ch20.htm

this is a book on pearl , simple example with explanation is given here. it could be beneficial for

Define the </I><TT><I>getFormData()</I></TT><I>

fuNCtion.<BR>

Declare a local variable to hold the refereNCe to the input field

hash.<BR>

Initialize a buffer.<BR>

If the </I><TT><I>GET</I></TT><I>

method is used, copy the form information into the buffer.<BR>

If the </I><TT><I>POST</I></TT><I>

method is used, read the form information into the buffer.<BR>

Iterate over the array returned by the </I><TT><I>split()</I></TT><I>

fuNCtion.<BR>

Decode both the input field name and value.<BR>

Compress multiple </I><TT><I>&lt;P&gt;</I></TT><I>

tags into one.<BR>

Convert </I><TT><I>&lt;</I></TT><I>

into </I><TT><I>&amp;lt;</I></TT><I>

and </I><TT><I>&gt;</I></TT><I> into

</I><TT><I>&amp;gt;</I></TT><I> stopping

HTML tags from interpretation.<BR>

Turn back on the bold and italic HTML tags.<BR>

Remove unneded carriage returns.<BR>

Convert two newlines into a HTML paragraph tag.<BR>

Convert single newlines into spaces.<BR>

Create an entry in the input field hash variable.<BR>

Define the </I><TT><I>decodeURL()</I></TT><I>

fuNCtion.<BR>

Get the eNCoded string from the parameter array.<BR>

Translate all plus signs into spaces.<BR>

Convert character coded as hexadecimal digits into regular characters.

<BR>

Return the decoded string.<BR>

Define the </I><TT><I>zeroFill()</I></TT><I>

fuNCtion-turns &quot;1&quot; into &quot;01&quot;.<BR>

Declare a local variable to hold the number to be filled.<BR>

Declare a local variable to hold the string length that is needed.

<BR>

Find differeNCe between current string length and needed length.

<BR>

If the string is big enough (like &quot;12&quot;) then return

it.<BR>

If the string is too big, prefix it with some zeroes.<BR>

Define the </I><TT><I>saveFormData()</I></TT><I>

fuNCtion.<BR>

Declare two local variables to hold the hash and file name.<BR>

Open the file for appending.<BR>

Store the contents of the hash in the data file.<BR>

Close the file.</I>

</BLOCKQUOTE>

<HR>

<BLOCKQUOTE>

<B>Listing 20.6&nbsp;&nbsp;20LST06.PL-A More AdvaNCed Guestbook

<BR>

</B>

</BLOCKQUOTE>

<BLOCKQUOTE>

<PRE>

#! /user/bin/perl -w

#use strict;



    my(%fields);

    my($sec, $min, $hour, $mday, $mon, $year) = (localtime(time))[0..5];

    my($dataFile) = &quot;data/gestbook.dat&quot;;



    $mon  = zeroFill($mon, 2);

    $hour = zeroFill($hour, 2);

    $min  = zeroFill($min, 2);

    $sec  = zeroFill($sec, 2);

    $fields{'timestamp'} = &quot;$mon/$mday/$year, $hour:$min:$sec&quot;;



    getFormData(\%fields);



    if ($ENV{'QUERY_STRING'}) {

        if ($ENV{'QUERY_STRING'} eq 'display') {

            displayPage();

        }

        elsif ($ENV{'QUERY_STRING'} eq 'add') {

            print(&quot;Location: /addgest.htm\n\n&quot;);

        }

        else {

            displayError(&quot;Unknown Command: &lt;B&gt;$ENV{'QUERY_STRING'}&lt;/B&gt;&quot;);

        }

    }

    else {

        if (length($fields{'name'}) == 0) {

            displayError(&quot;Please fill the name field,&lt;BR&gt;\n&quot;);

        }

if (length($fields{'comments'}) == 0) {

            displayError(&quot;Please fill the comments field,&lt;BR&gt;\n&quot;);

