perlform.1

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

.IX Xref "format, fill mode"
.IX Subsection "Using Fill Mode"
On text fields the caret enables a kind of fill mode.  Instead of an
arbitrary expression, the value supplied must be a scalar variable
that contains a text string.  Perl puts the next portion of the text into
the field, and then chops off the front of the string so that the next time
the variable is referenced, more of the text can be printed.  (Yes, this
means that the variable itself is altered during execution of the \fIwrite()\fR
call, and is not restored.)  The next portion of text is determined by
a crude line breaking algorithm. You may use the carriage return character
(\f(CW\*(C`\er\*(C'\fR) to force a line break. You can change which characters are legal 
to break on by changing the variable \f(CW$:\fR (that's 
\&\f(CW$FORMAT_LINE_BREAK_CHARACTERS\fR if you're using the English module) to a 
list of the desired characters.
.PP
Normally you would use a sequence of fields in a vertical stack associated 
with the same scalar variable to print out a block of text. You might wish 
to end the final field with the text \*(L"...\*(R", which will appear in the output 
if the text was too long to appear in its entirety.
.Sh "Suppressing Lines Where All Fields Are Void"
.IX Xref "format, suppressing lines"
.IX Subsection "Suppressing Lines Where All Fields Are Void"
Using caret fields can produce lines where all fields are blank. You can
suppress such lines by putting a \*(L"~\*(R" (tilde) character anywhere in the
line.  The tilde will be translated to a space upon output.
.Sh "Repeating Format Lines"
.IX Xref "format, repeating lines"
.IX Subsection "Repeating Format Lines"
If you put two contiguous tilde characters \*(L"~~\*(R" anywhere into a line,
the line will be repeated until all the fields on the line are exhausted,
i.e. undefined. For special (caret) text fields this will occur sooner or
later, but if you use a text field of the at variety, the  expression you
supply had better not give the same value every time forever! (\f(CW\*(C`shift(@f)\*(C'\fR
is a simple example that would work.)  Don't use a regular (at) numeric 
field in such lines, because it will never go blank.
.Sh "Top of Form Processing"
.IX Xref "format, top of form top header"
.IX Subsection "Top of Form Processing"
Top-of-form processing is by default handled by a format with the
same name as the current filehandle with \*(L"_TOP\*(R" concatenated to it.
It's triggered at the top of each page.  See \*(L"write\*(R" in perlfunc.
.PP
Examples:
.PP
.Vb 10
\& # a report on the /etc/passwd file
\& format STDOUT_TOP =
\&                         Passwd File
\& Name                Login    Office   Uid   Gid Home
\& \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-
\& .
\& format STDOUT =
\& @<<<<<<<<<<<<<<<<<< @||||||| @<<<<<<@>>>> @>>>> @<<<<<<<<<<<<<<<<<
\& $name,              $login,  $office,$uid,$gid, $home
\& .
\&
\&
\& # a report from a bug report form
\& format STDOUT_TOP =
\&                         Bug Reports
\& @<<<<<<<<<<<<<<<<<<<<<<<     @|||         @>>>>>>>>>>>>>>>>>>>>>>>
\& $system,                      $%,         $date
\& \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-
\& .
\& format STDOUT =
\& Subject: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
\&          $subject
\& Index: @<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
\&        $index,                       $description
\& Priority: @<<<<<<<<<< Date: @<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
\&           $priority,        $date,   $description
\& From: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
\&       $from,                         $description
\& Assigned to: @<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
\&              $programmer,            $description
\& ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
\&                                      $description
\& ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
\&                                      $description
\& ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
\&                                      $description
\& ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
\&                                      $description
\& ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<...
\&                                      $description
\& .
.Ve
.PP
It is possible to intermix \fIprint()\fRs with \fIwrite()\fRs on the same output
channel, but you'll have to handle \f(CW\*(C`$\-\*(C'\fR (\f(CW$FORMAT_LINES_LEFT\fR)
yourself.
