X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlfaq9.pod;h=fa9ef116737fef99d9865c002857d6c6aa97578a;hb=0c359e6f1f1b2532c7bc7180d33870b48256aaff;hp=4c701cafdea381965bab92904d4c3eb6006de119;hpb=0e06870bf080a38cda51c06c6612359afc2334e1;p=p5sagit%2Fp5-mst-13.2.git

diff --git a/pod/perlfaq9.pod b/pod/perlfaq9.pod
index 4c701ca..fa9ef11 100644
--- a/pod/perlfaq9.pod
+++ b/pod/perlfaq9.pod
@@ -1,72 +1,96 @@
 =head1 NAME
 
-perlfaq9 - Networking ($Revision: 1.26 $, $Date: 1999/05/23 16:08:30 $)
+perlfaq9 - Networking
 
 =head1 DESCRIPTION
 
 This section deals with questions related to networking, the internet,
 and a few on the web.
 
-=head2 My CGI script runs from the command line but not the browser.  (500 Server Error)
+=head2 What is the correct form of response from a CGI script?
 
-If you can demonstrate that you've read the following FAQs and that
-your problem isn't something simple that can be easily answered, you'll
-probably receive a courteous and useful reply to your question if you
-post it on comp.infosystems.www.authoring.cgi (if it's something to do
-with HTTP, HTML, or the CGI protocols).  Questions that appear to be Perl
-questions but are really CGI ones that are posted to comp.lang.perl.misc
-may not be so well received.
+(Alan Flavell <flavell+www@a5.ph.gla.ac.uk> answers...)
 
-The useful FAQs and related documents are:
+The Common Gateway Interface (CGI) specifies a software interface between
+a program ("CGI script") and a web server (HTTPD). It is not specific
+to Perl, and has its own FAQs and tutorials, and usenet group,
+comp.infosystems.www.authoring.cgi
 
-    CGI FAQ
-        http://www.webthing.com/tutorials/cgifaq.html
+The CGI specification is outlined in an informational RFC:
+http://www.ietf.org/rfc/rfc3875
 
-    Web FAQ
-        http://www.boutell.com/faq/
+Other relevant documentation listed in: http://www.perl.org/CGI_MetaFAQ.html
 
-    WWW Security FAQ
-        http://www.w3.org/Security/Faq/
+These Perl FAQs very selectively cover some CGI issues. However, Perl
+programmers are strongly advised to use the C<CGI.pm> module, to take care
+of the details for them.
 
-    HTTP Spec
-        http://www.w3.org/pub/WWW/Protocols/HTTP/
+The similarity between CGI response headers (defined in the CGI
+specification) and HTTP response headers (defined in the HTTP
+specification, RFC2616) is intentional, but can sometimes be confusing.
 
-    HTML Spec
-        http://www.w3.org/TR/REC-html40/
-        http://www.w3.org/pub/WWW/MarkUp/
+The CGI specification defines two kinds of script: the "Parsed Header"
+script, and the "Non Parsed Header" (NPH) script. Check your server
+documentation to see what it supports. "Parsed Header" scripts are
+simpler in various respects. The CGI specification allows any of the
+usual newline representations in the CGI response (it's the server's
+job to create an accurate HTTP response based on it). So "\n" written in
+text mode is technically correct, and recommended. NPH scripts are more
+tricky: they must put out a complete and accurate set of HTTP
+transaction response headers; the HTTP specification calls for records
+to be terminated with carriage-return and line-feed, i.e ASCII \015\012
+written in binary mode.
 
-    CGI Spec
-        http://www.w3.org/CGI/
+Using C<CGI.pm> gives excellent platform independence, including EBCDIC
+systems. C<CGI.pm> selects an appropriate newline representation
+(C<$CGI::CRLF>) and sets binmode as appropriate.
 
-    CGI Security FAQ
-        http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt
+=head2 My CGI script runs from the command line but not the browser.  (500 Server Error)
+
+Several things could be wrong.  You can go through the "Troubleshooting
+Perl CGI scripts" guide at
+
+	http://www.perl.org/troubleshooting_CGI.html
+
+If, after that, you can demonstrate that you've read the FAQs and that
+your problem isn't something simple that can be easily answered, you'll
+probably receive a courteous and useful reply to your question if you
+post it on comp.infosystems.www.authoring.cgi (if it's something to do
+with HTTP or the CGI protocols).  Questions that appear to be Perl
+questions but are really CGI ones that are posted to comp.lang.perl.misc
+are not so well received.
+
+The useful FAQs, related documents, and troubleshooting guides are
+listed in the CGI Meta FAQ:
+
+	http://www.perl.org/CGI_MetaFAQ.html
 
 =head2 How can I get better error messages from a CGI program?
 
-Use the CGI::Carp module.  It replaces C<warn> and C<die>, plus the
-normal Carp modules C<carp>, C<croak>, and C<confess> functions with
+Use the C<CGI::Carp> module.  It replaces C<warn> and C<die>, plus the
+normal C<Carp> modules C<carp>, C<croak>, and C<confess> functions with
 more verbose and safer versions.  It still sends them to the normal
 server error log.
 
