-.TH MH-FORMAT %manext5% "January 10, 2015" "%nmhversion%"
-.\"
+.TH MH-FORMAT %manext5% 2015-01-10 "%nmhversion%"
+.
.\" %nmhwarning%
-.\"
+.
.SH NAME
mh-format \- format file for nmh message system
.SH DESCRIPTION
.I format
file during their execution. For example,
.B scan
-uses a format string which directs it how to generate the scan listing
-for each message;
+uses a format string to generate its listing of messages;
.B repl
-uses a format file which directs it
-how to generate the reply to a message, and so on.
+uses a format file to generate message replies, and so on.
.PP
-There are a few alternate scan listing formats available
-in
+There are a number of scan listing formats available,
+including
.IR nmh/etc/scan.time ,
.IR nmh/etc/scan.size ,
and
.IR nmh/etc/scan.timely .
Look in
-.I nmh/etc
+.I %nmhetcdir%
for other
.B scan
and
.B repl
format files which may have been written at your site.
.PP
-It suffices to have your local
+You can have your local
.B nmh
-expert actually write new format
-commands or modify existing ones. This manual section explains how to
-do that. Note: familiarity with the C
+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
.B printf
routine is assumed.
.PP
-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. A literal `%' can be inserted into
-a format file by using the sequence `%%'.
+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 `%%'.
.\" TALK ABOUT SYNTAX FIRST, THEN SEMANTICS
.SS SYNTAX
Format strings are built around
.IR "escape sequences" .
-There are three types of escape sequences: header
+There are three types of escape sequence: header
.IR components ,
built-in
.IR functions ,
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.
-.PP
+.SS "Component escapes"
A
.I component
escape is specified as
.RI `%{ component }',
and
-exists for each header found in the message being processed. For example
+exists for each header in the message being processed. For example,
.RI `%{ date }'
-refers to the \*(lqDate:\*(rq field of the appropriate message.
-All component escapes have a string value. Normally, component values are
+refers to the \*(lqDate:\*(rq 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. 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
-.B ap
+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
+.IR ap (8)
and
-.BR mhl )
+.IR mhl (1) )
use a special component
.RI `%{ text }'
to refer to the text being processed; see their respective man pages for
details and examples.
-.PP
+.SS "Function escapes"
A
.I function
escape is specified as
.RI `%( function )'.
-All functions are built-in, and most have a string or numeric value.
-A function escape may have an
+All functions are built-in, and most have a string or integer value.
+A function escape may take an
.IR argument .
-The argument follows the function escape: separating
-whitespace is discarded:
-.RI `%( function " " argument )'.
+The argument follows the function escape (and any separating
+whitespace is discarded) as in the following example:
+.PP
+.RS 5
+.nf
+.RI %( function " " argument )
+.fi
+.RE
.PP
-In addition to literal numbers or strings,
-the argument to a function escape can be another function, a component,
+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, they are listed without a leading `%'. When control escapes
-are used as function arguments, they written as normally, with
-a leading `%';
+component, the argument is specified without a leading `%'.
+When the argument is a control escape, it is specified
+with a leading `%'.
.SS "Control escapes"
-.PP
A
.I control
-escape is one of: `%<', `%?', `%|', or `%>'.
+escape is one of: `%<', `%?', `%|', or `%>'.
These are combined into the conditional execution construct:
.PP
.RS 5
.nf
.RI "%< " condition " " "format-text"
.RI "%? " condition " " "format-text"
- \&...
+ ...
.RI "%| " "format-text"
%>
.fi
.RE
.PP
-Extra white space is shown here only for clarity. These
-constructs may be nested without ambiguity. They form a general
-.B 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
+(Extra white space is shown here only for clarity.)
+These constructs, which may be nested without ambiguity, form a general
+.B 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".
.PP
-A `%<' or `%?' control escape causes its condition to be evaluated.
+A `%<' or `%?' control escape causes its condition to be evaluated.
This condition is a
.I component
or
.IR 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.
-.PP
-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.
+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.
+.PP
+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.
.SS "Function escapes"
-Functions expecting an argument generally
-require an argument of a particular type.
-In addition to the number and string types,
+Functions expecting an argument generally require an argument of a
+particular type. In addition to the integer and string types,
these include:
.PP
.RS 5
.fi
.RE
.PP
-The types
+The
.I date
and
.I addr
-have the same syntax as
+types have the same syntax as the component type,
.IR comp ,
-but require that the header component be a date string, or address
+but require a header component which is a date, or address,
string, respectively.
