Provided by: mmh_0.3-3_amd64 
NAME
mh-format - format file for mh message system
DESCRIPTION
Several mmh 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, e.g. scan.nmh, scan.mailx, and scan.timely.
Look in /etc/mmh for other scan and repl format files.
This manual section explains how to write and modify format commands. 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.
SYNTAX
Format strings are built around escape sequences. There are four types of escape sequences:
1) header components %{component}
2) built-in functions %(function arg)
3) flow control %< ... %? ... %| ... %>
4) comments %; ...
Comments may be inserted in most places where no function argument is 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.
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 `%'.
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 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 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.
Function escapes
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:'.
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 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 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 and print it
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
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
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 RFC-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 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)
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 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 available output width is kept in an internal register; any output past this width will be truncated.
Examples
With all this in mind, here's a format string for scan. It's been divided into several pieces for
readability. The first part is:
%4(msg)%<(cur)+%| %>%<{replied}-%| %>
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 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(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})
the mime-decoded subject is 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:' or `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:'.
%<{subject}Subject: Re: %(decode{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: Mmh supports very large message numbers, and it is not uncommon for a folder to have
far more than 10000 messages. Nonetheless several 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 mh 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.
SEE ALSO
scan(1), repl(1), ap(8), dp(8)
CONTEXT
None