mingw/html/pod/perlfaq9.html

   1 <?xml version="1.0" ?>
   2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
   3 <html xmlns="http://www.w3.org/1999/xhtml">
   4 <head>
   5 <title>perlfaq9 - Networking</title>
   6 <meta http-equiv="content-type" content="text/html; charset=utf-8" />
   7 <link rev="made" href="mailto:" />
   8 </head>
   9
  10 <body style="background-color: white">
  11 <table border="0" width="100%" cellspacing="0" cellpadding="3">
  12 <tr><td class="block" style="background-color: #cccccc" valign="middle">
  13 <big><strong><span class="block">&nbsp;perlfaq9 - Networking</span></strong></big>
  14 </td></tr>
  15 </table>
  16
  17 <p><a name="__index__"></a></p>
  18 <!-- INDEX BEGIN -->
  19
  20 <ul>
  21
  22         <li><a href="#name">NAME</a></li>
  23         <li><a href="#description">DESCRIPTION</a></li>
  24         <ul>
  25
  26                 <li><a href="#what_is_the_correct_form_of_response_from_a_cgi_script">What is the correct form of response from a CGI script?</a></li>
  27                 <li><a href="#my_cgi_script_runs_from_the_command_line_but_not_the_browser___500_server_error_">My CGI script runs from the command line but not the browser.  (500 Server Error)</a></li>
  28                 <li><a href="#how_can_i_get_better_error_messages_from_a_cgi_program">How can I get better error messages from a CGI program?</a></li>
  29                 <li><a href="#how_do_i_remove_html_from_a_string">How do I remove HTML from a string?</a></li>
  30                 <li><a href="#how_do_i_extract_urls">How do I extract URLs?</a></li>
  31                 <li><a href="#how_do_i_download_a_file_from_the_user_s_machine_how_do_i_open_a_file_on_another_machine">How do I download a file from the user's machine?  How do I open a file on another machine?</a></li>
  32                 <li><a href="#how_do_i_make_a_popup_menu_in_html">How do I make a pop-up menu in HTML?</a></li>
  33                 <li><a href="#how_do_i_fetch_an_html_file">How do I fetch an HTML file?</a></li>
  34                 <li><a href="#how_do_i_automate_an_html_form_submission">How do I automate an HTML form submission?</a></li>
  35                 <li><a href="#how_do_i_decode_or_create_those__encodings_on_the_web">How do I decode or create those %-encodings on the web?</a></li>
  36                 <li><a href="#how_do_i_redirect_to_another_page">How do I redirect to another page?</a></li>
  37                 <li><a href="#how_do_i_put_a_password_on_my_web_pages">How do I put a password on my web pages?</a></li>
  38                 <li><a href="#how_do_i_edit_my__htpasswd_and__htgroup_files_with_perl">How do I edit my .htpasswd and .htgroup files with Perl?</a></li>
  39                 <li><a href="#how_do_i_make_sure_users_can_t_enter_values_into_a_form_that_cause_my_cgi_script_to_do_bad_things">How do I make sure users can't enter values into a form that cause my CGI script to do bad things?</a></li>
  40                 <li><a href="#how_do_i_parse_a_mail_header">How do I parse a mail header?</a></li>
  41                 <li><a href="#how_do_i_decode_a_cgi_form">How do I decode a CGI form?</a></li>
  42                 <li><a href="#how_do_i_check_a_valid_mail_address">How do I check a valid mail address?</a></li>
  43                 <li><a href="#how_do_i_decode_a_mime_base64_string">How do I decode a MIME/BASE64 string?</a></li>
  44                 <li><a href="#how_do_i_return_the_user_s_mail_address">How do I return the user's mail address?</a></li>
  45                 <li><a href="#how_do_i_send_mail">How do I send mail?</a></li>
  46                 <li><a href="#how_do_i_use_mime_to_make_an_attachment_to_a_mail_message">How do I use MIME to make an attachment to a mail message?</a></li>
  47                 <li><a href="#how_do_i_read_mail">How do I read mail?</a></li>
  48                 <li><a href="#how_do_i_find_out_my_hostname__domainname__or_ip_address">How do I find out my hostname, domainname, or IP address?</a></li>
  49                 <li><a href="#how_do_i_fetch_a_news_article_or_the_active_newsgroups">How do I fetch a news article or the active newsgroups?</a></li>
  50                 <li><a href="#how_do_i_fetch_put_an_ftp_file">How do I fetch/put an FTP file?</a></li>
  51                 <li><a href="#how_can_i_do_rpc_in_perl">How can I do RPC in Perl?</a></li>
  52         </ul>
  53
  54         <li><a href="#author_and_copyright">AUTHOR AND COPYRIGHT</a></li>
  55 </ul>
  56 <!-- INDEX END -->
  57
  58 <hr />
  59 <p>
  60 </p>
  61 <h1><a name="name">NAME</a></h1>
  62 <p>perlfaq9 - Networking ($Revision: 1.28 $, $Date: 2005/12/31 00:54:37 $)</p>
  63 <p>
  64 </p>
  65 <hr />
  66 <h1><a name="description">DESCRIPTION</a></h1>
  67 <p>This section deals with questions related to networking, the internet,
  68 and a few on the web.</p>
