ch05_03.htm

用perl编写CGI的好书。本书从解释CGI和底层HTTP协议如何工作开始

<p>This usage makes it easy to nest elements:</p>


<blockquote><pre class="code">print $q-&gt;p( "The server name is:", $q-&gt;em( $q-&gt;server_name ) );</pre></blockquote>




<p>This prints the text:</p>


<blockquote><pre class="code">&lt;P&gt;The server name is: &lt;EM&gt;localhost&lt;/EM&gt;&lt;/P&gt;</pre></blockquote>



<p>Note that a space is automatically added between each
<a name="INDEX-1148" />
<a name="INDEX-1149" />list element. It appears after the colon
in these examples. If you wish to print multiple items in a list
without intervening
<a name="INDEX-1150" />spaces, then you
must set Perl's list separator variable, <tt class="literal">$"</tt>,
to an empty string:</p>


<blockquote><pre class="code">{ 
  local $" = "";
  print $q-&gt;p( "Server=", $q-&gt;server_name );
}</pre></blockquote>




<p>This prints the text:</p>



<blockquote><pre class="code">&lt;P&gt;Server=Apache/1.3.9&lt;/P&gt;</pre></blockquote>



<p>Note that whenever you change global variables like
<tt class="literal">$"</tt>, you should localize them by enclosing them in
blocks and using <a name="INDEX-1151" /> <a name="INDEX-1,152" />Perl's
<tt class="function">local</tt> function.</p></li>

<li><p>If the first argument is a reference to a hash, then the
<a name="INDEX-1153" />hash elements
are interpreted as
<a name="INDEX-1154" />attributes for
the HTML element:</p>


<blockquote><pre class="code">print $q-&gt;a( { -href =&gt; "/downloads" }, "Download Area" );</pre></blockquote>




<p>This prints the text:</p>



<blockquote><pre class="code">&lt;A HREF="/downloads" &gt;Download Area&lt;/A&gt;</pre></blockquote>



<p>You can specify as many attributes as you want. The leading
<a name="INDEX-1155" />hyphen as part of the attribute name is
not required, but it is the standard convention.</p>


<p>Some
attributes do not take arguments and simply appear as a word. For
these, pass <tt class="literal">undef</tt> as the value of the attribute.
Prior to version 2.41 of CGI.pm, passing an empty string would
accomplish the same thing, but that was changed so that people could
explicitly request an attribute set to an empty string (e.g., &lt;IMG
HREF="spacer.gif" ALT=""&gt;).</p></li>

<li><p>If
you provide a reference to an
<a name="INDEX-1156" />array as an argument, the tag is
distributed across each item in the array:</p>



<blockquote><pre class="code">print $q-&gt;ol( $q-&gt;li( [ "First", "Second", "Third" ] ) );</pre></blockquote>




<p>This corresponds to:</p>



<blockquote><pre class="code">&lt;OL&gt;
  &lt;LI&gt;First&lt;/LI&gt;
  &lt;LI&gt;Second&lt;/LI&gt;
  &lt;LI&gt;Third&lt;/LI&gt;
&lt;/OL&gt;</pre></blockquote>



<p>This still works fine when the first argument is a reference to
a hash arguments. Here is a table:</p>


<blockquote><pre class="code">print $q-&gt;table(
                 { -border =&gt; 1,
                   -width  =&gt; "100%" },
                 $q-&gt;Tr( [
                           $q-&gt;th( { -bgcolor =&gt; "#cccccc" },
                                   [ "Name", "Age" ] ),
                           $q-&gt;td( [ "Mary", 29 ] ),
                           $q-&gt;td( [ "Bill", 27 ] ),
                           $q-&gt;td( [ "Sue",  26 ] )
                       ] )
               );</pre></blockquote>




