ch06_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

    { name     => "Martha",
      location => "Orlando",
      age      => "51" },
    { name     => "Betty",
      location => "Los Angeles",
      age      => "19" },
    ...
);</pre></blockquote>
</div>


<p><a href="ch06_03.htm#ch06-70025">Example 6-6</a> contains a script that will display all
of the standard colors available on systems that support the X Window
system.</p>

<a name="ch06-70025" /><div class="example">
<h4 class="objtitle">Example 6-6. xcolors.cgi</h4>

<blockquote><pre class="code">
#!/usr/bin/perl -wT

use strict;
use HTML::Template;

my $rgb_file = "/usr/X11/lib/X11/rgb.txt";
my $template = "/usr/local/apache/templates/xcolors.tmpl";

my @colors   = parse_colors( $rgb_file );

print "Content-type: text/html\n\n";
my $tmpl = new HTML::Template( filename =&gt; $template );

$tmpl-&gt;param( colors =&gt; \@colors );
print $tmpl-&gt;output;


sub parse_colors {
    my $path = shift;
    local *RGB_FILE;
    open RGB_FILE, $path or die "Cannot open $path: $!";
    
    while (&lt;RGB_FILE&gt;) {
        next if /^!/;
        chomp;
        my( $r, $g, $b, $name ) = split;
        
        # Convert to hexadecimal #RRGGBB format
        my $rgb = sprintf "#%0.2x%0.2x%0.2x", $r, $g, $b;
        
        my %color = ( rgb =&gt; $rgb, name =&gt; $name );
        push @colors, \%color;
    }
    
    close RGB_FILE;
    return @colors;
}</pre></blockquote>
</div>

<p>This CGI script uses the <tt class="function">rgb.txt</tt> file that is
typically found on X Window systems at
<em class="filename">/usr/X11/lib/X11/rgb.txt</em>. This file contains a
list of colors along with their 8-bit values for red, green, and
blue:</p>


<blockquote><pre class="code">! $XConsortium: rgb.txt,v 10.41 94/02/20 18:39:36 rws Exp $
255 250 250	    snow
248 248 255	    ghost white
248 248 255	    GhostWhite
245 245 245	    white smoke
245 245 245	    WhiteSmoke
...</pre></blockquote>


<p>We read the red, green, and blue values and convert them to the
hexadecimal equivalent that is used on HTML pages (e.g.,
<tt class="literal">#336699</tt>). We create a separate hash for each color
with an entry for the RGB value and the name of the color. Then we
add each hash to the array <tt class="literal">@colors</tt>. We need to
pass only <tt class="literal">@colors</tt> as a parameter to
HTML::Template, which we can use as a loop variable within our HTML
template. Within the loop, we have access to the "rgb"
and "name" elements of our hashes, as shown in <a href="ch06_03.htm#ch06-70010">Example 6-7</a>.</p>


<a name="ch06-70010" /><div class="example">
<h4 class="objtitle">Example 6-7. xcolors.tmpl</h4>

<blockquote><pre class="code">&lt;HTML&gt;

&lt;HEAD&gt;
  &lt;TITLE&gt;X11 Color Viewer&lt;/TITLE&gt;
&lt;/HEAD&gt;

&lt;BODY BGCOLOR="white"&gt;
&lt;DIV ALIGN="center"&gt;
  &lt;H1&gt;X11 Color Viewer&lt;/H1&gt;
  &lt;HR&gt;
  
  &lt;TABLE BORDER="1" CELLPADDING="4" WIDTH="400"&gt;
    &lt;TMPL_LOOP NAME="colors"&gt;
      &lt;TR&gt;
        &lt;TD BGCOLOR="&lt;TMPL_VAR NAME="rgb"&gt;"&gt;
          &amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&lt;/TD&gt;
        &lt;TD&gt;&lt;TMPL_VAR NAME="name"&gt;&lt;/TD&gt;
      &lt;/TR&gt;
    &lt;/TMPL_LOOP&gt;
  &lt;/TABLE&gt;
&lt;/DIV&gt;
&lt;/BODY&gt;
&lt;/HTML&gt;</pre></blockquote>
</div>

