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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,

       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 appropriate.

       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
       Perl,但骨子里是 CGI之类的问题,如果 post到

       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

       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

           <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()

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

       收录在 CPAN里的 libwww-perl
       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 appropriately.

           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

             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

           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
       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 string.

       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).



       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

       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
       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 like:


           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,

       如何解码一个 MIME/BASE64 字符串?


           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

       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


       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`

       gethostbyname()这个系统呼叫来找出该机的 IP位址了(假定您的 DNS

           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 CPAN下载)虽比较复杂,但可用来上传、也能抓档案。

       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.