-    use CGI::Carp;
-    warn "This is a complaint";
-    die "But this one is serious";
+	use CGI::Carp;
+	warn "This is a complaint";
+	die "But this one is serious";
 
-The following use of CGI::Carp also redirects errors to a file of your choice,
-placed in a BEGIN block to catch compile-time warnings as well:
+The following use of C<CGI::Carp> also redirects errors to a file of your choice,
+placed in a C<BEGIN> block to catch compile-time warnings as well:
 
-    BEGIN {
-        use CGI::Carp qw(carpout);
-        open(LOG, ">>/var/local/cgi-logs/mycgi-log")
-            or die "Unable to append to mycgi-log: $!\n";
-        carpout(*LOG);
-    }
+	BEGIN {
+		use CGI::Carp qw(carpout);
+		open(LOG, ">>/var/local/cgi-logs/mycgi-log")
+			or die "Unable to append to mycgi-log: $!\n";
+		carpout(*LOG);
+	}
 
 You can even arrange for fatal errors to go back to the client browser,
 which is nice for your own debugging, but might confuse the end user.
 
-    use CGI::Carp qw(fatalsToBrowser);
-    die "Bad error here";
+	use CGI::Carp qw(fatalsToBrowser);
+	die "Bad error here";
 
 Even if the error happens before you get the HTTP header out, the module
 will try to take care of this to avoid the dreaded server 500 errors.
@@ -76,9 +100,9 @@ stamp prepended.
 
 =head2 How do I remove HTML from a string?
 
-The most correct way (albeit not the fastest) is to use HTML::Parser
+The most correct way (albeit not the fastest) is to use C<HTML::Parser>
 from CPAN.  Another mostly correct
-way is to use HTML::FormatText which not only removes HTML but also
+way is to use C<HTML::FormatText> which not only removes HTML but also
 attempts to do a little simple formatting of the resulting plain text.
 
 Many folks attempt a simple-minded regular expression approach, like
@@ -89,326 +113,392 @@ entities--like C<&lt;> for example.
 
 Here's one "simple-minded" approach, that works for most files:
 
-    #!/usr/bin/perl -p0777
-    s/<(?:[^>'"]*|(['"]).*?\1)*>//gs
+	#!/usr/bin/perl -p0777
+	s/<(?:[^>'"]*|(['"]).*?\1)*>//gs
 
 If you want a more complete solution, see the 3-stage striphtml
 program in
-http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/striphtml.gz
+http://www.cpan.org/authors/Tom_Christiansen/scripts/striphtml.gz
 .
 
 Here are some tricky cases that you should think about when picking
 a solution:
 
-    <IMG SRC = "foo.gif" ALT = "A > B">
+	<IMG SRC = "foo.gif" ALT = "A > B">
 
-    <IMG SRC = "foo.gif"
+	<IMG SRC = "foo.gif"
 	 ALT = "A > B">
 
-    <!-- <A comment> -->
+	<!-- <A comment> -->
 
-    <script>if (a<b && a>c)</script>
+	<script>if (a<b && a>c)</script>
 
-    <# Just data #>
+	<# Just data #>
 
-    <![INCLUDE CDATA [ >>>>>>>>>>>> ]]>
+	<![INCLUDE CDATA [ >>>>>>>>>>>> ]]>
 
 If HTML comments include other tags, those solutions would also break
 on text like this:
 
-    <!-- This section commented out.
-        <B>You can't see me!</B>
-    -->
+	<!-- This section commented out.
+		<B>You can't see me!</B>
+	-->
 
 =head2 How do I extract URLs?
 
-A quick but imperfect approach is
+You can easily extract all sorts of URLs from HTML with
+C<HTML::SimpleLinkExtor> which handles anchors, images, objects,
+frames, and many other tags that can contain a URL.  If you need
+anything more complex, you can create your own subclass of
+C<HTML::LinkExtor> or C<HTML::Parser>.  You might even use
+C<HTML::SimpleLinkExtor> as an example for something specifically
+suited to your needs.
+
+You can use C<URI::Find> to extract URLs from an arbitrary text document.
+
+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 HREF and there are no other attributes.
+
+	#!/usr/bin/perl -n00
+	# qxurl - tchrist@perl.com
+	print "$2\n" while m{
+		< \s*
+		  A \s+ HREF \s* = \s* (["']) (.*?) \1
+		\s* >
+	}gsix;
 
-    #!/usr/bin/perl -n00
-    # qxurl - tchrist@perl.com
-    print "$2\n" while m{
-	< \s*
-	  A \s+ HREF \s* = \s* (["']) (.*?) \1
-	\s* >
-    }gsix;
+=head2 How do I download a file from the user's machine?  How do I open a file on another machine?
 
-This version does not adjust relative URLs, understand alternate
-bases, deal with HTML comments, deal with HREF and NAME attributes
-in the same tag, understand extra qualifiers like TARGET, or accept
-URLs themselves as arguments.  It also runs about 100x faster than a
-more "complete" solution using the LWP suite of modules, such as the
-http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/xurl.gz program.
+In this case, download means to use the file upload feature of HTML
+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 B<multipart/form-data> encoding.  The C<CGI.pm> module (which
+comes with Perl as part of the Standard Library) supports this in the
+C<start_multipart_form()> method, which isn't the same as the C<startform()>
+method.
 
-=head2 How do I download a file from the user's machine?  How do I open a file on another machine?
+See the section in the C<CGI.pm> documentation on file uploads for code
+examples and details.
 