        }

        saveFormData(\%fields, $dataFile);

        displayPage();

    }



    exit(0);



sub displayError {

    print(&quot;Content-type: text/html\n\n&quot;);

    print(&quot;&lt;HTML&gt;\n&quot;);

    print(&quot;&lt;HEAD&gt;&lt;TITLE&gt;Guestbook Error&lt;/TITLE&gt;&lt;/HEAD&gt;\n&quot;);

    print(&quot;&lt;H1&gt;Guestbook&lt;/H1&gt;\n&quot;);

    print(&quot;&lt;HR&gt;\n&quot;);

    print(&quot;@_&lt;BR&gt;\n&quot;);

    print(&quot;&lt;HR&gt;\n&quot;);

    printENV();

    print(&quot;&lt;/BODY&gt;\n&quot;);

    print(&quot;&lt;/HTML&gt;\n&quot;);

    exit(0);

}



        

sub displayPage {

    my(%entries);



    readFormData($dataFile, \%entries);



    print(&quot;Content-type: text/html\n\n&quot;);

    print(&quot;&lt;HTML&gt;\n&quot;);

    print(&quot;&lt;HEAD&gt;&lt;TITLE&gt;Guestbook&lt;/TITLE&gt;&lt;/HEAD&gt;\n&quot;);

    print(&quot;&lt;TABLE&gt;&lt;TR&gt;&lt;TD VALIGN=top&gt;&lt;H1&gt;Guestbook&lt;/H1&gt;&lt;/TD&gt;\n&quot;);



    print(&quot;&lt;TD VALIGN=top&gt;&lt;UL&gt;&lt;LI&gt;&lt;A HREF=\&quot;/cgi-bin/gestbook.pl?add\&quot;&gt;Add an Entry&lt;/A&gt;\n&quot;);

    print(&quot;&lt;LI&gt;&lt;A HREF=\&quot;/cgi-bin/gestbook.pl?display\&quot;&gt;Refresh&lt;/A&gt;&lt;/UL&gt;&lt;/TD&gt;&lt;/TR&gt;&lt;/TABLE&gt;\n&quot;);

    print(&quot;&lt;HR&gt;\n&quot;);



    foreach (sort(keys(%entries))) {

        my($arrayRef) = $entries{$_};

        my($timestamp, $name, $email, $comments) = ($_, @{$arrayRef});



        print(&quot;$timestamp: &lt;B&gt;$name&lt;/B&gt; &lt;A HREF=mailto:$email&gt;$email&lt;/A&gt;\n&quot;);

        print(&quot;&lt;OL&gt;$comments&lt;/OL&gt;\n&quot;);

        print(&quot;&lt;HR&gt;\n&quot;);

    }

    print(&quot;&lt;/BODY&gt;\n&quot;);

    print(&quot;&lt;/HTML&gt;\n&quot;);

}



sub readFormData {

    my($file)    = shift;

    my($hashRef) = shift;



    open(FILE, &quot;&lt;$file&quot;) or displayError(&quot;Unable to open Guestbook data file.&quot;);

    while (&lt;FILE&gt;) {

        my($timestamp, $name, $email, $comments) = split(/~/, $_);



        $hashRef-&gt;{$timestamp} = [ $name, $email, $comments ];

    }

    close(FILE);

}



sub getFormData {

    my($hashRef) = shift;

    my($buffer) = &quot;&quot;;



    if ($ENV{'REQUEST_METHOD'} eq &quot;GET&quot;) {

        $buffer = $ENV{'QUERY_STRING'};

    }

    

   else {

        read(STDIN, $buffer, $ENV{'CONTENT_LENGTH'});

    }



    foreach (split(/&amp;/, $buffer)) {

        my($key, $value) = split(/=/, $_);

        $key   = decodeURL($key);

        $value = decodeURL($value);



        $value =~ s/(&lt;P&gt;\s*)+/&lt;P&gt;/g;   # compress multiple &lt;P&gt; tags.

