perlfaq9.1

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.

.PP
.Vb 3
\&    <!\-\- This section commented out.
\&        <B>You can\*(Aqt see me!</B>
\&    \-\->
.Ve
.Sh "How do I extract URLs?"
.IX Subsection "How do I extract URLs?"
You can easily extract all sorts of URLs from \s-1HTML\s0 with
\&\f(CW\*(C`HTML::SimpleLinkExtor\*(C'\fR which handles anchors, images, objects,
frames, and many other tags that can contain a \s-1URL\s0.  If you need
anything more complex, you can create your own subclass of
\&\f(CW\*(C`HTML::LinkExtor\*(C'\fR or \f(CW\*(C`HTML::Parser\*(C'\fR.  You might even use
\&\f(CW\*(C`HTML::SimpleLinkExtor\*(C'\fR as an example for something specifically
suited to your needs.
.PP
You can use URI::Find to extract URLs from an arbitrary text document.
.PP
Less complete solutions involving regular expressions can save
you a lot of processing time if you know that the input is simple.  One
solution from Tom Christiansen runs 100 times faster than most
module based approaches but only extracts URLs from anchors where the first
attribute is \s-1HREF\s0 and there are no other attributes.
.PP
.Vb 7
\&        #!/usr/bin/perl \-n00
\&        # qxurl \- [e-mail]
\&        print "$2\en" while m{
\&            < \es*
\&              A \es+ HREF \es* = \es* (["\*(Aq]) (.*?) \e1
\&            \es* >
\&        }gsix;
.Ve
.Sh "How do I download a file from the user's machine?  How do I open a file on another machine?"
.IX Subsection "How do I download a file from the user's machine?  How do I open a file on another machine?"
In this case, download means to use the file upload feature of \s-1HTML\s0
forms.  You allow the web surfer to specify a file to send to your web
server.  To you it looks like a download, and to the user it looks
like an upload.  No matter what you call it, you do it with what's
known as \fBmultipart/form\-data\fR encoding.  The \s-1CGI\s0.pm module (which
comes with Perl as part of the Standard Library) supports this in the
\&\fIstart_multipart_form()\fR method, which isn't the same as the \fIstartform()\fR
method.
.PP
See the section in the \s-1CGI\s0.pm documentation on file uploads for code
examples and details.
.Sh "How do I make an \s-1HTML\s0 pop-up menu with Perl?"
.IX Subsection "How do I make an HTML pop-up menu with Perl?"
(contributed by brian d foy)
.PP
The \s-1CGI\s0.pm module (which comes with Perl) has functions to create
the \s-1HTML\s0 form widgets. See the \s-1CGI\s0.pm documentation for more
examples.
.PP
.Vb 3
\&        use CGI qw/:standard/;
\&        print header,
\&                start_html(\*(AqFavorite Animals\*(Aq),
\&
\&                start_form,
\&                        "What\*(Aqs your favorite animal? ",
\&        popup_menu(
\&                \-name   => \*(Aqanimal\*(Aq,
\&                        \-values => [ qw( Llama Alpaca Camel Ram ) ]
\&                        ),
\&        submit,
\&
\&                end_form,
\&        end_html;
.Ve
.Sh "How do I fetch an \s-1HTML\s0 file?"
.IX Subsection "How do I fetch an HTML file?"
One approach, if you have the lynx text-based \s-1HTML\s0 browser installed
on your system, is this:
.PP
.Vb 2
\&    $html_code = \`lynx \-source $url\`;
\&    $text_data = \`lynx \-dump $url\`;
.Ve
.PP
The libwww-perl (\s-1LWP\s0) modules from \s-1CPAN\s0 provide a more powerful way
to do this.  They don't require lynx, but like lynx, can still work
through proxies:
.PP
.Vb 3
\&    # simplest version
\&    use LWP::Simple;
\&    $content = get($URL);
\&
\&    # or print HTML from a URL
\&    use LWP::Simple;
\&    getprint "http://www.linpro.no/lwp/";
\&
\&    # or print ASCII from HTML from a URL
\&    # also need HTML\-Tree package from CPAN
\&    use LWP::Simple;
\&    use HTML::Parser;
\&    use HTML::FormatText;
\&    my ($html, $ascii);
\&    $html = get("http://www.perl.com/");
\&    defined $html
\&        or die "Can\*(Aqt fetch HTML from http://www.perl.com/";
\&    $ascii = HTML::FormatText\->new\->format(parse_html($html));
\&    print $ascii;
.Ve
.Sh "How do I automate an \s-1HTML\s0 form submission?"