-In the context of an HTML form, you can use what's known as
-B<multipart/form-data> encoding.  The CGI.pm module (available from
-CPAN) supports this in the start_multipart_form() method, which isn't
-the same as the startform() method.
+=head2 How do I make an HTML pop-up menu with Perl?
 
-=head2 How do I make a pop-up menu in HTML?
+(contributed by brian d foy)
 
-Use the B<< <SELECT> >> and B<< <OPTION> >> tags.  The CGI.pm
-module (available from CPAN) supports this widget, as well as many
-others, including some that it cleverly synthesizes on its own.
+The C<CGI.pm> module (which comes with Perl) has functions to create
+the HTML form widgets. See the C<CGI.pm> documentation for more
+examples.
+
+	use CGI qw/:standard/;
+	print header,
+		start_html('Favorite Animals'),
+
+		start_form,
+			"What's your favorite animal? ",
+		popup_menu(
+			-name   => 'animal',
+			-values => [ qw( Llama Alpaca Camel Ram ) ]
+			),
+		submit,
+
+		end_form,
+		end_html;
 
 =head2 How do I fetch an HTML file?
 
-One approach, if you have the lynx text-based HTML browser installed
-on your system, is this:
+(contributed by brian d foy)
+
+Use the libwww-perl distribution. The C<LWP::Simple> module can fetch web
+resources and give their content back to you as a string:
 
-    $html_code = `lynx -source $url`;
-    $text_data = `lynx -dump $url`;
+	use LWP::Simple qw(get);
 
-The libwww-perl (LWP) modules from CPAN provide a more powerful way
-to do this.  They don't require lynx, but like lynx, can still work
-through proxies:
+	my $html = get( "http://www.example.com/index.html" );
 
-    # simplest version
-    use LWP::Simple;
-    $content = get($URL);
+It can also store the resource directly in a file:
 
-    # or print HTML from a URL
-    use LWP::Simple;
-    getprint "http://www.linpro.no/lwp/";
+	use LWP::Simple qw(getstore);
 
-    # 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't fetch HTML from http://www.perl.com/";
-    $ascii = HTML::FormatText->new->format(parse_html($html));
-    print $ascii;
+	getstore( "http://www.example.com/index.html", "foo.html" );
+
+If you need to do something more complicated, you can use
+C<LWP::UserAgent> module to create your own user-agent (e.g. browser)
+to get the job done. If you want to simulate an interactive web
+browser, you can use the C<WWW::Mechanize> module.
 
 =head2 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 C<WWW::Mechanize>.  See its
+documentation for all the details.
+
 If you're submitting values using the GET method, create a URL and encode
 the form using the C<query_form> method:
 
-    use LWP::Simple;
-    use URI::URL;
+	use LWP::Simple;
+	use URI::URL;
 
-    my $url = url('http://www.perl.com/cgi-bin/cpan_mod');
-    $url->query_form(module => 'DB_File', readme => 1);
-    $content = get($url);
+	my $url = url('http://www.perl.com/cgi-bin/cpan_mod');
+	$url->query_form(module => 'DB_File', readme => 1);
+	$content = get($url);
 
 If you're using the POST method, create your own user agent and encode
 the content appropriately.
 
-    use HTTP::Request::Common qw(POST);
-    use LWP::UserAgent;
+	use HTTP::Request::Common qw(POST);
+	use LWP::UserAgent;
 
-    $ua = LWP::UserAgent->new();
-    my $req = POST 'http://www.perl.com/cgi-bin/cpan_mod',
-                   [ module => 'DB_File', readme => 1 ];
-    $content = $ua->request($req)->as_string;
+	$ua = LWP::UserAgent->new();
+	my $req = POST 'http://www.perl.com/cgi-bin/cpan_mod',
+				   [ module => 'DB_File', readme => 1 ];
+	$content = $ua->request($req)->as_string;
 
 =head2 How do I decode or create those %-encodings on the web?
+X<URI> X<CGI.pm> X<CGI> X<URI::Escape> X<RFC 2396>
+
+(contributed by brian d foy)
+
+Those C<%> encodings handle reserved characters in URIs, as described
+in RFC 2396, Section 2. This encoding replaces the reserved character
+with the hexadecimal representation of the character's number from
+the US-ASCII table. For instance, a colon, C<:>, becomes C<%3A>.
+
+In CGI scripts, you don't have to worry about decoding URIs if you are
+using C<CGI.pm>. You shouldn't have to process the URI yourself,
+either on the way in or the way out.
+
+If you have to encode a string yourself, remember that you should
+never try to encode an already-composed URI. You need to escape the
+components separately then put them together. To encode a string, you
+can use the the C<URI::Escape> module. The C<uri_escape> function
+returns the escaped string:
+
+	my $original = "Colon : Hash # Percent %";
+
+	my $escaped = uri_escape( $original );
+
+	print "$escaped\n"; # 'Colon%20%3A%20Hash%20%23%20Percent%20%25'
+
+To decode the string, use the C<uri_unescape> function:
+
+	my $unescaped = uri_unescape( $escaped );
+
+	print $unescaped; # back to original
 
-Here's an example of decoding:
+If you wanted to do it yourself, you simply need to replace the
+reserved characters with their encodings. A global substitution
+is one way to do it:
 