  69 <p>
  70 </p>
  71 <h2><a name="what_is_the_correct_form_of_response_from_a_cgi_script">What is the correct form of response from a CGI script?</a></h2>
  72 <p>(Alan Flavell &lt;<a href="mailto:flavell+www@a5.ph.gla.ac.uk">flavell+www@a5.ph.gla.ac.uk</a>&gt; answers...)</p>
  73 <p>The Common Gateway Interface (CGI) specifies a software interface between
  74 a program (``CGI script'') and a web server (HTTPD). It is not specific
  75 to Perl, and has its own FAQs and tutorials, and usenet group,
  76 comp.infosystems.www.authoring.cgi</p>
  77 <p>The CGI specification is outlined in an informational RFC:
  78 <a href="http://www.ietf.org/rfc/rfc3875">http://www.ietf.org/rfc/rfc3875</a></p>
  79 <p>Other relevant documentation listed in: <a href="http://www.perl.org/CGI_MetaFAQ.html">http://www.perl.org/CGI_MetaFAQ.html</a></p>
  80 <p>These Perl FAQs very selectively cover some CGI issues. However, Perl
  81 programmers are strongly advised to use the CGI.pm module, to take care
  82 of the details for them.</p>
  83 <p>The similarity between CGI response headers (defined in the CGI
  84 specification) and HTTP response headers (defined in the HTTP
  85 specification, RFC2616) is intentional, but can sometimes be confusing.</p>
  86 <p>The CGI specification defines two kinds of script: the ``Parsed Header''
  87 script, and the ``Non Parsed Header'' (NPH) script. Check your server
  88 documentation to see what it supports. ``Parsed Header'' scripts are
  89 simpler in various respects. The CGI specification allows any of the
  90 usual newline representations in the CGI response (it's the server's
  91 job to create an accurate HTTP response based on it). So ``\n'' written in
  92 text mode is technically correct, and recommended. NPH scripts are more
  93 tricky: they must put out a complete and accurate set of HTTP
  94 transaction response headers; the HTTP specification calls for records
  95 to be terminated with carriage-return and line-feed, i.e ASCII \015\012
  96 written in binary mode.</p>
  97 <p>Using CGI.pm gives excellent platform independence, including EBCDIC
  98 systems. CGI.pm selects an appropriate newline representation
  99 ($CGI::CRLF) and sets binmode as appropriate.</p>
 100 <p>
 101 </p>
 102 <h2><a name="my_cgi_script_runs_from_the_command_line_but_not_the_browser___500_server_error_">My CGI script runs from the command line but not the browser.  (500 Server Error)</a></h2>
 103 <p>Several things could be wrong.  You can go through the ``Troubleshooting
 104 Perl CGI scripts'' guide at</p>
 105 <pre>
 106         <a href="http://www.perl.org/troubleshooting_CGI.html">http://www.perl.org/troubleshooting_CGI.html</a></pre>
 107 <p>If, after that, you can demonstrate that you've read the FAQs and that
 108 your problem isn't something simple that can be easily answered, you'll
 109 probably receive a courteous and useful reply to your question if you
 110 post it on comp.infosystems.www.authoring.cgi (if it's something to do
 111 with HTTP or the CGI protocols).  Questions that appear to be Perl
 112 questions but are really CGI ones that are posted to comp.lang.perl.misc
 113 are not so well received.</p>
 114 <p>The useful FAQs, related documents, and troubleshooting guides are
 115 listed in the CGI Meta FAQ:</p>
 116 <pre>
 117         <a href="http://www.perl.org/CGI_MetaFAQ.html">http://www.perl.org/CGI_MetaFAQ.html</a></pre>
 118 <p>
 119 </p>
 120 <h2><a name="how_can_i_get_better_error_messages_from_a_cgi_program">How can I get better error messages from a CGI program?</a></h2>
 121 <p>Use the CGI::Carp module.  It replaces <code>warn</code> and <code>die</code>, plus the
 122 normal Carp modules <code>carp</code>, <code>croak</code>, and <code>confess</code> functions with
 123 more verbose and safer versions.  It still sends them to the normal
 124 server error log.</p>
 125 <pre>
 126     use CGI::Carp;
 127     warn &quot;This is a complaint&quot;;
 128     die &quot;But this one is serious&quot;;</pre>
 129 <p>The following use of CGI::Carp also redirects errors to a file of your choice,
 130 placed in a BEGIN block to catch compile-time warnings as well:</p>
 131 <pre>
 132     BEGIN {
 133         use CGI::Carp qw(carpout);
 134         open(LOG, &quot;&gt;&gt;/var/local/cgi-logs/mycgi-log&quot;)
 135             or die &quot;Unable to append to mycgi-log: $!\n&quot;;
 136         carpout(*LOG);
 137     }</pre>
 138 <p>You can even arrange for fatal errors to go back to the client browser,
 139 which is nice for your own debugging, but might confuse the end user.</p>
 140 <pre>
 141     use CGI::Carp qw(fatalsToBrowser);
 142     die &quot;Bad error here&quot;;</pre>
 143 <p>Even if the error happens before you get the HTTP header out, the module
 144 will try to take care of this to avoid the dreaded server 500 errors.