.IX Subsection "How do I automate an HTML form submission?"
If you are doing something complex, such as moving through many pages
and forms or a web site, you can use \f(CW\*(C`WWW::Mechanize\*(C'\fR.  See its
documentation for all the details.
.PP
If you're submitting values using the \s-1GET\s0 method, create a \s-1URL\s0 and encode
the form using the \f(CW\*(C`query_form\*(C'\fR method:
.PP
.Vb 2
\&    use LWP::Simple;
\&    use URI::URL;
\&
\&    my $url = url(\*(Aqhttp://www.perl.com/cgi\-bin/cpan_mod\*(Aq);
\&    $url\->query_form(module => \*(AqDB_File\*(Aq, readme => 1);
\&    $content = get($url);
.Ve
.PP
If you're using the \s-1POST\s0 method, create your own user agent and encode
the content appropriately.
.PP
.Vb 2
\&    use HTTP::Request::Common qw(POST);
\&    use LWP::UserAgent;
\&
\&    $ua = LWP::UserAgent\->new();
\&    my $req = POST \*(Aqhttp://www.perl.com/cgi\-bin/cpan_mod\*(Aq,
\&                   [ module => \*(AqDB_File\*(Aq, readme => 1 ];
\&    $content = $ua\->request($req)\->as_string;
.Ve
.Sh "How do I decode or create those %\-encodings on the web?"
.IX Subsection "How do I decode or create those %-encodings on the web?"
If you are writing a \s-1CGI\s0 script, you should be using the \s-1CGI\s0.pm module
that comes with perl, or some other equivalent module.  The \s-1CGI\s0 module
automatically decodes queries for you, and provides an \fIescape()\fR
function to handle encoding.
.PP
The best source of detailed information on \s-1URI\s0 encoding is \s-1RFC\s0 2396.
Basically, the following substitutions do it:
.PP
.Vb 1
\&    s/([^\ew()\*(Aq*~!.\-])/sprintf \*(Aq%%%02x\*(Aq, ord $1/eg;   # encode
\&
\&    s/%([A\-Fa\-f\ed]{2})/chr hex $1/eg;                # decode
\&        s/%([[:xdigit:]]{2})/chr hex $1/eg;          # same thing
.Ve
.PP
However, you should only apply them to individual \s-1URI\s0 components, not
the entire \s-1URI\s0, otherwise you'll lose information and generally mess
things up.  If that didn't explain it, don't worry.  Just go read
section 2 of the \s-1RFC\s0, it's probably the best explanation there is.
.PP
\&\s-1RFC\s0 2396 also contains a lot of other useful information, including a
regexp for breaking any arbitrary \s-1URI\s0 into components (Appendix B).
.Sh "How do I redirect to another page?"
.IX Subsection "How do I redirect to another page?"
Specify the complete \s-1URL\s0 of the destination (even if it is on the same
server). This is one of the two different kinds of \s-1CGI\s0 \*(L"Location:\*(R"
responses which are defined in the \s-1CGI\s0 specification for a Parsed Headers
script. The other kind (an absolute URLpath) is resolved internally to
the server without any \s-1HTTP\s0 redirection. The \s-1CGI\s0 specifications do not
allow relative URLs in either case.
.PP
Use of \s-1CGI\s0.pm is strongly recommended.  This example shows redirection
with a complete \s-1URL\s0. This redirection is handled by the web browser.
.PP
.Vb 1
\&      use CGI qw/:standard/;
\&
\&      my $url = \*(Aqhttp://www.cpan.org/\*(Aq;
\&      print redirect($url);
.Ve
.PP
This example shows a redirection with an absolute URLpath.  This
redirection is handled by the local web server.
.PP
.Vb 2
\&      my $url = \*(Aq/CPAN/index.html\*(Aq;
\&      print redirect($url);
.Ve
.PP
But if coded directly, it could be as follows (the final \*(L"\en\*(R" is
shown separately, for clarity), using either a complete \s-1URL\s0 or
an absolute URLpath.
.PP
.Vb 2
\&      print "Location: $url\en";   # CGI response header
\&      print "\en";                 # end of headers
.Ve
.Sh "How do I put a password on my web pages?"