-    $string = "http://altavista.digital.com/cgi-bin/query?pg=q&what=news&fmt=.&q=%2Bcgi-bin+%2Bperl.exe";
-    $string =~ s/%([a-fA-F0-9]{2})/chr(hex($1))/ge;
+	# encode
+	$string =~ s/([^^A-Za-z0-9\-_.!~*'()])/ sprintf "%%%0x", ord $1 /eg;
 
-Encoding is a bit harder, because you can't just blindly change
-all characters that are not letters, digits or underscores (C<\W>)
-into their hex escapes.
-It's important that characters with special meaning like C</> and C<?>
-I<not> be translated.  Probably the easiest way to get this right is
-to avoid reinventing the wheel and just use the URI::Escape module,
-available from CPAN.
+	#decode
+	$string =~ s/%([A-Fa-f\d]{2})/chr hex $1/eg;
 
 =head2 How do I redirect to another page?
 
-According to RFC 2616, "Hypertext Transfer Protocol -- HTTP/1.1", the
-preferred method is to send a C<Location:> header instead of a
-C<Content-Type:> header:
+Specify the complete URL of the destination (even if it is on the same
+server). This is one of the two different kinds of CGI "Location:"
+responses which are defined in the CGI specification for a Parsed Headers
+script. The other kind (an absolute URLpath) is resolved internally to
+the server without any HTTP redirection. The CGI specifications do not
+allow relative URLs in either case.
 
-    Location: http://www.domain.com/newpage
+Use of C<CGI.pm> is strongly recommended.  This example shows redirection
+with a complete URL. This redirection is handled by the web browser.
 
-Note that relative URLs in these headers can cause strange effects
-because of "optimizations" that servers do.
+	use CGI qw/:standard/;
 
-    $url = "http://www.perl.com/CPAN/";
-    print "Location: $url\n\n";
-    exit;
+	my $url = 'http://www.cpan.org/';
+	print redirect($url);
 
-To target a particular frame in a frameset, include the "Window-target:"
-in the header.
+This example shows a redirection with an absolute URLpath.  This
+redirection is handled by the local web server.
 
-    print <<EOF;
-    Location: http://www.domain.com/newpage
-    Window-target: <FrameName>
+	my $url = '/CPAN/index.html';
+	print redirect($url);
 
-    EOF
+But if coded directly, it could be as follows (the final "\n" is
+shown separately, for clarity), using either a complete URL or
+an absolute URLpath.
 
-To be correct to the spec, each of those virtual newlines should
-really be physical C<"\015\012"> sequences by the time your message is
-received by the client browser.  Except for NPH scripts, though, that
-local newline should get translated by your server into standard form,
-so you shouldn't have a problem here, even if you are stuck on MacOS.
-Everybody else probably won't even notice.
+	print "Location: $url\n";   # CGI response header
+	print "\n";                 # end of headers
 
 =head2 How do I put a password on my web pages?
 
-That depends.  You'll need to read the documentation for your web
-server, or perhaps check some of the other FAQs referenced above.
+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 IIS.  Check your web server documentation for
+the details for your particular server.
 
 =head2 How do I edit my .htpasswd and .htgroup files with Perl?
 
-The HTTPD::UserAdmin and HTTPD::GroupAdmin modules provide a
+The C<HTTPD::UserAdmin> and C<HTTPD::GroupAdmin> modules provide a
 consistent OO interface to these files, regardless of how they're
-stored.  Databases may be text, dbm, Berkley DB or any database with a
-DBI compatible driver.  HTTPD::UserAdmin supports files used by the
-`Basic' and `Digest' authentication schemes.  Here's an example:
+stored.  Databases may be text, dbm, Berkeley DB or any database with
+a DBI compatible driver.  C<HTTPD::UserAdmin> supports files used by the
+"Basic" and "Digest" authentication schemes.  Here's an example:
 
-    use HTTPD::UserAdmin ();
-    HTTPD::UserAdmin
+	use HTTPD::UserAdmin ();
+	HTTPD::UserAdmin
 	  ->new(DB => "/foo/.htpasswd")
 	  ->add($username => $password);
 
 =head2 How do I make sure users can't enter values into a form that cause my CGI script to do bad things?
 
-Read the CGI security FAQ, at
-http://www-genome.wi.mit.edu/WWW/faqs/www-security-faq.html , and the
-Perl/CGI FAQ at
-http://www.perl.com/CPAN/doc/FAQs/cgi/perl-cgi-faq.html .
+See the security references listed in the CGI Meta FAQ
 
-In brief: use tainting (see L<perlsec>), which makes sure that data
-from outside your script (eg, CGI parameters) are never used in
-C<eval> or C<system> calls.  In addition to tainting, never use the
-single-argument form of system() or exec().  Instead, supply the
-command and arguments as a list, which prevents shell globbing.
+	http://www.perl.org/CGI_MetaFAQ.html
 
 =head2 How do I parse a mail header?
 