<p>This corresponds to:</p>



<blockquote><pre class="code">&lt;TABLE BORDER="1" WIDTH="100%"&gt;
  &lt;TR&gt;
    &lt;TH BGCOLOR="#cccccc"&gt;Name&lt;/TH&gt;
    &lt;TH BGCOLOR="#cccccc"&gt;Age&lt;/TH&gt;
  &lt;/TR&gt;
  &lt;TR&gt;
    &lt;TD&gt;Mary&lt;/TD&gt;
    &lt;TD&gt;29&lt;/TD&gt;
  &lt;/TR&gt;
  &lt;TR&gt;
    &lt;TD&gt;Bill&lt;/TD&gt;
    &lt;TD&gt;27&lt;/TD&gt;
  &lt;/TR&gt;
  &lt;TR&gt;
    &lt;TD&gt;Sue&lt;/TD&gt;
    &lt;TD&gt;26&lt;/TD&gt;
  &lt;/TR&gt;
&lt;/TABLE&gt;</pre></blockquote></li>

<li><p>Aside from the <a name="INDEX-1157" />spaces we mentioned above that are
introduced between array elements, CGI.pm does not insert any
whitespace between HTML elements. It creates no indentation and
inserts no new lines. Although this makes it harder for a human to
read, it also makes the output smaller and downloads faster. If you
wish to generate neatly formatted HTML code, you can use the
<a name="INDEX-1158" />
<a name="INDEX-1159" />CGI::Pretty module distributed with
CGI.pm. It provides all of the features of CGI.pm (because it is an
object-oriented module that extends CGI.pm), but the HTML it produces
is <a name="INDEX-1160" />neatly
indented.</p></li></ul>
</div>




<a name="ch05-24-fm2xml" /><div class="sect2">
<h3 class="sect2">5.3.4. Form Elements</h3>


<p>The syntax for generating
<a name="INDEX-1161" />
<a name="INDEX-1162" />form elements differs from other
elements. These methods only take name-value pairs that correspond to
the attributes. See <a href="ch05_03.htm#ch05-22489">Table 5-2</a>.</p>



<a name="ch05-22489" /><h4 class="objtitle">Table 5-2. CGI.pm Methods for HTML Form Elements </h4><table border="1">



<tr>
<th>
<p>CGI.pm Method</p></th>
<th>
<p>HTML Tag</p></th>
</tr>




<tr>
<td>
<p><em class="emphasis">start_form</em></p></td>
<td>
<p>&lt;FORM&gt;</p></td>
</tr>

<tr>
<td>
<p><em class="emphasis">end_form</em></p></td>
<td>
<p>&lt;/FORM&gt;</p></td>
</tr>

<tr>
<td>
<p><em class="emphasis">textfield</em></p></td>
<td>
<p>&lt;INPUT TYPE="TEXT" &gt;</p></td>
</tr>

<tr>
<td>
<p><em class="emphasis">password_field</em></p></td>
<td>
<p>&lt;INPUT TYPE="PASSWORD" &gt;</p></td>
</tr>

<tr>
<td>
<p><em class="emphasis">filefield</em></p></td>
<td>
<p>&lt;INPUT TYPE="FILE" &gt;</p></td>
</tr>

<tr>
<td>
<p><em class="emphasis">button</em></p></td>
<td>
<p>&lt;INPUT TYPE="BUTTON" &gt;</p></td>
</tr>

<tr>
<td>
<p><em class="emphasis">submit</em></p></td>
<td>
<p>&lt;INPUT TYPE="SUBMIT" &gt;</p></td>
</tr>

<tr>
<td>
<p><em class="emphasis">reset</em></p></td>
<td>
<p>&lt;INPUT TYPE="RESET" &gt;</p></td>
</tr>

<tr>
<td>
<p><em class="emphasis">checkbox, checkbox_group</em></p></td>
<td>
<p>&lt;INPUT TYPE="CHECKBOX" &gt;</p></td>
</tr>

<tr>
<td>
<p><em class="emphasis">radio_group</em></p></td>
<td>
<p>&lt;INPUT TYPE="RADIO" &gt;</p></td>
</tr>

<tr>
<td>
<p><em class="emphasis">popup_menu</em></p></td>
<td>
<p>&lt;SELECT SIZE="1" &gt;</p></td>
</tr>