<p>This loop structure is flexible enough to allow us to display other
forms of data, such as hashes. <a href="ch06_03.htm#ch06-58970">Example 6-8</a> lists a
CGI script that generates all of the environment variables and their
values.</p>



<a name="ch06-58970" /><div class="example">
<h4 class="objtitle">Example 6-8. env_tmpl.cgi </h4>
<a name="INDEX-1378" /><a name="INDEX-1,379" />

<blockquote><pre class="code">#!/usr/bin/perl -wT

use strict;
use HTML::Template;

use constant TMPL_FILE =&gt; "$ENV{DOCUMENT_ROOT}/templates/env.tmpl";

my $tmpl = new HTML::Template( filename =&gt; TMPL_FILE,
                               no_includes =&gt; 1 );
my @env;

foreach ( sort keys %ENV ) {
    push @env, { var_name =&gt; $_, var_value =&gt; $ENV{$_} };
}

$tmpl-&gt;param( env =&gt; \@env );

print "Content-type: text/html\n\n",
      $tmpl-&gt;output;</pre></blockquote>
</div>


<p>HTML::Template has no facility for handling
<a name="INDEX-1380" />hashes directly, but because it will loop
over <a name="INDEX-1381" />arrays of
hashes, we build a hash for each pair in <tt class="literal">%ENV</tt> and
add it to an array, <tt class="literal">@env</tt>. We then pass a reference
to <tt class="literal">@env</tt> as a parameter to our HTML::Template
object and output the parsed file. Our template file is shown in
<a href="ch06_03.htm#ch06-54470">Example 6-9</a>.</p>



<a name="ch06-54470" /><div class="example">
<h4 class="objtitle">Example 6-9. env.tmpl </h4>
<a name="INDEX-1382" /><a name="INDEX-1,383" />

<blockquote><pre class="code">&lt;HTML&gt;

&lt;HEAD&gt;
  &lt;TITLE&gt;Environment Variables&lt;/TITLE&gt;
&lt;/HEAD&gt;

&lt;BODY BGCOLOR="white"&gt;
  &lt;TABLE BORDER="1"&gt;
    &lt;TMPL_LOOP NAME="env"&gt;
      &lt;TR&gt;
        &lt;TD&gt;&lt;B&gt;&lt;TMPL_VAR NAME="var_name"&gt;&lt;/B&gt;&lt;/TD&gt;
        &lt;TD&gt;&lt;TMPL_VAR NAME="var_value"&gt;&lt;/TD&gt;
      &lt;/TR&gt;
    &lt;/TMPL_LOOP&gt;
  &lt;/TABLE&gt;

&lt;/BODY&gt;
&lt;/HTML&gt;</pre></blockquote>
</div>


<p>Note that we called <tt class="function">param</tt> once, even though
there are three different HTML::Template tags in this file. The
<tt class="literal">var_name</tt> and <tt class="literal">var_value</tt>
variables were set because they corresponded to hash keys within the
<tt class="literal">@env</tt> array.</p>
</div>



<a name="ch06-7-fm2xml" /><div class="sect3">
<h3 class="sect3">6.3.1.2. Conditionals</h3>


<p>
<a name="INDEX-1384" /> <a name="INDEX-1,385" />HTML::Template
offers two ways to create a conditional just like Perl: TMPL_IF and
TMPL_UNLESS. You can use these to include or omit particular portions
of your HTML template. Both tags take a <a name="INDEX-1386" />
<a name="INDEX-1387" />NAME
attribute that corresponds to a parameter, just like previous tags,
which is evaluated in a boolean context. There is no way to create
expressions to evaluate within your templates, since the goal is to
keep templates simple. Note also that you do not always have to set a
separate parameter in order to use these tags. For example, you could
include a block like this in your document:</p>


<blockquote><pre class="code">&lt;TMPL_IF NAME="secret_msg" &gt;
  &lt;P&gt;Psst, here's your secret message: &lt;TMPL_VAR NAME="secret_msg"&gt;.&lt;/P&gt;
&lt;/TMPL_IF&gt;</pre></blockquote>