.PP
Most arguments not of type
-.IR expr
+.I 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
+When escapes are nested (via expr arguments), evaluation is done
+from innermost to outermost. As noted above, for the
+.I expr
+argument type, functions and components are written without a
leading `%'.
Control escape arguments must use a leading `%', preceded by a space.
.PP
.PP
writes the value of the header component \*(lqFrom:\*(rq to the
internal register named str; then (\fImymbox\fR\^) reads str and
-writes its result to the internal register named
-.IR num ;
-then the control escape evaluates
-.IR num .
+writes its result to the internal register named
+.IR num ;
+then the control escape, `%<', evaluates
+.IR num .
If
-.IR num
-is non-zero, the
-string \*(lqTo:\*(rq is printed followed by the value of the
-header component \*(lqTo:\*(rq.
+.I num
+is non-zero, the string \*(lqTo:\*(rq is printed followed by the
+value of the header component \*(lqTo:\*(rq.
.SS 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
+(as described above) and, in addition, has an integer register
.IR num ,
and a text string register
.IR str .
-When a function escape that
-accepts an optional argument is processed,
+When a function escape that accepts an optional argument is processed,
and the argument is not present, the current value of either
.I num
or
.I str
-is used as the argument: which register is
-used depends on the function, as listed below.
+is substituted as the argument: the register used depends on the function,
+as listed below.
.PP
Component escapes write the value of their message header in
.IR str .
for functions returning integer or boolean values, and in
.I str
for functions returning string values. (The boolean type is a subset
-of integers with usual values 0=false and 1=true.) Control escapes
+of integers, with usual values 0=false and 1=true.) Control escapes
return a boolean value, setting
.I num
to 1 if the last explicit condition
-evaluated by a `%<' or `%?' control
-succeeded, and 0 otherwise.
+evaluated by a `%<' or `%?' control escape succeeded, and 0 otherwise.
.PP
All component escapes, and those function escapes which return an
integer or string value, evaluate to their value as well as setting
.I str
or
.IR num .
-Outermost escape expressions in
-these forms will print
+Outermost escape expressions in these forms will print
their value, but outermost escapes which return a boolean value
do not result in printed output.
.SS Functions
.RS 5
.nf
.ta \w'Fformataddr 'u +\w'Aboolean 'u +\w'Rboolean 'u
-.I "Function Argument Result Description"
+.I "Function Argument Return Description"
msg integer message number
cur integer message is current (0 or 1)
unseen integer message is unseen (0 or 1)
strlen integer length of \fIstr\fR
width integer column width of terminal
charleft integer bytes left in output buffer
-timenow integer seconds since the UNIX epoch
+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
lit literal string Set \fIstr\fR to \fIarg\fR.
lit string Clear \fIstr\fR.
getenv literal string Set \fIstr\fR to environment value of \fIarg\fR
-profile literal string Set \fIstr\fR to profile component \fIarg\fR
+profile literal string Set \fIstr\fR to profile component \fIarg\fR
value
.\" dat literal int return value of dat[arg]
nonzero expr boolean \fInum\fR is non-zero
compval comp integer Set \fInum\fR to \*(lq\fBatoi\fR(\fIcomp\fR\^)\*(rq
.\" compflag comp integer Set \fInum\fR to component flags bits (internal)
.\" decodecomp comp string Set \fIstr\fR to RFC 2047 decoded component text
-decode expr string decode \fIstr\fR as RFC 2047 (MIME-encoded)
+decode expr string decode \fIstr\fR as RFC 2047 (MIME-encoded)
component
unquote expr string remove RFC 2822 quotes from \fIstr\fR
trim expr trim trailing whitespace from \fIstr\fR
putstrf expr print \fIstr\fR in a fixed width
putnum expr print \fInum\fR
putnumf expr print \fInum\fR in a fixed width
-.\" addtoseq literal add msg to sequence (LBL option)
putlit expr print \fIstr\fR without space compression
zputlit expr print \fIstr\fR without space compression;
\fIstr\fR must occupy no width on display
.fi
.RE
.PP
-The (\fIme\fR\^) function returns the username of the current user. The
-(\fImyhost\fR\^) function returns the
+The (\fIme\fR\^) function returns the username of the current user.