        $value =~ s/&lt;/&amp;lt;/g;           # turn off all HTML tags.

        $value =~ s/&gt;/&amp;gt;/g;

        $value =~ s/&amp;lt;b&amp;gt;/&lt;b&gt;/ig;    # turn on the bold tag.

        $value =~ s!&amp;lt;/b&amp;gt;!&lt;/b&gt;!ig;

        $value =~ s/&amp;lt;i&amp;gt;/&lt;b&gt;/ig;    # turn on the italic tag.

        $value =~ s!&amp;lt;/i&amp;gt;!&lt;/b&gt;!ig;

        $value =~ s!\cM!!g;            # Remove unneeded carriage returns.

        $value =~ s!\n\n!&lt;P&gt;!g;        # Convert 2 newlines into paragraph.

        $value =~ s!\n! !g;            # convert newline into space.

        %{$hashRef}-&gt;{$key} = $value;

    }

}



sub decodeURL {

    $_ = shift;

    tr/+/ /;

    s/%(..)/pack('c', hex($1))/eg;

    return($_);

}



sub zeroFill {

    my($temp) = shift;

    my($len)  = shift;

    my($diff) = $len - length($temp);



    return($temp) if $diff &lt;= 0;

    return(('0' x $diff) . $temp);

}



sub saveFormData {

    my($hashRef) = shift;

    my($file)    = shift;



    open(FILE, &quot;&gt;&gt;$file&quot;) or die(&quot;Unable to open Guestbook data file.&quot;);

    print FILE (&quot;$hashRef-&gt;{'timestamp'}~&quot;);

    print FILE (&quot;$hashRef-&gt;{'name'}~&quot;);

    print FILE (&quot;$hashRef-&gt;{'email'}~&quot;);

    print FILE (&quot;$hashRef-&gt;{'comments'}&quot;);

    print FILE (&quot;\n&quot;);

    

close(FILE);

}



sub printENV {

    print &quot;The Environment report&lt;BR&gt;\n&quot;;

    print &quot;----------------------&lt;BR&gt;&lt;PRE&gt;\n&quot;;

    print &quot;REQUEST_METHOD:  *$ENV{'REQUEST_METHOD'}*\n&quot;;

    print &quot;SCRIPT_NAME:     *$ENV{'SCRIPT_NAME'}*\n&quot;;

    print &quot;QUERY_STRING:    *$ENV{'QUERY_STRING'}*\n&quot;;

    print &quot;PATH_INFO:       *$ENV{'PATH_INFO'}*\n&quot;;

    print &quot;PATH_TRANSLATED: *$ENV{'PATH_TRANSLATED'}*&lt;/PRE&gt;\n&quot;;



    if ($ENV{'REQUEST_METHOD'} eq 'POST') {

        print &quot;CONTENT_TYPE:    $ENV{'CONTENT_TYPE'}&lt;BR&gt;\n&quot;;

        print &quot;CONTENT_FILE:    $ENV{'CONTENT_FILE'}&lt;BR&gt;\n&quot;;

        print &quot;CONTENT_LENGTH:  $ENV{'CONTENT_LENGTH'}&lt;BR&gt;\n&quot;;

    }

    print(&quot;&lt;BR&gt;&quot;);



    foreach (sort(keys(%ENV))) {

        print(&quot;$_: $ENV{$_}&lt;BR&gt;\n&quot;);

    }

    print(&quot;&lt;BR&gt;&quot;);



     foreach (sort(keys(%fields))) {

        print(&quot;$_: $fields{$_}&lt;BR&gt;\n&quot;);

    }

    print(&quot;&lt;BR&gt;&quot;);

}

</PRE>

</BLOCKQUOTE>

<HR>

<P>

One of the major changes between Listing 20.5 and Listing 20.6

is in the <TT>readFormData()</TT>

fuNCtion. Instead of actually printing the Guest book data, the

fuNCtion now creates hash entries for it. This change was done

so that an error page could be generated if the data file could

not be opened. Otherwise, the error message would have appeared

it the middle of the Guest book page-leading to confusion on the

part of vistors.