 145 Normal warnings still go out to the server error log (or wherever
 146 you've sent them with <code>carpout</code>) with the application name and date
 147 stamp prepended.</p>
 148 <p>
 149 </p>
 150 <h2><a name="how_do_i_remove_html_from_a_string">How do I remove HTML from a string?</a></h2>
 151 <p>The most correct way (albeit not the fastest) is to use HTML::Parser
 152 from CPAN.  Another mostly correct
 153 way is to use HTML::FormatText which not only removes HTML but also
 154 attempts to do a little simple formatting of the resulting plain text.</p>
 155 <p>Many folks attempt a simple-minded regular expression approach, like
 156 <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_s_"><code>s/&lt;.*?&gt;//g</code></a>, but that fails in many cases because the tags
 157 may continue over line breaks, they may contain quoted angle-brackets,
 158 or HTML comment may be present.  Plus, folks forget to convert
 159 entities--like <code>&amp;lt;</code> for example.</p>
 160 <p>Here's one ``simple-minded'' approach, that works for most files:</p>
 161 <pre>
 162     #!/usr/bin/perl -p0777
 163     s/&lt;(?:[^&gt;'&quot;]*|(['&quot;]).*?\1)*&gt;//gs</pre>
 164 <p>If you want a more complete solution, see the 3-stage striphtml
 165 program in
 166 <a href="http://www.cpan.org/authors/Tom_Christiansen/scripts/striphtml.gz">http://www.cpan.org/authors/Tom_Christiansen/scripts/striphtml.gz</a>
 167 .</p>
 168 <p>Here are some tricky cases that you should think about when picking
 169 a solution:</p>
 170 <pre>
 171     &lt;IMG SRC = &quot;foo.gif&quot; ALT = &quot;A &gt; B&quot;&gt;</pre>
 172 <pre>
 173     &lt;IMG SRC = &quot;foo.gif&quot;
 174          ALT = &quot;A &gt; B&quot;&gt;</pre>
 175 <pre>
 176     &lt;!-- &lt;A comment&gt; --&gt;</pre>
 177 <pre>
 178     &lt;script&gt;if (a&lt;b &amp;&amp; a&gt;c)&lt;/script&gt;</pre>
 179 <pre>
 180     &lt;# Just data #&gt;</pre>
 181 <pre>
 182     &lt;![INCLUDE CDATA [ &gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt; ]]&gt;</pre>
 183 <p>If HTML comments include other tags, those solutions would also break
 184 on text like this:</p>
 185 <pre>
 186     &lt;!-- This section commented out.
 187         &lt;B&gt;You can't see me!&lt;/B&gt;
 188     --&gt;</pre>
 189 <p>
 190 </p>
 191 <h2><a name="how_do_i_extract_urls">How do I extract URLs?</a></h2>
 192 <p>You can easily extract all sorts of URLs from HTML with
 193 <code>HTML::SimpleLinkExtor</code> which handles anchors, images, objects,
 194 frames, and many other tags that can contain a URL.  If you need
 195 anything more complex, you can create your own subclass of
 196 <code>HTML::LinkExtor</code> or <code>HTML::Parser</code>.  You might even use
 197 <code>HTML::SimpleLinkExtor</code> as an example for something specifically
 198 suited to your needs.</p>
 199 <p>You can use URI::Find to extract URLs from an arbitrary text document.</p>
 200 <p>Less complete solutions involving regular expressions can save
 201 you a lot of processing time if you know that the input is simple.  One
 202 solution from Tom Christiansen runs 100 times faster than most
 203 module based approaches but only extracts URLs from anchors where the first
 204 attribute is HREF and there are no other attributes.</p>
 205 <pre>
 206         #!/usr/bin/perl -n00
 207         # qxurl - tchrist@perl.com
 208         print &quot;$2\n&quot; while m{
 209             &lt; \s*
 210               A \s+ HREF \s* = \s* ([&quot;']) (.*?) \1
 211             \s* &gt;
 212         }gsix;</pre>
 213 <p>
 214 </p>
 215 <h2><a name="how_do_i_download_a_file_from_the_user_s_machine_how_do_i_open_a_file_on_another_machine">How do I download a file from the user's machine?  How do I open a file on another machine?</a></h2>
 216 <p>In this case, download means to use the file upload feature of HTML
 217 forms.  You allow the web surfer to specify a file to send to your web
 218 server.  To you it looks like a download, and to the user it looks
