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       perlfaq9 - 网络 (2003/01/31 17:36:57 )


       网络通信,互联网以及少量有关 web 的内容

       What is the correct form of response from a CGI script?

       (Alan Flavell <> answers...)

       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

       The original CGI specification is at:

       Current best-practice RFC draft at: http://CGI-Spec.Golux.Com/

       Other relevant documentation listed in:

       These Perl FAQs very selectively cover some CGI issues. However, Perl programmers are
       strongly advised to use the module, to take care of the details for them.

       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.

       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.

       Using gives excellent platform independence, including EBCDIC systems.
       selects an appropriate newline representation ($CGI::CRLF) and sets binmode as

       我的 CGI 脚本从命令行执行正常,但是在浏览器中不行 (500 Server Error)。

       可能有很多事错了。可以仔细阅读 "Troubleshooting Perl CGI scripts" guide, 位置是


       如果接下来,你能证明你已阅读了 FAQ
       并且你的问题不是那么简单,非叁言两语即可回答的话,那麽您 post到
       comp.infosystems.www.authoring.cgi上(如果是有关 HTTP 、 HTML ,或
       CGI通信协定)的问题可能也会得到口气和缓而有用的答覆。表面上看似 Perl,但骨子里是
       CGI之类的问题,如果 post到 comp.lang.perl.misc人家可能就不会这麽乐意地接受了。

       几个实用的 FAQ,相关文档和查错向导列在 CGI Meta FAQ 中:


       如何从 CGI 程序中得到好一点的错误提示?

       Use the CGI::Carp module.  It replaces "warn" and "die", plus the normal Carp modules
       "carp", "croak", and "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";

       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:

           BEGIN {
               use CGI::Carp qw(carpout);
               open(LOG, ">>/var/local/cgi-logs/mycgi-log")
                   or die "Unable to append to mycgi-log: $!\n";

       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";

       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.  Normal warnings still go out to the
       server error log (or wherever you've sent them with "carpout") with the application name
       and date stamp prepended.

       如何将字符串中的 HTML 删除?

       最正确(尽管不是最快)的方法是使用 HTML::Parse模组(可由 CPAN取得,是所有写
       Web程式者必备的 libwww-perl 套件的一部分)。另一中最正确的办法是使用
       HTML::FormatText,它不仅删除了 HTML,同时也试图对结果文本进行简单的格式化。

       quote【跳脱】的箭头号,或有 HTML comment出现;再加上一些疏忽,譬如,人们常忘了转换如 < 的
       entities(跳脱字 元"&lt;")。


           #!/usr/bin/perl -p0777

       如果您想要更完整的解法,请看叁部曲的 striphtml 程式, .

       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">

           <!-- <A comment> -->

           <script>if (a<b && a>c)</script>

           <# Just data #>

           <![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>

       如何萃取 URL?

       可以简单地从 HTML 中得到所有种类的 URL,只要使用 "HTML::SimpleLinkExtor"
       模块,它可以处理锚,图像,对象,桢,其他包含 URL 的标签。如果需要更复杂的东西,可以创建
       "HTML::LinkExtor" 的子类或使用 "HTML::Parser". 你甚至可以用 "HTML::SimpleLinkExtor"

       You can use 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 -
               print "$2\n" while m{
                   < \s*
                     A \s+ HREF \s* = \s* (["']) (.*?) \1
                   \s* >


       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 multipart/form-data encoding.  The module (which comes with Perl as
       part of the Standard Library) supports this in the start_multipart_form() method, which
       isn't the same as the startform() method.

       See the section in the documentation on file uploads for code examples and details.

       如何在 HTML 添加一个弹出菜单?

       用 <SELECT> 和 <OPTION>这两个标签。 CGI.pm模组(可由 CPAN取得)对这个

       如何获取 HTML 文件?

       有一个方法是,如果您的系统上装有 lynx一类的文字模式的 HTML浏览器的话,那麽可以这麽做:

           $html_code = `lynx -source $url`;
           $text_data = `lynx -dump $url`;

       收录在 CPAN里的 libwww-perl (LWP)模组则提供了更强的方法来做这件事。它不但可钻过
       proxies,而且也不需要 lynx:

           # simplest version
           use LWP::Simple;
           $content = get($URL);

           # or print HTML from a URL
           use LWP::Simple;
           getprint "";

           # 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("");
           defined $html
               or die "Can't fetch HTML from";
           $ascii = HTML::FormatText->new->format(parse_html($html));
           print $ascii;

       如何根据提交的内容自动生成一个 HTML ?