.Sh "Format Variables"
.IX Xref "format variables format, variables"
.IX Subsection "Format Variables"
The current format name is stored in the variable \f(CW$~\fR (\f(CW$FORMAT_NAME\fR),
and the current top of form format name is in \f(CW$^\fR (\f(CW$FORMAT_TOP_NAME\fR).
The current output page number is stored in \f(CW$%\fR (\f(CW$FORMAT_PAGE_NUMBER\fR),
and the number of lines on the page is in \f(CW$=\fR (\f(CW$FORMAT_LINES_PER_PAGE\fR).
Whether to autoflush output on this handle is stored in \f(CW$|\fR
(\f(CW$OUTPUT_AUTOFLUSH\fR).  The string output before each top of page (except
the first) is stored in \f(CW$^L\fR (\f(CW$FORMAT_FORMFEED\fR).  These variables are
set on a per-filehandle basis, so you'll need to \fIselect()\fR into a different
one to affect them:
.PP
.Vb 4
\&    select((select(OUTF),
\&            $~ = "My_Other_Format",
\&            $^ = "My_Top_Format"
\&           )[0]);
.Ve
.PP
Pretty ugly, eh?  It's a common idiom though, so don't be too surprised
when you see it.  You can at least use a temporary variable to hold
the previous filehandle: (this is a much better approach in general,
because not only does legibility improve, you now have intermediary
stage in the expression to single-step the debugger through):
.PP
.Vb 4
\&    $ofh = select(OUTF);
\&    $~ = "My_Other_Format";
\&    $^ = "My_Top_Format";
\&    select($ofh);
.Ve
.PP
If you use the English module, you can even read the variable names:
.PP
.Vb 5
\&    use English \*(Aq\-no_match_vars\*(Aq;
\&    $ofh = select(OUTF);
\&    $FORMAT_NAME     = "My_Other_Format";
\&    $FORMAT_TOP_NAME = "My_Top_Format";
\&    select($ofh);
.Ve
.PP
But you still have those funny \fIselect()\fRs.  So just use the FileHandle
module.  Now, you can access these special variables using lowercase
method names instead:
.PP
.Vb 3
\&    use FileHandle;
\&    format_name     OUTF "My_Other_Format";
\&    format_top_name OUTF "My_Top_Format";
.Ve
.PP
Much better!
.SH "NOTES"
.IX Header "NOTES"
Because the values line may contain arbitrary expressions (for at fields,
not caret fields), you can farm out more sophisticated processing
to other functions, like \fIsprintf()\fR or one of your own.  For example:
.PP
.Vb 4
\&    format Ident =
\&        @<<<<<<<<<<<<<<<
\&        &commify($n)
\&    .
.Ve
.PP
To get a real at or caret into the field, do this:
.PP
.Vb 4
\&    format Ident =
\&    I have an @ here.
\&            "@"
\&    .
.Ve
.PP
To center a whole line of text, do something like this:
.PP
.Vb 4
\&    format Ident =
\&    @|||||||||||||||||||||||||||||||||||||||||||||||
\&            "Some text line"
\&    .
.Ve
.PP
There is no builtin way to say \*(L"float this to the right hand side
of the page, however wide it is.\*(R"  You have to specify where it goes.
The truly desperate can generate their own format on the fly, based
on the current number of columns, and then \fIeval()\fR it:
.PP
.Vb 9
\&    $format  = "format STDOUT = \en"
\&             . \*(Aq^\*(Aq . \*(Aq<\*(Aq x $cols . "\en"
\&             . \*(Aq$entry\*(Aq . "\en"
\&             . "\et^" . "<" x ($cols\-8) . "~~\en"
\&             . \*(Aq$entry\*(Aq . "\en"
\&             . ".\en";
\&    print $format if $Debugging;
\&    eval $format;
\&    die $@ if $@;
.Ve
.PP
Which would generate a format looking something like this:
.PP
.Vb 6
\& format STDOUT =
\& ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
\& $entry
\&         ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<~~
\& $entry
\& .