 For a quick-and-dirty solution, try this solution derived
 from L<perlfunc/split>:
 
-    $/ = '';
-    $header = <MSG>;
-    $header =~ s/\n\s+/ /g;	 # merge continuation lines
-    %head = ( UNIX_FROM_LINE, split /^([-\w]+):\s*/m, $header );
+	$/ = '';
+	$header = <MSG>;
+	$header =~ s/\n\s+/ /g;	 # merge continuation lines
+	%head = ( UNIX_FROM_LINE, split /^([-\w]+):\s*/m, $header );
 
 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 CPAN (part of the MailTools package).
+the C<Mail::Header> module from CPAN (part of the C<MailTools> package).
 
 =head2 How do I decode a CGI form?
 
-You use a standard module, probably CGI.pm.  Under no circumstances
-should you attempt to do so by hand!
-
-You'll see a lot of CGI programs that blindly read from STDIN the number
-of bytes equal to CONTENT_LENGTH for POSTs, or grab QUERY_STRING for
-decoding GETs.  These programs are very poorly written.  They only work
-sometimes.  They typically forget to check the return value of the read()
-system call, which is a cardinal sin.  They don't handle HEAD requests.
-They don't handle multipart forms used for file uploads.  They don't deal
-with GET/POST combinations where query fields are in more than one place.
-They don't deal with keywords in the query string.
-
-In short, they're bad hacks.  Resist them at all costs.  Please do not be
-tempted to reinvent the wheel.  Instead, use the CGI.pm or CGI_Lite.pm
-(available from CPAN), or if you're trapped in the module-free land
-of perl1 .. perl4, you might look into cgi-lib.pl (available from
-http://cgi-lib.stanford.edu/cgi-lib/ ).
-
-Make sure you know whether to use a GET or a POST in your form.
-GETs should only be used for something that doesn't update the server.
-Otherwise you can get mangled databases and repeated feedback mail
-messages.  The fancy word for this is ``idempotency''.  This simply
-means that there should be no difference between making a GET request
-for a particular URL once or multiple times.  This is because the
-HTTP protocol definition says that a GET request may be cached by the
-browser, or server, or an intervening proxy.  POST requests cannot be
-cached, because each request is independent and matters.  Typically,
-POST requests change or depend on state on the server (query or update
-a database, send mail, or purchase a computer).
+(contributed by brian d foy)
+
+Use the C<CGI.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 GET, POST, and
+HEAD requests, multipart forms, multivalued fields, query
+string and message body combinations, and many other things
+you probably don't want to think about.
+
+It doesn't get much easier: the C<CGI.pm> module automatically
+parses the input and makes each value available through the
+C<param()> function.
+
+	use CGI qw(:standard);
+
+	my $total = param( 'price' ) + param( 'shipping' );
+
+	my @items = param( 'item' ); # multiple values, same field name
+
+If you want an object-oriented approach, C<CGI.pm> can do that too.
+
+	use CGI;
+
+	my $cgi = CGI->new();
+
+	my $total = $cgi->param( 'price' ) + $cgi->param( 'shipping' );
+
+	my @items = $cgi->param( 'item' );
+
+You might also try C<CGI::Minimal> which is a lightweight version
+of the same thing.  Other CGI::* modules on CPAN might work better
+for you, too.
+
+Many people try to write their own decoder (or copy one from
+another program) and then run into one of the many "gotchas"
+of the task.  It's much easier and less hassle to use C<CGI.pm>.
 
 =head2 How do I check a valid mail address?
 
-You can't, at least, not in real time.  Bummer, eh?
+(partly contributed by Aaron Sherman)
 
-Without sending mail to the address and seeing whether there's a human
-on the other hand to answer you, you cannot determine whether a mail
-address is valid.  Even if you apply the mail header standard, you
-can have problems, because there are deliverable addresses that aren't
-RFC-822 (the mail header standard) compliant, and addresses that aren't
-deliverable which are compliant.
-
-Many are tempted to try to eliminate many frequently-invalid
-mail addresses with a simple regex, such as
-C</^[\w.-]+\@([\w.-]\.)+\w+$/>.  It's a very bad idea.  However,
-this also throws out many valid ones, and says nothing about
-potential deliverability, so is not suggested.  Instead, see
-http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/ckaddr.gz ,
-which actually checks against the full RFC spec (except for nested
-comments), looks for addresses you may not wish to accept mail to
-(say, Bill Clinton or your postmaster), and then makes sure that the
-hostname given can be looked up in the DNS MX records.  It's not fast,
-but it works for what it tries to do.
+This isn't as simple a question as it sounds.  There are two parts:
 
-Our best advice for verifying a person's mail address is to have them
-enter their address twice, just as you normally do to change a password.
-This usually weeds out typos.  If both versions match, send
-mail to that address with a personal message that looks somewhat like:
+a) How do I verify that an email address is correctly formatted?
 
-    Dear someuser@host.com,
+b) How do I verify that an email address targets a valid recipient?
 