 219 like an upload.  No matter what you call it, you do it with what's
 220 known as <strong>multipart/form-data</strong> encoding.  The CGI.pm module (which
 221 comes with Perl as part of the Standard Library) supports this in the
 222 <code>start_multipart_form()</code> method, which isn't the same as the <code>startform()</code>
 223 method.</p>
 224 <p>See the section in the CGI.pm documentation on file uploads for code
 225 examples and details.</p>
 226 <p>
 227 </p>
 228 <h2><a name="how_do_i_make_a_popup_menu_in_html">How do I make a pop-up menu in HTML?</a></h2>
 229 <p>Use the <strong>&lt;SELECT</strong> &gt;&gt; and <strong>&lt;OPTION</strong> &gt;&gt; tags.  The CGI.pm
 230 module (available from CPAN) supports this widget, as well as many
 231 others, including some that it cleverly synthesizes on its own.</p>
 232 <p>
 233 </p>
 234 <h2><a name="how_do_i_fetch_an_html_file">How do I fetch an HTML file?</a></h2>
 235 <p>One approach, if you have the lynx text-based HTML browser installed
 236 on your system, is this:</p>
 237 <pre>
 238     $html_code = `lynx -source $url`;
 239     $text_data = `lynx -dump $url`;</pre>
 240 <p>The libwww-perl (LWP) modules from CPAN provide a more powerful way
 241 to do this.  They don't require lynx, but like lynx, can still work
 242 through proxies:</p>
 243 <pre>
 244     # simplest version
 245     use LWP::Simple;
 246     $content = get($URL);</pre>
 247 <pre>
 248     # or print HTML from a URL
 249     use LWP::Simple;
 250     getprint &quot;<a href="http://www.linpro.no/lwp/&quot">http://www.linpro.no/lwp/&quot</a>;;</pre>
 251 <pre>
 252     # or print ASCII from HTML from a URL
 253     # also need HTML-Tree package from CPAN
 254     use LWP::Simple;
 255     use HTML::Parser;
 256     use HTML::FormatText;
 257     my ($html, $ascii);
 258     $html = get(&quot;<a href="http://www.perl.com/&quot">http://www.perl.com/&quot</a>;);
 259     defined $html
 260         or die &quot;Can't fetch HTML from <a href="http://www.perl.com/&quot">http://www.perl.com/&quot</a>;;
 261     $ascii = HTML::FormatText-&gt;new-&gt;format(parse_html($html));
 262     print $ascii;</pre>
 263 <p>
 264 </p>
 265 <h2><a name="how_do_i_automate_an_html_form_submission">How do I automate an HTML form submission?</a></h2>
 266 <p>If you are doing something complex, such as moving through many pages
 267 and forms or a web site, you can use <code>WWW::Mechanize</code>.  See its
 268 documentation for all the details.</p>
 269 <p>If you're submitting values using the GET method, create a URL and encode
 270 the form using the <code>query_form</code> method:</p>
 271 <pre>
 272     use LWP::Simple;
 273     use URI::URL;</pre>
 274 <pre>
 275     my $url = url('<a href="http://www.perl.com/cgi-bin/cpan_mod">http://www.perl.com/cgi-bin/cpan_mod</a>');
 276     $url-&gt;query_form(module =&gt; 'DB_File', readme =&gt; 1);
 277     $content = get($url);</pre>
 278 <p>If you're using the POST method, create your own user agent and encode
 279 the content appropriately.</p>
 280 <pre>
 281     use HTTP::Request::Common qw(POST);
 282     use LWP::UserAgent;</pre>
 283 <pre>
 284     $ua = LWP::UserAgent-&gt;new();
 285     my $req = POST '<a href="http://www.perl.com/cgi-bin/cpan_mod">http://www.perl.com/cgi-bin/cpan_mod</a>',
 286                    [ module =&gt; 'DB_File', readme =&gt; 1 ];
 287     $content = $ua-&gt;request($req)-&gt;as_string;</pre>
 288 <p>
 289 </p>
 290 <h2><a name="how_do_i_decode_or_create_those__encodings_on_the_web">How do I decode or create those %-encodings on the web?</a></h2>
 291 <p>If you are writing a CGI script, you should be using the CGI.pm module
 292 that comes with perl, or some other equivalent module.  The CGI module
 293 automatically decodes queries for you, and provides an <code>escape()</code>
 294 function to handle encoding.</p>
 295 <p>The best source of detailed information on URI encoding is RFC 2396.
