a function or component
escape is used where it starts with a %, then it will generate text in the
output file. Otherwise, it will not.
A good example is a simple attempt to generate a To: header based on the From:
and Reply-To: headers:
%(formataddr %<{reply-to}%|%{from})%(putaddr To: )
Unfortuantely if the Reply-to: header is NOT present, the output line that is
generated will be something like:
What went wrong? When performing the test for the
if clause (%<), the
component is not output because it is considered an argument to the
if
statement (hence the rule about the lack of % applies). But the component
escape in our
else statement (everything after the `%|') is NOT an
argument to anything; the syntax is that it is written with a %, and thus the
value of that component is output. This also has the side effect of setting
the
str register, which is later picked up by the (
formataddr)
function and then output by (
putaddr). This format string has another
bug as well; there should always be a valid width value in the
num
register when (
putaddr) is called, otherwise bad formatting can take
place.
The solution is to use the (
void) function; this will prevent the
function or component from outputting any text. With this in place (and using
(
width) to set the
num register for the width, a better
implementation would look like:
%(formataddr %<{reply-to}%|%(void{from})%(void(width))%(putaddr To: )
It should be noted here that the side-effects of functions and component escapes
still are in force: as a result each component test in the
if-elseif-else-endif clause sets the
str register.
As an additional note, the (
formataddr) and (
concataddr)
functions have some behavior when it comes to the
str register. The
starting point of the register is saved and is used to build up entries in the
address list.
You will find the
ap and
fmtdump utilities invaluable in debugging
problems with format strings.
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; 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,
If a “Date:” field was present, then a space is printed, otherwise
a `*'. Next,
%<(mymbox{from})%<{to}To:%14(decode(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; any MIME-encoded
characters are decoded into the actual characters. Continuing,
%<(zero)%17(decode(friendly{from}))%>
if either of the above two tests failed, then the “From:” address
is printed in a mime-decoded, “user-friendly” format. And
finally,
%(decode{subject})%<{body}<<%{body}>>%>
the mime-decoded subject and initial body (if any) are printed.
For a more complicated example, next consider a possible
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:”.
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.
%<{message-id}In-Reply-To: %{message-id}\n%>\
%<{message-id}References: %<{references} %{references}%>\
%{message-id}\n%>
--------
If a message-id component was present, an “In-Reply-To:” header is
output including the message-id, followed by a “References:”
header with references, if present, and the message-id. 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(message-id)) then
print (“In-reply-to: ”)
print (message-id.value)
print (“\n”)
endif
if (comp_exists(message-id)) then
print (“References: ”)
if (comp_exists(references)) then
print(references.value);
endif
print (message-id.value)
print (“\n”)
endif
One more example: Currently,
nmh supports very large message 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 sensibly 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) conditional is used to test
whether the message number has 5 or more digits. If so, it is printed at full
width: otherwise at 4 digits.
scan(1),
repl(1),
ap(8),
dp(8)
None