-    Please confirm the mail address you gave us Wed May  6 09:38:41
-    MDT 1998 by replying to this message.  Include the string
-    "Rumpelstiltskin" in that reply, but spelled in reverse; that is,
-    start with "Nik...".  Once this is done, your confirmed address will
-    be entered into our records.
+Without sending mail to the address and seeing whether there's a human
+on the other end to answer you, you cannot fully answer part I<b>, but
+either the C<Email::Valid> or the C<RFC::RFC822::Address> module will do
+both part I<a> and part I<b> as far as you can in real-time.
+
+If you want to just check part I<a> to see that the address is valid
+according to the mail header standard with a simple regular expression,
+you can have problems, because there are deliverable addresses that
+aren't RFC-2822 (the latest mail header standard) compliant, and
+addresses that aren't deliverable which, are compliant.  However,  the
+following will match valid RFC-2822 addresses that do not have comments,
+folding whitespace, or any other obsolete or non-essential elements.
+This I<just> matches the address itself:
+
+	my $atom       = qr{[a-zA-Z0-9_!#\$\%&'*+/=?\^`{}~|\-]+};
+	my $dot_atom   = qr{$atom(?:\.$atom)*};
+	my $quoted     = qr{"(?:\\[^\r\n]|[^\\"])*"};
+	my $local      = qr{(?:$dot_atom|$quoted)};
+	my $quotedpair = qr{\\[\x00-\x09\x0B-\x0c\x0e-\x7e]};
+	my $domain_lit = qr{\[(?:$quotedpair|[\x21-\x5a\x5e-\x7e])*\]};
+ 	my $domain     = qr{(?:$dot_atom|$domain_lit)};
+	my $addr_spec  = qr{$local\@$domain};
+
+Just match an address against C</^${addr_spec}$/> to see if it follows
+the RFC2822 specification.  However, because it is impossible to be
+sure that such a correctly formed address is actually the correct way
+to reach a particular person or even has a mailbox associated with it,
+you must be very careful about how you use this.
 
-If you get the message back and they've followed your directions,
-you can be reasonably assured that it's real.
+Our best advice for verifying a person's mail address is to have them
+enter their address twice, just as you normally do to change a
+password. This usually weeds out typos. If both versions match, send
+mail to that address with a personal message. If you get the message
+back and they've followed your directions, you can be reasonably
+assured that it's real.
 
 A related strategy that's less open to forgery is to give them a PIN
 (personal ID number).  Record the address and PIN (best that it be a
-random one) for later processing.  In the mail you send, ask them to
+random one) for later processing. In the mail you send, ask them to
 include the PIN in their reply.  But if it bounces, or the message is
-included via a ``vacation'' script, it'll be there anyway.  So it's
+included via a "vacation" script, it'll be there anyway.  So it's
 best to ask them to mail back a slight alteration of the PIN, such as
 with the characters reversed, one added or subtracted to each digit, etc.
 
 =head2 How do I decode a MIME/BASE64 string?
 
-The MIME-tools package (available from CPAN) handles this and a lot
-more.  Decoding BASE64 becomes as simple as:
+The C<MIME-Base64> package (available from CPAN) handles this as well as
+the MIME/QP encoding.  Decoding BASE64 becomes as simple as:
 
-    use MIME::base64;
-    $decoded = decode_base64($encoded);
+	use MIME::Base64;
+	$decoded = decode_base64($encoded);
 
-A more direct approach is to use the unpack() function's "u"
+The C<MIME-Tools> package (available from CPAN) supports extraction with
+decoding of BASE64 encoded attachments and content directly from email
+messages.
+
+If the string to decode is short (less than 84 bytes long)
+a more direct approach is to use the C<unpack()> function's "u"
 format after minor transliterations:
 
-    tr#A-Za-z0-9+/##cd;                   # remove non-base64 chars
-    tr#A-Za-z0-9+/# -_#;                  # convert to uuencoded format
-    $len = pack("c", 32 + 0.75*length);   # compute length byte
-    print unpack("u", $len . $_);         # uudecode and print
+	tr#A-Za-z0-9+/##cd;                   # remove non-base64 chars
+	tr#A-Za-z0-9+/# -_#;                  # convert to uuencoded format
+	$len = pack("c", 32 + 0.75*length);   # compute length byte
+	print unpack("u", $len . $_);         # uudecode and print
 
 =head2 How do I return the user's mail address?
 
-On systems that support getpwuid, the $< variable, and the
-Sys::Hostname module (which is part of the standard perl distribution),
+On systems that support getpwuid, the C<< $< >> variable, and the
+C<Sys::Hostname> module (which is part of the standard perl distribution),
 you can probably try using something like this:
 
-    use Sys::Hostname;
-    $address = sprintf('%s@%s', scalar getpwuid($<), hostname);
+	use Sys::Hostname;
+	$address = sprintf('%s@%s', scalar getpwuid($<), hostname);
 
 Company policies on mail address can mean that this generates addresses
 that the company's mail system will not accept, so you should ask for
 users' mail addresses when this matters.  Furthermore, not all systems
 on which Perl runs are so forthcoming with this information as is Unix.
 
-The Mail::Util module from CPAN (part of the MailTools package) provides a
-mailaddress() function that tries to guess the mail address of the user.
+The C<Mail::Util> module from CPAN (part of the C<MailTools> package) provides a
+C<mailaddress()> function that tries to guess the mail address of the user.
 It makes a more intelligent guess than the code above, using information
 given when the module was installed, but it could still be incorrect.
 Again, the best way is often just to ask the user.
@@ -417,135 +507,173 @@ Again, the best way is often just to ask the user.
 