.IX Subsection "How do I put a password on my web pages?"
To enable authentication for your web server, you need to configure
your web server.  The configuration is different for different sorts
of web servers\*(--apache does it differently from iPlanet which does
it differently from \s-1IIS\s0.  Check your web server documentation for
the details for your particular server.
.Sh "How do I edit my .htpasswd and .htgroup files with Perl?"
.IX Subsection "How do I edit my .htpasswd and .htgroup files with Perl?"
The HTTPD::UserAdmin and HTTPD::GroupAdmin modules provide a
consistent \s-1OO\s0 interface to these files, regardless of how they're
stored.  Databases may be text, dbm, Berkeley \s-1DB\s0 or any database with
a \s-1DBI\s0 compatible driver.  HTTPD::UserAdmin supports files used by the
\&\*(L"Basic\*(R" and \*(L"Digest\*(R" authentication schemes.  Here's an example:
.PP
.Vb 4
\&    use HTTPD::UserAdmin ();
\&    HTTPD::UserAdmin
\&          \->new(DB => "/foo/.htpasswd")
\&          \->add($username => $password);
.Ve
.Sh "How do I make sure users can't enter values into a form that cause my \s-1CGI\s0 script to do bad things?"
.IX Subsection "How do I make sure users can't enter values into a form that cause my CGI script to do bad things?"
See the security references listed in the \s-1CGI\s0 Meta \s-1FAQ\s0
.PP
.Vb 1
\&        http://www.perl.org/CGI_MetaFAQ.html
.Ve
.Sh "How do I parse a mail header?"
.IX Subsection "How do I parse a mail header?"
For a quick-and-dirty solution, try this solution derived
from \*(L"split\*(R" in perlfunc:
.PP
.Vb 4
\&    $/ = \*(Aq\*(Aq;
\&    $header = <MSG>;
\&    $header =~ s/\en\es+/ /g;      # merge continuation lines
\&    %head = ( UNIX_FROM_LINE, split /^([\-\ew]+):\es*/m, $header );
.Ve
.PP
That solution doesn't do well if, for example, you're trying to
maintain all the Received lines.  A more complete approach is to use
the Mail::Header module from \s-1CPAN\s0 (part of the MailTools package).
.Sh "How do I decode a \s-1CGI\s0 form?"
.IX Subsection "How do I decode a CGI form?"
(contributed by brian d foy)
.PP
Use the \s-1CGI\s0.pm module that comes with Perl.  It's quick,
it's easy, and it actually does quite a bit of work to
ensure things happen correctly.  It handles \s-1GET\s0, \s-1POST\s0, and
\&\s-1HEAD\s0 requests, multipart forms, multivalued fields, query
string and message body combinations, and many other things
you probably don't want to think about.
.PP
It doesn't get much easier: the \s-1CGI\s0 module automatically
parses the input and makes each value available through the
\&\f(CW\*(C`param()\*(C'\fR function.
.PP
.Vb 1
\&        use CGI qw(:standard);
\&
\&        my $total = param( \*(Aqprice\*(Aq ) + param( \*(Aqshipping\*(Aq );
\&
\&        my @items = param( \*(Aqitem\*(Aq ); # multiple values, same field name
.Ve
.PP
If you want an object-oriented approach, \s-1CGI\s0.pm can do that too.
.PP
.Vb 1
\&        use CGI;
\&
\&        my $cgi = CGI\->new();
\&
\&        my $total = $cgi\->param( \*(Aqprice\*(Aq ) + $cgi\->param( \*(Aqshipping\*(Aq );
\&
\&        my @items = $cgi\->param( \*(Aqitem\*(Aq );
.Ve
.PP
You might also try CGI::Minimal which is a lightweight version
of the same thing.  Other CGI::* modules on \s-1CPAN\s0 might work better
for you, too.
.PP
Many people try to write their own decoder (or copy one from
another program) and then run into one of the many \*(L"gotchas\*(R"
of the task.  It's much easier and less hassle to use \s-1CGI\s0.pm.
.Sh "How do I check a valid mail address?"
.IX Subsection "How do I check a valid mail address?"
(partly contributed by Aaron Sherman)
.PP
This isn't as simple a question as it sounds.  There are two parts:
.PP
a) How do I verify that an email address is correctly formatted?
.PP
b) How do I verify that an email address targets a valid recipient?