Provided by: nmh_1.7.1~RC3-1build1_amd64 
NAME
mh-format - formatting language for nmh message system
DESCRIPTION
Several nmh commands utilize either a format string or a format file during their
execution. For example, scan uses a format string to generate its listing of messages;
repl uses a format file to generate message replies, and so on.
There are a number of scan listing formats available, including nmh/etc/scan.time,
nmh/etc/scan.size, and nmh/etc/scan.timely. Look in /etc/nmh for other scan and repl
format files which may have been written at your site.
You can have your local nmh expert write new format commands or modify existing ones, or
you can try your hand at it yourself. This manual section explains how to do that. Note:
some familiarity with the C printf routine is assumed.
A format string consists of ordinary text combined with 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. A literal `%' can be inserted into
a format file by using the sequence `%%'.
SYNTAX
Format strings are built around escape sequences. There are three types of escape
sequence: 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.
Component escapes
A component escape is specified as `%{component}', and exists for each header in the
message being processed. For example, `%{date}' refers to the “Date:” field of the
message. All component escapes have a string value. Such values are usually compressed
by converting any control characters (tab and newline included) to spaces, then eliding
any leading or multiple spaces. Some commands, however, may interpret some component
escapes differently; be sure to refer to each command's manual entry for details. Some
commands (such as ap(8) and mhl(1)) use a special component `%{text}' to refer to the text
being processed; see their respective man pages for details and examples.
Function escapes
A function escape is specified as `%(function)'. All functions are built-in, and most
have a string or integer value. A function escape may take an argument. The argument
follows the function escape (and any separating whitespace is discarded) as in the
following example:
%(function argument)
In addition to literal numbers or strings, the argument to a function escape can be
another function, or a component, or a control escape. When the argument is a function or
a component, the argument is specified without a leading `%'. When the argument is a
control escape, it is specified with a leading `%'.
Control escapes
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, which may be nested
without ambiguity, 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 components and functions whose value is an integer, the
condition is true if it is non-zero, and false if zero. For components and functions
whose value is a string, the condition is true it is a non-empty string, and false if an
empty string.
The `%?' control escape is optional, and can be used multiple times in a conditional
block. The `%|' control escape is also optional, but may only be used once.
Function escapes
Functions expecting an argument generally require an argument of a particular type. In
addition to the integer 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 date and addr types have the same syntax as the component type, comp, but require a
header component which is a date, or address, string, respectively.
Most arguments not of type expr are required. When escapes are nested (via expr
arguments), evaluation is done from innermost to outermost. 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:”.
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 substituted as the argument: the register 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 escape 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.
Functions
The function escapes may be roughly grouped into a few categories.
Function Argument Return 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 column width of terminal
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
multiply literal integer num multiplied by arg
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 whitespace from str
kilo expr string express in SI units: 15.9K, 2.3M, etc.
%(kilo) scales by factors of 1000,
kibi expr string express in IEC units: 15.5Ki, 2.2Mi.
%(kibi) scales by factors of 1024.
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
zputlit expr print str without space compression;
str must occupy no width on display
bold string set terminal bold mode
underline string set terminal underlined mode
standout string set terminal standout mode
resetterm string reset all terminal attributes
hascolor boolean terminal supports color
fgcolor literal string set terminal foreground color
bgcolor literal string set terminal background color
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 it 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 there is one; if 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 minutes
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 RFC 822 rendering
pretty date string user-friendly rendering
nodate date integer returns 1 if date is invalid
The following 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 RFC 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)
getmymbox addr string the user's (first) address,
with personal name
getmyaddr addr string the user's (first) address,
without personal name
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.)
Formatting
When a function or component escape is interpreted and the result will be printed
immediately, 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. Using a negative value for the field
width causes right-justification within the field, with padding on the left up to the
field width. Padding is with spaces except for a left-padded putnumf when the width
starts with zero. 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 the str register
without any changes such as duplicate space removal or control character conversion.
Similarly, the (zputlit) function outputs the exact contents of the str register, but
requires that those contents not occupy any output width. It can therefore be used for
outputting terminal escape sequences.
There are a limited number of function escapes to output terminal escape sequences. These
sequences are retrieved from the terminfo(5) database according to the current terminal
setting. The (bold), (underline), and (standout) escapes set bold mode, underline mode,
and standout mode respectively. (hascolor) can be used to determine if the current
terminal supports color. (fgcolor) and (bgcolor) set the foreground and background colors
respectively. Both of these escapes take one literal argument, the color name, which can
be one of: black, red, green, yellow, blue, magenta, cyan, white. (resetterm) resets all
terminal attributes to their default setting. These terminal escapes should be used in
conjunction with (zputlit) (preferred) or (putlit), as the normal (putstr) function will
strip out control characters.
The available output width is kept in an internal register; any output exceeding this
width will be truncated. The one exception to this is that (zputlit) functions will still
be executed if a terminal reset code is being placed at the end of a line.
Special Handling
Some functions have different behavior depending on the command they are 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) does not add addresses to the duplicate-suppression cache.
Other Hints and Tips
Sometimes, the writer of a format function is confused because output is duplicated. The
general rule to remember is simple: If a function or component escape begins with a `%',
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: )
Unfortunately, if the Reply-to: header is not present, the output line will be something
like:
My From User <from@example.com>To: My From User <from@example.com>
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 (so the rule about not
starting with % applies). But the component escape in our else statement (everything
after the `%|') is not an argument to anything; it begins 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). The
example format string above has another bug: 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 function and component escapes are still
in force and, 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 special 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 fmttest(1) utility invaluable when debugging problems with format
strings.
Examples
With all the above in mind, here is a breakdown of the default format string for scan.
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 is present it is printed, followed by a space; otherwise a `*' is
printed. 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, 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:”.
%<{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 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. Nonetheless (as noted above)
the various scan format strings, inherited from older MH versions, are generally hard-
coded to 4 digits for the message number. Thereafter, formatting problems 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 a function escape which
returns an integer, it is 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.
SEE ALSO
scan(1), repl(1), fmttest(1),
CONTEXT
None