 Use the C<sendmail> program directly:
 
-    open(SENDMAIL, "|/usr/lib/sendmail -oi -t -odq")
-                        or die "Can't fork for sendmail: $!\n";
-    print SENDMAIL <<"EOF";
-    From: User Originating Mail <me\@host>
-    To: Final Destination <you\@otherhost>
-    Subject: A relevant subject line
+	open(SENDMAIL, "|/usr/lib/sendmail -oi -t -odq")
+		or die "Can't fork for sendmail: $!\n";
+	print SENDMAIL <<"EOF";
+	From: User Originating Mail <me\@host>
+	To: Final Destination <you\@otherhost>
+	Subject: A relevant subject line
 
-    Body of the message goes here after the blank line
-    in as many lines as you like.
-    EOF
-    close(SENDMAIL)     or warn "sendmail didn't close nicely";
+	Body of the message goes here after the blank line
+	in as many lines as you like.
+	EOF
+	close(SENDMAIL)     or warn "sendmail didn't close nicely";
 
-The B<-oi> option prevents sendmail from interpreting a line consisting
+The B<-oi> option prevents C<sendmail> from interpreting a line consisting
 of a single dot as "end of message".  The B<-t> option says to use the
 headers to decide who to send the message to, and B<-odq> says to put
 the message into the queue.  This last option means your message won't
 be immediately delivered, so leave it out if you want immediate
 delivery.
 
-Alternate, less convenient approaches include calling mail (sometimes
-called mailx) directly or simply opening up port 25 have having an
+Alternate, less convenient approaches include calling C<mail> (sometimes
+called C<mailx>) directly or simply opening up port 25 have having an
 intimate conversation between just you and the remote SMTP daemon,
-probably sendmail.
+probably C<sendmail>.
+
+Or you might be able use the CPAN module C<Mail::Mailer>:
+
+	use Mail::Mailer;
+
+	$mailer = Mail::Mailer->new();
+	$mailer->open({ From    => $from_address,
+					To      => $to_address,
+					Subject => $subject,
+				  })
+		or die "Can't open: $!\n";
+	print $mailer $body;
+	$mailer->close();
+
+The C<Mail::Internet> module uses C<Net::SMTP> which is less Unix-centric than
+C<Mail::Mailer>, but less reliable.  Avoid raw SMTP commands.  There
+are many reasons to use a mail transport agent like C<sendmail>.  These
+include queuing, MX records, and security.
+
+=head2 How do I use MIME to make an attachment to a mail message?
+
+This answer is extracted directly from the C<MIME::Lite> documentation.
+Create a multipart message (i.e., one with attachments).
+
+	use MIME::Lite;
 
-Or you might be able use the CPAN module Mail::Mailer:
+	### Create a new multipart message:
+	$msg = MIME::Lite->new(
+				 From    =>'me@myhost.com',
+				 To      =>'you@yourhost.com',
+				 Cc      =>'some@other.com, some@more.com',
+				 Subject =>'A message with 2 parts...',
+				 Type    =>'multipart/mixed'
+				 );
 
-    use Mail::Mailer;
+	### Add parts (each "attach" has same arguments as "new"):
+	$msg->attach(Type     =>'TEXT',
+				 Data     =>"Here's the GIF file you wanted"
+				 );
+	$msg->attach(Type     =>'image/gif',
+				 Path     =>'aaa000123.gif',
+				 Filename =>'logo.gif'
+				 );
 
-    $mailer = Mail::Mailer->new();
-    $mailer->open({ From    => $from_address,
-                    To      => $to_address,
-                    Subject => $subject,
-                  })
-        or die "Can't open: $!\n";
-    print $mailer $body;
-    $mailer->close();
+	$text = $msg->as_string;
 
-The Mail::Internet module uses Net::SMTP which is less Unix-centric than
-Mail::Mailer, but less reliable.  Avoid raw SMTP commands.  There
-are many reasons to use a mail transport agent like sendmail.  These
-include queueing, MX records, and security.
+C<MIME::Lite> also includes a method for sending these things.
+
+	$msg->send;
+
+This defaults to using L<sendmail> but can be customized to use
+SMTP via L<Net::SMTP>.
 
 =head2 How do I read mail?
 
-While you could use the Mail::Folder module from CPAN (part of the
-MailFolder package) or the Mail::Internet module from CPAN (also part
-of the MailTools package), often a module is overkill.  Here's a
+While you could use the C<Mail::Folder> module from CPAN (part of the
+C<MailFolder> package) or the C<Mail::Internet> module from CPAN (part
+of the C<MailTools> package), often a module is overkill.  Here's a
 mail sorter.
 
-    #!/usr/bin/perl
-    # bysub1 - simple sort by subject
-    my(@msgs, @sub);
-    my $msgno = -1;
-    $/ = '';                    # paragraph reads
-    while (<>) {
-        if (/^From/m) {
-            /^Subject:\s*(?:Re:\s*)*(.*)/mi;
-            $sub[++$msgno] = lc($1) || '';
-        }
-        $msgs[$msgno] .= $_;
-    }
-    for my $i (sort { $sub[$a] cmp $sub[$b] || $a <=> $b } (0 .. $#msgs)) {
-        print $msgs[$i];
-    }
+	#!/usr/bin/perl
+
+	my(@msgs, @sub);
+	my $msgno = -1;
+	$/ = '';                    # paragraph reads
+	while (<>) {
+		if (/^From /m) {
+			/^Subject:\s*(?:Re:\s*)*(.*)/mi;
+			$sub[++$msgno] = lc($1) || '';
+		}
+		$msgs[$msgno] .= $_;
+	}
+	for my $i (sort { $sub[$a] cmp $sub[$b] || $a <=> $b } (0 .. $#msgs)) {
+		print $msgs[$i];
+	}
 
