Manpages

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

unmailto

expr

string

remove ’mailto:’ and < > from str

trim

expr

trim 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

COMMENTS