<p>Here the same parameter is used in both the TMPL_IF and TMPL_VAR
commands. If there is a secret message, it is displayed. If there
isn't (i.e., if it is an empty string), then nothing is
displayed instead.</p>


<p>You can also use
<a name="INDEX-1388" />
<a name="INDEX-1389" />loop parameters as conditions. If
the loop parameter contains any values, it returns true; otherwise it
returns false. This is useful for displaying search results when
there are no matches:</p>


<blockquote><pre class="code">&lt;P&gt;Here are the results of your query:&lt;/P&gt;

&lt;TABLE&gt;
  &lt;TR&gt;
    &lt;TH&gt;Software Title&lt;/TH&gt;&lt;/TR&gt;
    &lt;TH&gt;Home Page&lt;/TH&gt;&lt;/TR&gt;
  &lt;/TR&gt;
 
 &lt;TMPL_LOOP NAME="results"&gt;
  &lt;TR&gt;
    &lt;TD&gt;&lt;TMPL_VAR NAME="sw_title"&gt;&lt;/TD&gt;
    &lt;TD&gt;&lt;A HREF="&lt;TMPL_VAR NAME="url"&gt;"&gt;&lt;TMPL_VAR NAME="sw_url"&gt;&lt;/A&gt;&lt;/TD&gt;
  &lt;/TR&gt;
 &lt;/TMPL_LOOP&gt;
 
 &lt;TMPL_UNLESS NAME="results"&gt;
  &lt;TR&gt;
    &lt;TD COLSPAN="2"&gt;
      No software titles match your query.
    &lt;/TD&gt;
  &lt;/TR&gt;
 &lt;/TMPL_UNLESS&gt;

&lt;/TABLE&gt;</pre></blockquote>


<p>In this example, a user is searching for software according to some
criteria. If the query matches any titles, then the name and home
page of the titles are displayed on separate rows in a table. If no
rows match, then the script says this instead. This template gives
the interface designer full control over how the results are
presented to the user without being too complicated to understand.</p>
</div>



<a name="ch06-8-fm2xml" /><div class="sect3">
<h3 class="sect3">6.3.1.3. Including other files</h3>


<p>The final command,
<a name="INDEX-1390" />TMPL_INCLUDE, includes
the content of other files in your template. The content of these
files is included before loops and variables are parsed, so you can
include files that contain loop and variable tags (or even other
include tags). This is similar to the SSI
<tt class="command">include</tt>
<a name="INDEX-1391" /> command, except there is no ability to
provide a virtual
<a name="INDEX-1392" />path to the
file; you must provide a filesystem path. HTML::Template does no
validation that the file is within the document root, so an HTML
developer could easily include the following statement in a file and
HTML::Template would act accordingly:</p>


<blockquote><pre class="code">&lt;TMPL_INCLUDE NAME="/etc/passwd" &gt;</pre></blockquote>


<p>This is not as serious a security issue as it might appear, since an
HTML designer could always copy the contents of
<em class="emphasis">/etc/passwd</em> into an HTML file manually or create
a symbolic link to it. However, this potential is something you
should be aware of. You can disable includes entirely with the
<tt class="literal">no_includes</tt> option when you create an
HTML::Template object.</p>
</div>
</div>




<a name="ch06-9-fm2xml" /><div class="sect2">
<h3 class="sect2">6.3.2. Summary</h3>


<p>HTML::Template is certainly a very elegant solution for projects
where the roles of HTML designers and developers are clearly
separated. HTML::Template has only been available a short while but
has matured quickly. It also offers more advanced features including
caching output that we haven't discussed. The features we
discussed are accurate as of Version 1.7, but new features are still
being added, so check the documentation for more information. You can
find <a name="INDEX-1393" /> <a name="INDEX-1,394" />HTML::Template on CPAN; for the
latest information, including information on the mailing list and
CVS, consult the online <a name="INDEX-1395" /> <a name="INDEX-1,396" /> <a name="INDEX-1,397" /> <a name="INDEX-1,398" />documentation.</p>
</div>


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