 296 Basically, the following substitutions do it:</p>
 297 <pre>
 298     s/([^\w()'*~!.-])/sprintf '%%%02x', ord $1/eg;   # encode</pre>
 299 <pre>
 300     s/%([A-Fa-f\d]{2})/chr hex $1/eg;                # decode
 301         s/%([[:xdigit:]]{2})/chr hex $1/eg;          # same thing</pre>
 302 <p>However, you should only apply them to individual URI components, not
 303 the entire URI, otherwise you'll lose information and generally mess
 304 things up.  If that didn't explain it, don't worry.  Just go read
 305 section 2 of the RFC, it's probably the best explanation there is.</p>
 306 <p>RFC 2396 also contains a lot of other useful information, including a
 307 regexp for breaking any arbitrary URI into components (Appendix B).</p>
 308 <p>
 309 </p>
 310 <h2><a name="how_do_i_redirect_to_another_page">How do I redirect to another page?</a></h2>
 311 <p>Specify the complete URL of the destination (even if it is on the same
 312 server). This is one of the two different kinds of CGI ``Location:''
 313 responses which are defined in the CGI specification for a Parsed Headers
 314 script. The other kind (an absolute URLpath) is resolved internally to
 315 the server without any HTTP redirection. The CGI specifications do not
 316 allow relative URLs in either case.</p>
 317 <p>Use of CGI.pm is strongly recommended.  This example shows redirection
 318 with a complete URL. This redirection is handled by the web browser.</p>
 319 <pre>
 320       use CGI qw/:standard/;</pre>
 321 <pre>
 322       my $url = '<a href="http://www.cpan.org/">http://www.cpan.org/</a>';
 323       print redirect($url);</pre>
 324 <p>This example shows a redirection with an absolute URLpath.  This
 325 redirection is handled by the local web server.</p>
 326 <pre>
 327       my $url = '/CPAN/index.html';
 328       print redirect($url);</pre>
 329 <p>But if coded directly, it could be as follows (the final ``\n'' is
 330 shown separately, for clarity), using either a complete URL or
 331 an absolute URLpath.</p>
 332 <pre>
 333       print &quot;Location: $url\n&quot;;   # CGI response header
 334       print &quot;\n&quot;;                 # end of headers</pre>
 335 <p>
 336 </p>
 337 <h2><a name="how_do_i_put_a_password_on_my_web_pages">How do I put a password on my web pages?</a></h2>
 338 <p>To enable authentication for your web server, you need to configure
 339 your web server.  The configuration is different for different sorts
 340 of web servers---apache does it differently from iPlanet which does
 341 it differently from IIS.  Check your web server documentation for
 342 the details for your particular server.</p>
 343 <p>
 344 </p>
 345 <h2><a name="how_do_i_edit_my__htpasswd_and__htgroup_files_with_perl">How do I edit my .htpasswd and .htgroup files with Perl?</a></h2>
 346 <p>The HTTPD::UserAdmin and HTTPD::GroupAdmin modules provide a
 347 consistent OO interface to these files, regardless of how they're
 348 stored.  Databases may be text, dbm, Berkeley DB or any database with
 349 a DBI compatible driver.  HTTPD::UserAdmin supports files used by the
 350 ``Basic'' and ``Digest'' authentication schemes.  Here's an example:</p>
 351 <pre>
 352     use HTTPD::UserAdmin ();
 353     HTTPD::UserAdmin
 354           -&gt;new(DB =&gt; &quot;/foo/.htpasswd&quot;)
 355           -&gt;add($username =&gt; $password);</pre>
 356 <p>
 357 </p>
 358 <h2><a name="how_do_i_make_sure_users_can_t_enter_values_into_a_form_that_cause_my_cgi_script_to_do_bad_things">How do I make sure users can't enter values into a form that cause my CGI script to do bad things?</a></h2>
 359 <p>See the security references listed in the CGI Meta FAQ</p>
 360 <pre>
 361         <a href="http://www.perl.org/CGI_MetaFAQ.html">http://www.perl.org/CGI_MetaFAQ.html</a></pre>
 362 <p>
 363 </p>
 364 <h2><a name="how_do_i_parse_a_mail_header">How do I parse a mail header?</a></h2>
 365 <p>For a quick-and-dirty solution, try this solution derived
 366 from <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_split">split in the perlfunc manpage</a>:</p>
 367 <pre>
 368     $/ = '';
 369     $header = &lt;MSG&gt;;
 370     $header =~ s/\n\s+/ /g;      # merge continuation lines
 371     %head = ( UNIX_FROM_LINE, split /^([-\w]+):\s*/m, $header );</pre>
 372 <p>That solution doesn't do well if, for example, you're trying to
 373 maintain all the Received lines.  A more complete approach is to use
 374 the Mail::Header module from CPAN (part of the MailTools package).</p>
 375 <p>
 376 </p>
 377 <h2><a name="how_do_i_decode_a_cgi_form">How do I decode a CGI form?</a></h2>
 378 <p>(contributed by brian d foy)</p>
 379 <p>Use the CGI.pm module that comes with Perl.  It's quick,
 380 it's easy, and it actually does quite a bit of work to
 381 ensure things happen correctly.  It handles GET, POST, and
 382 HEAD requests, multipart forms, multivalued fields, query
 383 string and message body combinations, and many other things
 384 you probably don't want to think about.</p>
 385 <p>It doesn't get much easier: the CGI module automatically
 386 parses the input and makes each value available through the
 387 <code>param()</code> function.</p>
 388 <pre>
 389         use CGI qw(:standard);</pre>
 390 <pre>
 391         my $total = param( 'price' ) + param( 'shipping' );</pre>
 392 <pre>
 393         my @items = param( 'item' ); # multiple values, same field name</pre>
 394 <p>If you want an object-oriented approach, CGI.pm can do that too.</p>
 395 <pre>
 396         use CGI;</pre>
 397 <pre>
 398         my $cgi = CGI-&gt;new();</pre>
 399 <pre>
 400         my $total = $cgi-&gt;param( 'price' ) + $cgi-&gt;param( 'shipping' );</pre>
 401 <pre>