+The (\fImyhost\fR\^) function returns the
.B localname
entry in
.IR mts.conf ,
is not configured. The (\fImyname\fR\^) function will return the value of
the
.B SIGNATURE
-environment variable if set, otherwise will return the passwd GECOS field
+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 (\fIlocalmbox\fR\^) function will return the complete
form of the local mailbox, suitable for use in a \*(lqFrom\*(rq header.
It will return the
.RI \*(lq Local-Mailbox \*(rq
-profile entry if it is set; if it is not, it will be equivalent to:
+profile entry if there is one; if not, it will be equivalent to:
.PP
.RS 5
.nf
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
+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
.fi
.RE
.PP
-These functions require an address component as an argument.
+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.
.PP
This function checks each of the addresses in the header component
\*(lq\fIcomp\fR\*(rq against the user's mailbox name and any
.RI \*(lq Alternate-Mailboxes \*(rq.
-It returns true if any address matches,
-however, it also returns true if the \*(lq\fIcomp\fR\*(rq header is not
-present in the message. If needed, the (\fInull\fR\^) function can be
-used to explicitly test for this case.)
+It returns true if any address matches. However, it also returns true
+if the \*(lq\fIcomp\fR\*(rq header is not present in the message.
+If needed, the (\fInull\fR\^) function can be used to explicitly
+test for this case.)
.SS Formatting
When a function or component escape is interpreted and the result will
-be immediately printed, an optional field width can be specified to
+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(\fIsize\fR\^) will print at most 4 digits of the
message size; overflow will be indicated by a `?' in the first position
right-justification of the string within the field, with padding on
the left up to the field width.
The functions (\fIputnum\fR\^) and
-(\fIputstr\fR\^) are somewhat special: they print their result in the minimum number of characters
-required, and ignore any leading field width argument. The (\fIputlit\fR\^)
-function outputs the exact contents of the str register without any changes
-such as duplicate space removal or control character conversion.
-The (\fIzputlit\fR\^) function similarly 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.
+(\fIputstr\fR\^) are somewhat special: they print their result in the
+minimum number of characters required, and ignore any leading field width
+argument. The (\fIputlit\fR\^) function outputs the exact contents of the
+str register without any changes such as duplicate space removal or control
+character conversion. Similarly, the (\fIzputlit\fR\^) 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.
.PP
There are a limited number of function escapes to output terminal escape
sequences. These sequences are retrieved from the
database according to the current terminal setting. The (\fIbold\fR\^),
(\fIunderline\fR\^), and (\fIstandout\fR\^) escapes set bold mode,
underline mode, and standout mode respectively.
-.PP
(\fIhascolor\fR\^)
can be used to determine if the current terminal supports color.
(\fIfgcolor\fR\^) and (\fIbgcolor\fR\^) 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. (\fIresetterm\fR\^) resets all terminal
-attributes back to their default setting.
-.PP
-All of these terminal escape should be used in conjunction with
-(\fIzputlit\fR\^) (preferred) or (\fIputlit\fR\^), as the normal
-(\fIputstr\fR\^) function will strip out control characters.
+attributes to their default setting. These terminal escapes should be
+used in conjunction with (\fIzputlit\fR\^) (preferred) or
+(\fIputlit\fR\^), as the normal (\fIputstr\fR\^) function will strip
+out control characters.
.PP
The available output width is kept in an internal register; any output
-past this width will be truncated. The one exception to this is
-(\fIzputlit\fR\^) functions will still be executed in case a terminal reset
-code is being placed at the end of the line.
+exceeding this width will be truncated. The one exception to this is that
+(\fIzputlit\fR\^) functions will still be executed if a terminal
+reset code is being placed at the end of a line.
.SS Special Handling
-A few functions have different behavior depending on what command they are
-being invoked from.
+Some functions have different behavior depending on the command they are
+invoked from.
.PP
In
-.BR repl
+.B repl
the (\fIformataddr\fR\^) 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 (\fIconcataddr\fR\^) function, which is identical
to (\fIformataddr\fR\^) in all other respects. Note that (\fIconcataddr\fR\^)
-will NOT add addresses to the duplicate-suppression cache.
+does
+.I not
+add addresses to the duplicate-suppression cache.