       If you're submitting values using the GET method, create a URL and encode the form using
       the "query_form" method:

           use LWP::Simple;
           use URI::URL;

           my $url = url('');
           $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

           use HTTP::Request::Common qw(POST);
           use LWP::UserAgent;

           $ua = LWP::UserAgent->new();
           my $req = POST '',
                          [ module => 'DB_File', readme => 1 ];
           $content = $ua->request($req)->as_string;

       如何解码或创建 web 中的 %-encoding?

       If you are writing a CGI script, you should be using the module that comes with
       perl, or some other equivalent module.  The CGI module automatically decodes queries for
       you, and provides an escape() function to handle encoding.

       The best source of detailed information on URI encoding is RFC 2396.  Basically, the
       following substitutions do it:

           s/([^\w()'*~!.-])/sprintf '%%%02x', ord $1/eg;   # encode

           s/%([A-Fa-f\d]{2})/chr hex $1/eg;            # decode

       However, you should only apply them to individual URI components, not the entire URI,
       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 RFC, it's probably the best explanation
       there is.

       RFC 2396 also contains a lot of other useful information, including a regexp for breaking
       any arbitrary URI into components (Appendix B).


       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.

       Use of is strongly recommended.  This example shows redirection with a complete
       URL. This redirection is handled by the web browser.

             use CGI qw/:standard/;

             my $url = '';
             print redirect($url);

       This example shows a redirection with an absolute URLpath.  This redirection is handled by
       the local web server.

             my $url = '/CPAN/index.html';
             print redirect($url);

       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.

             print "Location: $url\n";   # CGI response header
             print "\n";                 # end of headers


       要启用 web 服务器的验证,你需要配置你的 web 服务器,不同的服务器有不同的方法---apache 与
       iPlanet 不同,后者又与 IIS 不同。从你的 web 服务器的文档中查找特定服务器的配置细节。

       如何用 Perl 修改我的 .htpasswd  .htgroup 文件?

       HTTPD::UserAdmin 和 HTTPD::GroupAdmin
       dbm、Berkeley DB或任何 DBI相容的资料库驱动程式 (drivers)。 HTTPD::UserAdmin支援`Basic' 和
       `Digest'这两个认证模式所用的档案。以下是 一例:

           use HTTPD::UserAdmin ();
                 ->new(DB => "/foo/.htpasswd")
                 ->add($username => $password);

       如何确保用户不会在表单中输入使我的 CGI 脚本作坏事的值?

       阅读 CGI Meta FAQ 列出的安全索引



       要使用一个快速的方法,可以这样使用 perlfunc 中的 "split" 函数:

           $/ = '';
           $header = <MSG>;
           $header =~ s/\n\s+/ /g;      # 将延续行合并成单行
           %head = ( UNIX_FROM_LINE, split /^([-\w]+):\s*/m, $header );

       但是,如果您若想保留所有 Received栏位资料的话【因 Received
       栏位通常不止一个】,这个解法便不太行了。一个完整的解法是使用收录在 CPAN的 Mail::Header
       模组( MailTools 套件的一部分)。

       如何解码一个 CGI 表单?


       你大概都看过一大堆从 STDIN 读取与 $ENV{CONTENT_LENGTH} 长度相同的字节,或者获取
       $ENV{QUERY_STRING} 来解码 GET。这些程序都非常糟糕。他们仅在某些时候工作。他们通常不检查
       read() 的返回值,这是主要的错误。他们不处理 HEAD
       请求。他们不处理文件上载时的多成分表单。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

       In short, they're bad hacks.  Resist them at all costs.  Please do not be tempted to
       reinvent the wheel.  Instead, use the or (available from CPAN), or if
       you're trapped in the module-free land of perl1 .. perl4, you might look into
       (available from ).

       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).



       email 标头的标准规格来做检查的依据,您还是有可能会遇到问题,因为有些送得到的位址并不 符合
       RFC-822(电子邮件标头的标准)的规定,但有些符合标准的位址却无法投 递。

       You can use the Email::Valid or RFC::RFC822::Address which check the format of the
       address, although they cannot actually tell you if it is a deliverable address (i.e. that
       mail to the address will not bounce).  Modules like Mail::CheckUser and Mail::EXPN try to
       interact with the domain name system or particular mail servers to learn even more, but
       their methods do not work everywhere---especially for security conscious administrators.