 402         my @items = $cgi-&gt;param( 'item' );</pre>
 403 <p>You might also try CGI::Minimal which is a lightweight version
 404 of the same thing.  Other CGI::* modules on CPAN might work better
 405 for you, too.</p>
 406 <p>Many people try to write their own decoder (or copy one from
 407 another program) and then run into one of the many ``gotchas''
 408 of the task.  It's much easier and less hassle to use CGI.pm.</p>
 409 <p>
 410 </p>
 411 <h2><a name="how_do_i_check_a_valid_mail_address">How do I check a valid mail address?</a></h2>
 412 <p>You can't, at least, not in real time.  Bummer, eh?</p>
 413 <p>Without sending mail to the address and seeing whether there's a human
 414 on the other end to answer you, you cannot determine whether a mail
 415 address is valid.  Even if you apply the mail header standard, you
 416 can have problems, because there are deliverable addresses that aren't
 417 RFC-822 (the mail header standard) compliant, and addresses that aren't
 418 deliverable which are compliant.</p>
 419 <p>You can use the Email::Valid or RFC::RFC822::Address which check
 420 the format of the address, although they cannot actually tell you
 421 if it is a deliverable address (i.e. that mail to the address
 422 will not bounce).  Modules like Mail::CheckUser and Mail::EXPN
 423 try to interact with the domain name system or particular
 424 mail servers to learn even more, but their methods do not
 425 work everywhere---especially for security conscious administrators.</p>
 426 <p>Many are tempted to try to eliminate many frequently-invalid
 427 mail addresses with a simple regex, such as
 428 <code>/^[\w.-]+\@(?:[\w-]+\.)+\w+$/</code>.  It's a very bad idea.  However,
 429 this also throws out many valid ones, and says nothing about
 430 potential deliverability, so it is not suggested.  Instead, see
 431 <a href="http://www.cpan.org/authors/Tom_Christiansen/scripts/ckaddr.gz">http://www.cpan.org/authors/Tom_Christiansen/scripts/ckaddr.gz</a> ,
 432 which actually checks against the full RFC spec (except for nested
 433 comments), looks for addresses you may not wish to accept mail to
 434 (say, Bill Clinton or your postmaster), and then makes sure that the
 435 hostname given can be looked up in the DNS MX records.  It's not fast,
 436 but it works for what it tries to do.</p>
 437 <p>Our best advice for verifying a person's mail address is to have them
 438 enter their address twice, just as you normally do to change a password.
 439 This usually weeds out typos.  If both versions match, send
 440 mail to that address with a personal message that looks somewhat like:</p>
 441 <pre>
 442     Dear someuser@host.com,</pre>
 443 <pre>
 444     Please confirm the mail address you gave us Wed May  6 09:38:41
 445     MDT 1998 by replying to this message.  Include the string
 446     &quot;Rumpelstiltskin&quot; in that reply, but spelled in reverse; that is,
 447     start with &quot;Nik...&quot;.  Once this is done, your confirmed address will
 448     be entered into our records.</pre>
 449 <p>If you get the message back and they've followed your directions,
 450 you can be reasonably assured that it's real.</p>
 451 <p>A related strategy that's less open to forgery is to give them a PIN
 452 (personal ID number).  Record the address and PIN (best that it be a
 453 random one) for later processing.  In the mail you send, ask them to
 454 include the PIN in their reply.  But if it bounces, or the message is
 455 included via a ``vacation'' script, it'll be there anyway.  So it's
 456 best to ask them to mail back a slight alteration of the PIN, such as
 457 with the characters reversed, one added or subtracted to each digit, etc.</p>
 458 <p>
 459 </p>
 460 <h2><a name="how_do_i_decode_a_mime_base64_string">How do I decode a MIME/BASE64 string?</a></h2>
 461 <p>The MIME-Base64 package (available from CPAN) handles this as well as
 462 the MIME/QP encoding.  Decoding BASE64 becomes as simple as:</p>
 463 <pre>
 464     use MIME::Base64;
 465     $decoded = decode_base64($encoded);</pre>
 466 <p>The MIME-Tools package (available from CPAN) supports extraction with
 467 decoding of BASE64 encoded attachments and content directly from email
 468 messages.</p>
 469 <p>If the string to decode is short (less than 84 bytes long)
 470 a more direct approach is to use the <code>unpack()</code> function's ``u''
 471 format after minor transliterations:</p>
 472 <pre>
 473     tr#A-Za-z0-9+/##cd;                   # remove non-base64 chars
 474     tr#A-Za-z0-9+/# -_#;                  # convert to uuencoded format
 475     $len = pack(&quot;c&quot;, 32 + 0.75*length);   # compute length byte
 476     print unpack(&quot;u&quot;, $len . $_);         # uudecode and print</pre>
 477 <p>
 478 </p>
 479 <h2><a name="how_do_i_return_the_user_s_mail_address">How do I return the user's mail address?</a></h2>
 480 <p>On systems that support getpwuid, the $&lt; variable, and the
 481 Sys::Hostname module (which is part of the standard perl distribution),
 482 you can probably try using something like this:</p>
 483 <pre>
 484     use Sys::Hostname;
 485     $address = sprintf('%s@%s', scalar getpwuid($&lt;), hostname);</pre>
 486 <p>Company policies on mail address can mean that this generates addresses
 487 that the company's mail system will not accept, so you should ask for
 488 users' mail addresses when this matters.  Furthermore, not all systems
 489 on which Perl runs are so forthcoming with this information as is Unix.</p>
 490 <p>The Mail::Util module from CPAN (part of the MailTools package) provides a
 491 <code>mailaddress()</code> function that tries to guess the mail address of the user.