 Or more succinctly,
 
-    #!/usr/bin/perl -n00
-    # bysub2 - awkish sort-by-subject
-    BEGIN { $msgno = -1 }
-    $sub[++$msgno] = (/^Subject:\s*(?:Re:\s*)*(.*)/mi)[0] if /^From/m;
-    $msg[$msgno] .= $_;
-    END { print @msg[ sort { $sub[$a] cmp $sub[$b] || $a <=> $b } (0 .. $#msg) ] }
+	#!/usr/bin/perl -n00
+	# bysub2 - awkish sort-by-subject
+	BEGIN { $msgno = -1 }
+	$sub[++$msgno] = (/^Subject:\s*(?:Re:\s*)*(.*)/mi)[0] if /^From/m;
+	$msg[$msgno] .= $_;
+	END { print @msg[ sort { $sub[$a] cmp $sub[$b] || $a <=> $b } (0 .. $#msg) ] }
+
+=head2 How do I find out my hostname, domainname, or IP address?
+X<hostname, domainname, IP address, host, domain, hostfqdn, inet_ntoa,
+gethostbyname, Socket, Net::Domain, Sys::Hostname>
+
+(contributed by brian d foy)
 
-=head2 How do I find out my hostname/domainname/IP address?
+The C<Net::Domain> module, which is part of the standard distribution starting
+in perl5.7.3, can get you the fully qualified domain name (FQDN), the host
+name, or the domain name.
 
-The normal way to find your own hostname is to call the C<`hostname`>
-program.  While sometimes expedient, this has some problems, such as
-not knowing whether you've got the canonical name or not.  It's one of
-those tradeoffs of convenience versus portability.
+	use Net::Domain qw(hostname hostfqdn hostdomain);
 
-The Sys::Hostname module (part of the standard perl distribution) will
-give you the hostname after which you can find out the IP address
-(assuming you have working DNS) with a gethostbyname() call.
+	my $host = hostfqdn();
 
-    use Socket;
-    use Sys::Hostname;
-    my $host = hostname();
-    my $addr = inet_ntoa(scalar gethostbyname($host || 'localhost'));
+The C<Sys::Hostname> module, included in the standard distribution since
+perl5.6, can also get the hostname.
 
-Probably the simplest way to learn your DNS domain name is to grok
-it out of /etc/resolv.conf, at least under Unix.  Of course, this
-assumes several things about your resolv.conf configuration, including
-that it exists.
+	use Sys::Hostname;
 
-(We still need a good DNS domain name-learning method for non-Unix
-systems.)
+	$host = hostname();
+
+To get the IP address, you can use the C<gethostbyname> built-in function
+to turn the name into a number. To turn that number into the dotted octet
+form (a.b.c.d) that most people expect, use the C<inet_ntoa> function
+from the C<Socket> module, which also comes with perl.
+
+	use Socket;
+
+	my $address = inet_ntoa(
+		scalar gethostbyname( $host || 'localhost' )
+		);
 
 =head2 How do I fetch a news article or the active newsgroups?
 
-Use the Net::NNTP or News::NNTPClient modules, both available from CPAN.
+Use the C<Net::NNTP> or C<News::NNTPClient> modules, both available from CPAN.
 This can make tasks like fetching the newsgroup list as simple as
 
-    perl -MNews::NNTPClient
-      -e 'print News::NNTPClient->new->list("newsgroups")'
+	perl -MNews::NNTPClient
+	  -e 'print News::NNTPClient->new->list("newsgroups")'
 
 =head2 How do I fetch/put an FTP file?
 
-LWP::Simple (available from CPAN) can fetch but not put.  Net::FTP (also
+C<LWP::Simple> (available from CPAN) can fetch but not put.  C<Net::FTP> (also
 available from CPAN) is more complex but can put as well as fetch.
 
 =head2 How can I do RPC in Perl?
 
-A DCE::RPC module is being developed (but is not yet available) and
-will be released as part of the DCE-Perl package (available from
-CPAN).  The rpcgen suite, available from CPAN/authors/id/JAKE/, is
-an RPC stub generator and includes an RPC::ONC module.
+(Contributed by brian d foy)
+
+Use one of the RPC modules you can find on CPAN (
+http://search.cpan.org/search?query=RPC&mode=all ).
 
 =head1 AUTHOR AND COPYRIGHT
 
-Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.
-All rights reserved.
+Copyright (c) 1997-2010 Tom Christiansen, Nathan Torkington, and
+other authors as noted. All rights reserved.
 
-When included as part of the Standard Version of Perl, or as part of
-its complete documentation whether printed or otherwise, this work
-may be distributed only under the terms of Perl's Artistic License.
-Any distribution of this file or derivatives thereof I<outside>
-of that package require that special arrangements be made with
-copyright holder.
+This documentation is free; you can redistribute it and/or modify it
+under the same terms as Perl itself.
 
 Irrespective of its distribution, all code examples in this file
 are hereby placed into the public domain.  You are permitted and