.SS Other Hints and Tips
-Sometimes to format function writers it is confusing as to why output is
+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 is used where it starts with a %, then it will generate
-text in the output file. Otherwise, it will not.
+component escape begins with a `%', it will generate text in the output file.
+Otherwise, it will not.
.PP
A good example is a simple attempt to generate a To: header based on
the From: and Reply-To: headers:
.fi
.RE
.PP
-Unfortuantely if the Reply-to: header is NOT present, the output line that is
-generated will be something like:
+Unfortunately, if the Reply-to: header is
+.I not
+present, the output line
+will be something like:
.PP
.RS 5
.nf
clause (%<), the component is not output because it is considered an
argument to the
.B if
-statement (hence the rule about the lack of % applies). But the component
+statement (so the rule about not starting with % applies). But the component
escape in our
.B 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
+statement (everything after the `%|') is
+.I 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
.I str
register, which is later picked up by the (\fIformataddr\fR\^) function
-and then output by (\fIputaddr\fR\^). This format string has another bug
-as well; there should always be a valid width value in the
+and then output by (\fIputaddr\fR\^). The example format string above
+has another bug: there should always be a valid width value in the
.I num
register when (\fIputaddr\fR\^) is called, otherwise bad formatting can take
place.
function or component from outputting any text. With this in place (and
using (\fIwidth\fR\^) to set the
.I num
-register for the width, a better implementation would look like:
+register for the width) a better implementation would look like:
.PP
.RS 3
.nf
.fi
.RE
.PP
-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
-.B if\-elseif\-else\-endif
+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
+.B if-elseif-else-endif
clause sets the
.I str
register.
build up entries in the address list.
.PP
You will find the
-.B fmttest
+.IR fmttest (1)
utility invaluable when debugging problems with format strings.
.SS Examples
-With all this in mind,
-here's the default format string for
+With all the above in mind, here is a breakdown of the default format string for
.BR scan .
-It's been divided into several pieces for readability.
The first part is:
.PP
.RS
.RE
.PP
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 \*(lqReplied:\*(rq field is present then a `\-'
-else if an \*(lqEncrypted:\*(rq field is present then an `E' otherwise
-a space should be printed. Next:
+If the message is the current message then a `+', else a space, should
+be printed; if a \*(lqReplied:\*(rq field is present then a `\-',
+else if an \*(lqEncrypted:\*(rq field is present then an `E', otherwise
+a space, should be printed. Next:
.PP
.RS
.nf
.fi
.RE
.PP
-If a \*(lqDate:\*(rq field was present,
-then a space is printed, otherwise a `*'.
+If a \*(lqDate:\*(rq field is present it is printed, followed by a space;
+otherwise a `*' is printed.
Next,
.PP
.RS 5
.PP
the mime-decoded subject and initial body (if any) are printed.
.PP
-For a more complicated example, next consider
-a possible
+For a more complicated example, consider a possible
.I replcomps
format file.
.PP
.PP
This clears
.I str
-and formats the \*(lqReply-To:\*(rq header
+and formats the \*(lqReply-To:\*(rq header
if present. If not present, the else-if clause is executed.
.PP
.RS 5
.fi
.RE
.PP
-This formats the
+This formats the
\*(lqFrom:\*(rq, \*(lqSender:\*(rq and \*(lqReturn-Path:\*(rq
headers, stopping as soon as one of them is present. Next:
.PP
.PP
If the \fIformataddr\fR result is non-null, it is printed as
an address (with line folding if needed) in a field \fIwidth\fR
-wide with a leading label of \*(lqTo:\*(rq.
+wide, with a leading label of \*(lqTo:\*(rq.
.PP
.RS 5
.nf
.\".PP
One more example: Currently,
.B nmh
-supports very
-large message numbers, and it is not uncommon for a folder
+supports very large message numbers, and it is not uncommon for a folder
to have far more than 10000 messages.
.\" (Indeed, the original MH
.\" tutorial document by Rose and Romine is entitled "How to
.\" process 200 messages a day and still get some real work
.\" done." The authors apparently only planned to get
.\" real work done for about 50 days per folder.)
-Nonetheless (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.
+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:
.PP
The current message number is placed in \fInum\fP.
(Note that
.RI ( msg )
-is an int function, not a component.)
+is a function escape which returns an integer, it is not a component.)
The
.RI ( gt )
conditional
projects / nmh / blobdiff