 492 It makes a more intelligent guess than the code above, using information
 493 given when the module was installed, but it could still be incorrect.
 494 Again, the best way is often just to ask the user.</p>
 495 <p>
 496 </p>
 497 <h2><a name="how_do_i_send_mail">How do I send mail?</a></h2>
 498 <p>Use the <code>sendmail</code> program directly:</p>
 499 <pre>
 500     open(SENDMAIL, &quot;|/usr/lib/sendmail -oi -t -odq&quot;)
 501                         or die &quot;Can't fork for sendmail: $!\n&quot;;
 502     print SENDMAIL &lt;&lt;&quot;EOF&quot;;
 503     From: User Originating Mail &lt;me\@host&gt;
 504     To: Final Destination &lt;you\@otherhost&gt;
 505     Subject: A relevant subject line</pre>
 506 <pre>
 507     Body of the message goes here after the blank line
 508     in as many lines as you like.
 509     EOF
 510     close(SENDMAIL)     or warn &quot;sendmail didn't close nicely&quot;;</pre>
 511 <p>The <strong>-oi</strong> option prevents sendmail from interpreting a line consisting
 512 of a single dot as ``end of message''.  The <strong>-t</strong> option says to use the
 513 headers to decide who to send the message to, and <strong>-odq</strong> says to put
 514 the message into the queue.  This last option means your message won't
 515 be immediately delivered, so leave it out if you want immediate
 516 delivery.</p>
 517 <p>Alternate, less convenient approaches include calling mail (sometimes
 518 called mailx) directly or simply opening up port 25 have having an
 519 intimate conversation between just you and the remote SMTP daemon,
 520 probably sendmail.</p>
 521 <p>Or you might be able use the CPAN module Mail::Mailer:</p>
 522 <pre>
 523     use Mail::Mailer;</pre>
 524 <pre>
 525     $mailer = Mail::Mailer-&gt;new();
 526     $mailer-&gt;open({ From    =&gt; $from_address,
 527                     To      =&gt; $to_address,
 528                     Subject =&gt; $subject,
 529                   })
 530         or die &quot;Can't open: $!\n&quot;;
 531     print $mailer $body;
 532     $mailer-&gt;close();</pre>
 533 <p>The Mail::Internet module uses Net::SMTP which is less Unix-centric than
 534 Mail::Mailer, but less reliable.  Avoid raw SMTP commands.  There
 535 are many reasons to use a mail transport agent like sendmail.  These
 536 include queuing, MX records, and security.</p>
 537 <p>
 538 </p>
 539 <h2><a name="how_do_i_use_mime_to_make_an_attachment_to_a_mail_message">How do I use MIME to make an attachment to a mail message?</a></h2>
 540 <p>This answer is extracted directly from the MIME::Lite documentation.
 541 Create a multipart message (i.e., one with attachments).</p>
 542 <pre>
 543     use MIME::Lite;</pre>
 544 <pre>
 545     ### Create a new multipart message:
 546     $msg = MIME::Lite-&gt;new(
 547                  From    =&gt;'me@myhost.com',
 548                  To      =&gt;'you@yourhost.com',
 549                  Cc      =&gt;'some@other.com, some@more.com',
 550                  Subject =&gt;'A message with 2 parts...',
 551                  Type    =&gt;'multipart/mixed'
 552                  );</pre>
 553 <pre>
 554     ### Add parts (each &quot;attach&quot; has same arguments as &quot;new&quot;):
 555     $msg-&gt;attach(Type     =&gt;'TEXT',
 556                  Data     =&gt;&quot;Here's the GIF file you wanted&quot;
 557                  );
 558     $msg-&gt;attach(Type     =&gt;'image/gif',
 559                  Path     =&gt;'aaa000123.gif',
 560                  Filename =&gt;'logo.gif'
 561                  );</pre>
 562 <pre>
 563     $text = $msg-&gt;as_string;</pre>
 564 <p>MIME::Lite also includes a method for sending these things.</p>
 565 <pre>
 566     $msg-&gt;send;</pre>
 567 <p>This defaults to using <em>sendmail</em> but can be customized to use
 568 SMTP via <a href="file://C|\msysgit\mingw\html/lib/Net/SMTP.html">the Net::SMTP manpage</a>.</p>
 569 <p>
 570 </p>
 571 <h2><a name="how_do_i_read_mail">How do I read mail?</a></h2>
 572 <p>While you could use the Mail::Folder module from CPAN (part of the
 573 MailFolder package) or the Mail::Internet module from CPAN (part
 574 of the MailTools package), often a module is overkill.  Here's a