<tr>
<td>
<p><em class="emphasis">scrolling_list</em></p></td>
<td>
<p>&lt;SELECT SIZE="n" &gt; where n &gt; 1</p></td>
</tr>

<tr>
<td>
<p><em class="emphasis">textarea</em></p></td>
<td>
<p>&lt;TEXTAREA&gt;</p></td>
</tr>

<tr>
<td>
<p><em class="emphasis">hidden</em></p></td>
<td>
<p>&lt;INPUT TYPE="HIDDEN" &gt;</p></td>
</tr>


</table>


<p>The <tt class="function">start_form</tt> and <tt class="function">end_form</tt>
elements generate the opening and closing form tags.
<tt class="function">start_form</tt> takes arguments for each of its
attributes:</p>


<blockquote><pre class="code">print $q-&gt;start_form( method =&gt; "get", action =&gt; "/cgi/myscript.cgi" );</pre></blockquote>


<p>Note that unlike a typical form tag, CGI.pm sets the request method
to POST instead of GET by default (the reverse of the default for
HTML forms). If you want to allow file uploads, use the
<tt class="function">start_multipart_form</tt> method instead of
<tt class="function">start_form</tt>, which sets <em class="emphasis">enctype</em> to
"multipart/form-data".</p>


<p>All of the remaining methods create form elements. They all take the
<tt class="literal">-name</tt> and <tt class="literal">-default</tt> arguments.
The <tt class="literal">-default</tt> value for an element is replaced by
the corresponding value from <tt class="function">param</tt> if that value
exists. You can disable this and force the default to override a
user's parameters by passing the <tt class="literal">-override</tt>
argument with a true value.</p>


<p>The <tt class="literal">-default</tt> option specifies the default
<em class="emphasis">value</em> of the element for elements with single
values:</p>


<blockquote><pre class="code">print $q-&gt;textfield(
        -name    =&gt; "username",
        -default =&gt; "Anonymous"
      );</pre></blockquote>


<p>This yields:</p>


<blockquote><pre class="code">&lt;INPUT TYPE="text" NAME="username" VALUE="Anonymous"&gt;</pre></blockquote>


<p>By supplying an array with the <tt class="literal">-values</tt> argument,
the <tt class="function">checkbox_group</tt> and
<tt class="function">radio_group</tt> methods generate multiple checkboxes
that share the same name. Likewise, passing an array reference with
the <tt class="literal">-values</tt> argument to the
<tt class="function">scrolling_list</tt> and
<tt class="function">popup_menu</tt> functions generates both the
&lt;SELECT&gt; and &lt;OPTION&gt; elements. For these elements,
<tt class="literal">-default</tt> indicates the values that are checked or
selected; you can pass <tt class="literal">-default</tt> a reference to an
array for <tt class="function">checkbox_group</tt> and
<tt class="function">scrolling_list</tt> for multiple defaults.</p>


<p>Each method accepts a <tt class="literal">-labels</tt> argument that takes
a reference to a hash; this hash associates the value of each element
to the label the browser displays to the user.</p>


<p>Here is how you can generate a group of radio buttons:</p>


<blockquote><pre class="code">print $q-&gt;radio_group(
        -name    =&gt; "curtain",
        -values  =&gt; [ "A", "B", "C" ],
        -default =&gt; "B",
        -labels  =&gt; { A =&gt; "Curtain A", B =&gt; "Curtain B", C =&gt; "Curtain C" }
      );</pre></blockquote>


<p>This yields:</p>


<blockquote><pre class="code">&lt;INPUT TYPE="radio" NAME="look_behind" VALUE="A"&gt;Curtain A
&lt;INPUT TYPE="radio" NAME="look_behind" VALUE="B" CHECKED&gt;Curtain B
&lt;INPUT TYPE="radio" NAME="look_behind" VALUE="C"&gt;Curtain C</pre></blockquote>


<p>For specifying any other attributes for form elements, like SIZE=4,
pass them as additional <a name="INDEX-1164" /> <a name="INDEX-1,165" />arguments (e.g., <tt class="literal">size =&gt;
4</tt>).</p>
</div>


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