       许多人试图用一个简单的正规表示式,例如 "/^[\w.-]+\@(?:[\w-]+\.)+\w+$/"
       来消除一些通常是无效的 email
       位址。不过,这样做也把很多合格的位址给一起滤掉了,而且对测试一个位址有没有希望投递成功完全没有帮助,所以在此建议大家不要这麽做;不过您可以看看: , 这个
       script真的彻底地依据所有的 RFC规定来做检验(除了内嵌式
       comments外),同时会排除一些您可能不会想送信去的位址(如 Bill Clinton【美国总统】或您的
       postmaster),然後它会确定位址中的主机名称可在 DNS中找得到。这个 script

       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


           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.

       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 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 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.

       如何解码一个 MIME/BASE64 字符串?

       MIME-tools套件(可自 CPAN取得)不但可处理这个问题而且有许多其他的功能。有了这个套件,解

           use MIME::Base64;
           $decoded = decode_base64($encoded);

       The MIME-Tools package (available from CPAN) supports extraction with decoding of BASE64
       encoded attachments and content directly from email messages.

       一个比较直接的解法是先做一点简单的转译,然後使用 unpack()这个函数的 ``u'' 格式:

           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


       On systems that support getpwuid, the $< variable, and the 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);

       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.  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.


       Use the "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

           Body of the message goes here after the blank line
           in as many lines as you like.
           close(SENDMAIL)     or warn "sendmail didn't close nicely";

       The -oi option prevents sendmail from interpreting a line consisting of a single dot as
       "end of message".  The -t option says to use the headers to decide who to send the message
       to, and -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 intimate conversation between just
       you and the remote SMTP daemon, probably sendmail.

       Or you might be able use the CPAN module 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;

       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 queuing, MX records, and security.

       如何使用 MIME 来为邮件消息增加附件?

       This answer is extracted directly from the MIME::Lite documentation.  Create a multipart
       message (i.e., one with attachments).

           use MIME::Lite;

           ### Create a new multipart message:
           $msg = MIME::Lite->new(
                        From    =>'',
                        To      =>'',
                        Cc      =>',',
                        Subject =>'A message with 2 parts...',
                        Type    =>'multipart/mixed'

           ### 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'

           $text = $msg->as_string;

       MIME::Lite also includes a method for sending these things.


       This defaults to using sendmail but can be customized to use SMTP via Net::SMTP.


       While you could use the Mail::Folder module from CPAN (part of the MailFolder package) or
       the Mail::Internet module from CPAN (part of the MailTools package), often a module is
       overkill.  Here's a mail sorter.


           my(@msgs, @sub);
           my $msgno = -1;
           $/ = '';                    # paragraph reads
           while (<>) {
               if (/^From /m) {
                   $sub[++$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) ] }

       如何找到我的主机名/域名/IP 地址?

       长久以来许多 code都很草率地直接呼叫 `hostname`

       Sys::Hostname这个模组(标准 perl发行的一部分)可用来取得机器的名字,然後您便可利用
       gethostbyname()这个系统呼叫来找出该机的 IP位址了(假定您的 DNS 运作正常)。

           use Socket;
           use Sys::Hostname;
           my $host = hostname();
           my $addr = inet_ntoa(scalar gethostbyname($host ⎪⎪ 'localhost'));

       至少在 Unix 底下,取得 DNS网域名最简单的方法大概要算是直接从 /etc/resolv.conf
       这个档案里面找。当然,这麽做的前提是 resolv.conf

       (Perl在非 Unix系统下尚需要一有效的方法来测出机器和网域名)


       使用 Net::NNTP或 News::NNTPClient模组,两者皆可自

           perl -MNews::NNTPClient
             -e 'print News::NNTPClient->new->list("newsgroups")'

       如何获取/上传一个 FTP 文件?

       LWP::Simple模组(可自 CPAN下载)可以抓,但不能上传档案。 Net::FTP模组(也可自

       如何进行远程过程调用 RPC ?

       模块 DCE::RPC 正在开发中 (但是还不可用),将成为 DCE-Perl 包 (可以从 CPAN 下载)
       的一部分。rpcgen 套件,可以从 CPAN/authors/id/JAKE/ 找到,是一个 RPC 存根生成器,包含一个
       RPC::ONC 模块。


       Copyright (c) 1997-2002 Tom Christiansen and Nathan Torkington.  All rights reserved.

       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 encouraged to use this code in your own programs
       for fun or for profit as you see fit.  A simple comment in the code giving credit would be
       courteous but is not required.