 575 mail sorter.</p>
 576 <pre>
 577     #!/usr/bin/perl</pre>
 578 <pre>
 579     my(@msgs, @sub);
 580     my $msgno = -1;
 581     $/ = '';                    # paragraph reads
 582     while (&lt;&gt;) {
 583         if (/^From /m) {
 584             /^Subject:\s*(?:Re:\s*)*(.*)/mi;
 585             $sub[++$msgno] = lc($1) || '';
 586         }
 587         $msgs[$msgno] .= $_;
 588     }
 589     for my $i (sort { $sub[$a] cmp $sub[$b] || $a &lt;=&gt; $b } (0 .. $#msgs)) {
 590         print $msgs[$i];
 591     }</pre>
 592 <p>Or more succinctly,</p>
 593 <pre>
 594     #!/usr/bin/perl -n00
 595     # bysub2 - awkish sort-by-subject
 596     BEGIN { $msgno = -1 }
 597     $sub[++$msgno] = (/^Subject:\s*(?:Re:\s*)*(.*)/mi)[0] if /^From/m;
 598     $msg[$msgno] .= $_;
 599     END { print @msg[ sort { $sub[$a] cmp $sub[$b] || $a &lt;=&gt; $b } (0 .. $#msg) ] }</pre>
 600 <p>
 601 </p>
 602 <h2><a name="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_">How do I find out my hostname, domainname, or IP address?
 603 </a></h2>
 604 <p>(contributed by brian d foy)</p>
 605 <p>The Net::Domain module, which is part of the standard distribution starting
 606 in perl5.7.3, can get you the fully qualified domain name (FQDN), the host
 607 name, or the domain name.</p>
 608 <pre>
 609         use Net::Domain qw(hostname hostfqdn hostdomain);</pre>
 610 <pre>
 611         my $host = hostfqdn();</pre>
 612 <p>The <code>Sys::Hostname</code> module, included in the standard distribution since
 613 perl5.6, can also get the hostname.</p>
 614 <pre>
 615         use Sys::Hostname;</pre>
 616 <pre>
 617         $host = hostname();</pre>
 618 <p>To get the IP address, you can use the <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_gethostbyname"><code>gethostbyname</code></a> built-in function
 619 to turn the name into a number. To turn that number into the dotted octet
 620 form (a.b.c.d) that most people expect, use the <code>inet_ntoa</code> function
 621 from the &lt;Socket&gt; module, which also comes with perl.</p>
 622 <pre>
 623     use Socket;</pre>
 624 <pre>
 625     my $address = inet_ntoa(
 626         scalar gethostbyname( $host || 'localhost' )
 627         );</pre>
 628 <p>
 629 </p>
 630 <h2><a name="how_do_i_fetch_a_news_article_or_the_active_newsgroups">How do I fetch a news article or the active newsgroups?</a></h2>
 631 <p>Use the Net::NNTP or News::NNTPClient modules, both available from CPAN.
 632 This can make tasks like fetching the newsgroup list as simple as</p>
 633 <pre>
 634     perl -MNews::NNTPClient
 635       -e 'print News::NNTPClient-&gt;new-&gt;list(&quot;newsgroups&quot;)'</pre>
 636 <p>
 637 </p>
 638 <h2><a name="how_do_i_fetch_put_an_ftp_file">How do I fetch/put an FTP file?</a></h2>
 639 <p>LWP::Simple (available from CPAN) can fetch but not put.  Net::FTP (also
 640 available from CPAN) is more complex but can put as well as fetch.</p>
 641 <p>
 642 </p>
 643 <h2><a name="how_can_i_do_rpc_in_perl">How can I do RPC in Perl?</a></h2>
 644 <p>(Contributed by brian d foy)</p>
 645 <p>Use one of the RPC modules you can find on CPAN (
 646 <a href="http://search.cpan.org/search?query=RPC&mode=all">http://search.cpan.org/search?query=RPC&mode=all</a> ).</p>
 647 <p>
 648 </p>
 649 <hr />
 650 <h1><a name="author_and_copyright">AUTHOR AND COPYRIGHT</a></h1>
 651 <p>Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and
 652 other authors as noted. All rights reserved.</p>
 653 <p>This documentation is free; you can redistribute it and/or modify it
 654 under the same terms as Perl itself.</p>
 655 <p>Irrespective of its distribution, all code examples in this file
 656 are hereby placed into the public domain.  You are permitted and
 657 encouraged to use this code in your own programs for fun
 658 or for profit as you see fit.  A simple comment in the code giving
 659 credit would be courteous but is not required.</p>
 660 <table border="0" width="100%" cellspacing="0" cellpadding="3">
 661 <tr><td class="block" style="background-color: #cccccc" valign="middle">
 662 <big><strong><span class="block">&nbsp;perlfaq9 - Networking</span></strong></big>
 663 </td></tr>
 664 </table>
 665
 666 </body>
 667
 668 </html>