.Ve
.PP
Here's a little program that's somewhat like \fIfmt\fR\|(1):
.PP
.Vb 3
\& format =
\& ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< ~~
\& $_
\&
\& .
\&
\& $/ = \*(Aq\*(Aq;
\& while (<>) {
\&     s/\es*\en\es*/ /g;
\&     write;
\& }
.Ve
.Sh "Footers"
.IX Xref "format, footer footer"
.IX Subsection "Footers"
While \f(CW$FORMAT_TOP_NAME\fR contains the name of the current header format,
there is no corresponding mechanism to automatically do the same thing
for a footer.  Not knowing how big a format is going to be until you
evaluate it is one of the major problems.  It's on the \s-1TODO\s0 list.
.PP
Here's one strategy:  If you have a fixed-size footer, you can get footers
by checking \f(CW$FORMAT_LINES_LEFT\fR before each \fIwrite()\fR and print the footer
yourself if necessary.
.PP
Here's another strategy: Open a pipe to yourself, using \f(CW\*(C`open(MYSELF, "|\-")\*(C'\fR
(see \*(L"\fIopen()\fR\*(R" in perlfunc) and always \fIwrite()\fR to \s-1MYSELF\s0 instead of \s-1STDOUT\s0.
Have your child process massage its \s-1STDIN\s0 to rearrange headers and footers
however you like.  Not very convenient, but doable.
.Sh "Accessing Formatting Internals"
.IX Xref "format, internals"
.IX Subsection "Accessing Formatting Internals"
For low-level access to the formatting mechanism.  you may use \fIformline()\fR
and access \f(CW$^A\fR (the \f(CW$ACCUMULATOR\fR variable) directly.
.PP
For example:
.PP
.Vb 3
\&    $str = formline <<\*(AqEND\*(Aq, 1,2,3;
\&    @<<<  @|||  @>>>
\&    END
\&
\&    print "Wow, I just stored \`$^A\*(Aq in the accumulator!\en";
.Ve
.PP
Or to make an \fIswrite()\fR subroutine, which is to \fIwrite()\fR what \fIsprintf()\fR
is to \fIprintf()\fR, do this:
.PP
.Vb 8
\&    use Carp;
\&    sub swrite {
\&        croak "usage: swrite PICTURE ARGS" unless @_;
\&        my $format = shift;
\&        $^A = "";
\&        formline($format,@_);
\&        return $^A;
\&    }
\&
\&    $string = swrite(<<\*(AqEND\*(Aq, 1, 2, 3);
\& Check me out
\& @<<<  @|||  @>>>
\& END
\&    print $string;
.Ve
.SH "WARNINGS"
.IX Header "WARNINGS"
The lone dot that ends a format can also prematurely end a mail
message passing through a misconfigured Internet mailer (and based on
experience, such misconfiguration is the rule, not the exception).  So
when sending format code through mail, you should indent it so that
the format-ending dot is not on the left margin; this will prevent
\&\s-1SMTP\s0 cutoff.
.PP
Lexical variables (declared with \*(L"my\*(R") are not visible within a
format unless the format is declared within the scope of the lexical
variable.  (They weren't visible at all before version 5.001.)
.PP
Formats are the only part of Perl that unconditionally use information
from a program's locale; if a program's environment specifies an
\&\s-1LC_NUMERIC\s0 locale, it is always used to specify the decimal point
character in formatted output.  Perl ignores all other aspects of locale
handling unless the \f(CW\*(C`use locale\*(C'\fR pragma is in effect.  Formatted output
cannot be controlled by \f(CW\*(C`use locale\*(C'\fR because the pragma is tied to the
block structure of the program, and, for historical reasons, formats
exist outside that block structure.  See perllocale for further
discussion of locale handling.
.PP
Within strings that are to be displayed in a fixed length text field,
each control character is substituted by a space. (But remember the
special meaning of \f(CW\*(C`\er\*(C'\fR when using fill mode.) This is done to avoid
misalignment when control characters \*(L"disappear\*(R" on some output media.