+.TH MH-FORMAT %manext5% "November 4, 2012" "%nmhversion%"
.\"
.\" %nmhwarning%
.\"
-.TH MH-FORMAT %manext5% "%nmhdate%" MH.6.8 [%nmhversion%]
.SH NAME
mh-format \- format file for nmh message system
.SH DESCRIPTION
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.
-
.\" TALK ABOUT SYNTAX FIRST, THEN SEMANTICS
.SS SYNTAX
Format strings are built around
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.
+to refer to each command's manual entry for complete details. Some commands
+(such as
+.B ap
+and
+.BR mhl )
+use a special component
+.RI `%{ text }'
+to refer to the text being processed; see their respective man pages for
+details and examples.
.PP
A
.I function
component, they are listed without a leading `%'. When control escapes
are used as function arguments, they written as normally, with
a leading `%';
-
.SS "Control escapes"
.PP
A
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 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.
-
.SS "Function escapes"
Functions expecting an argument generally
require an argument of a particular type.
.RS 5
.nf
.ta +\w'Argument 'u +\w'An optional component, 'u
-.I Argument Description Example Syntax
+.I "Argument Description Example Syntax"
literal A literal number %(\fIfunc\fR 1234)
or string %(\fIfunc\fR text string)
comp Any component %(\fIfunc\fR\^{\fIin-reply-to\fR\^})
.RS 5
.nf
.ta \w'Fformataddr 'u +\w'Aboolean 'u +\w'Rboolean 'u
-.I Function Argument Result Description
+.I "Function Argument Result Description"
msg integer message number
cur integer message is current (0 or 1)
unseen integer message is unseen (0 or 1)
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
+myhost string the user's local hostname
+myname string the user's name
+localmbox string the complete local mailbox
eq literal boolean \fInum\fR == \fIarg\fR
ne literal boolean \fInum\fR != \fIarg\fR
gt literal boolean \fInum\fR > \fIarg\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
-nodate string integer Argument not a date string (0 or 1)
+zputlit expr print \fIstr\fR without space compression;
+ \fIstr\fR must occupy no width on display
formataddr expr append \fIarg\fR to \fIstr\fR as a
(comma separated) address list
concataddr expr append \fIarg\fR to \fIstr\fR as a
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 for
-the current user.
+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 (\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:
+.PP
+.RS 5
+.nf
+%(myname) <%(me)@%(myhost)>
+.fi
+.RE
.PP
The following functions require a date component as an argument:
.PP
.RS 5
.nf
.ta \w'Fformataddr 'u +\w'Aboolean 'u +\w'Rboolean 'u
-.I Function Argument Return Description
+.I "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)
.RS 5
.nf
.ta \w'Fformataddr 'u +\w'Aboolean 'u +\w'Rboolean 'u
-.I Function Argument Return Description
+.I "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*
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 str register without any changes
+function outputs the exact contents of the str register without any changes
such as duplicate space removal or control character conversion.
+The (\fIzputlit\fR\^) 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.
.PP
The available output width is kept in an internal register; any output
past this width will be truncated.
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.
+.SS Other Hints and Tips
+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.
+.PP
+A good example is a simple attempt to generate a To: header based on
+the From: and Reply-To: headers:
+.PP
+.RS 5
+.nf
+%(formataddr %<{reply-to}%|%{from})%(putaddr To: )
+.fi
+.RE
+.PP
+Unfortuantely if the Reply-to: header is NOT present, the output line that is
+generated will be something like:
+.PP
+.RS 5
+.nf
+My From User <from@example.com>To: My From User <from@example.com>
+.fi
+.RE
+.PP
+What went wrong? When performing the test for the
+.B if
+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
+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
+.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
+.I num
+register when (\fIputaddr\fR\^) is called, otherwise bad formatting can take
+place.
+.PP
+The solution is to use the (\fIvoid\fR\^) function; this will prevent the
+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:
+.PP
+.RS 3
+.nf
+%(formataddr %<{reply-to}%|%(void{from})%(void(width))%(putaddr To: )
+.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
+clause sets the
+.I str
+register.
+.PP
+As an additional note, the (\fIformataddr\fR\^) and (\fIconcataddr\fR\^)
+functions have some behavior when it comes to the
+.I str
+register. The starting point of the register is saved and is used to
+build up entries in the address list.
+.PP
+You will find the
+.B ap
+and
+.B fmtdump
+utilities invaluable in debugging problems with format strings.
.SS Examples
With all this in mind,
here's the default format string for
switch was given to
.B repl
(see
-.BR repl (1)
+.IR repl (1)
for more details about %{\fIfcc\fR\^}),
an \*(lqFcc:\*(rq header is output.
.PP
is used to test whether the message number
has 5
or more digits.
-If so, it is printed at full width: otherwise
+If so, it is printed at full width, otherwise
at 4 digits.
.SH "SEE ALSO"
-scan(1), repl(1), ap(8), dp(8)
-
+.IR scan (1),
+.IR repl (1),
+.IR ap (8),
+.IR dp (8)
.SH CONTEXT
None
projects / mmh / blobdiff