<P>

A table was used to add two hypertext links to the top of the

web page. One link will let visitors add a new entry and the other

refreshes the page. If a second visitor has added a Guest book

entry while the first visitor was reading, refreshing the page

will display the new entry.

<H2><A NAME="Summary"><FONT SIZE=5 COLOR=#FF0000>

Summary</FONT></A></H2>

<P>

This chapter introduced you to HTML forms and form processing.

You learned that HTML tags are used to provide guidelines about

how the content of a document. For example, the <TT>&lt;P&gt;</TT>

tag indicates a new paragraph is starting and the <TT>&lt;H1&gt;..&lt;/H1&gt;</TT>

tags indicate a text heading.

<P>

A &quot;correct&quot; HTML document will be entirely eNClosed

inside of a set of &lt;HTML&gt;..&lt;/HTML&gt; tags. Inside the

<TT>&lt;HTML&gt;</TT> tag are <TT>&lt;HEAD&gt;..&lt;/HEAD&gt;</TT>

(surrounds document identification information) and <TT>&lt;BODY&gt;..&lt;/BODY&gt;</TT>

(surrounds document content information) tags.

<P>

After the brief introduction to HTML, you read about Server-Side

INCludes. They are used to insert information into a document

at the time that the page is sent to the Web browser. This lets

the document designer create dynamic pages without needing CGI

programs. For example, you can display the last modification date

of a document, or iNClude other document such as a standard footer

file.

<P>

Next, HTML forms were discussed. HTML forms display input fields

that query the visitor to your Web site. You can display input

boxes, checkboxes, radio but-tons, selection lists, submit buttons

and reset buttons. Everything inside a set of <TT>&lt;FORM&gt;..&lt;/FORM&gt;</TT>

tags is considered one form. You can have multiple forms on a

single Web page.

<P>

The <TT>&lt;FORM&gt;</TT> tag takes

two modifiers. The <TT>ACTION</TT>

modifier tell the web browser the name of the CGI program that

gets invoked when the form's submit button is clicked. And the

<TT>METHOD</TT> modifier determines

how the form information should be sent to the CGI program. If

the <TT>GET</TT> method is used, the

information from the form's fields will be available in the <TT>QUERY_STRING</TT>

environment variable. IF the <TT>POST</TT>

method is used, the form information will be available via the

<TT>STDIN</TT> variable.

<P>

The <TT>getFormData()</TT> fuNCtion

was developed to process form information about make it available

via a hash variable. This fuNCtion is the first line of defense

against hackers. By investing time developing this fuNCtion to

close security holes, you are rewarded by having a safer, more

stable web site.

<P>

Debugging a CGI script takes a little bit of preparation. First,

create a batch or shell file that defines the environment variables

that your CGI program needs. Then, create a test input file if

you are using the <TT>POST</TT> method.

Lastly, execute the CGI program from the command line using redirection

to point STDIN to your test input file.

<P>

Next, a Guestbook application was presented. This application

used an HTML form to gather comments from a user. The comments

are saved to a database. Then, all of the comments stored in the

database are displayed. The first version of the Guestbook required

the user to add an entry before seeing the contents of the Guest-

book. The second version of the Guestbook let users view the contents

without this requirement. In addition, better error checking and

new features were added.

<P>

The next chapter, &quot;Using Perl with Web Servers,&quot; explores

web server log files and ways to automatically create Web pages.

<H2><A NAME="ReviewQuestions"><FONT SIZE=5 COLOR=#FF0000>

Review Questions</FONT></A></H2>

<P>

Answers to Review Questions are in Appendix A. 

<OL>

<LI>What does the acronym HTML stand for?

<LI>What are the &lt;H1&gt;..&lt;/H1&gt; set of tags used for?

<LI>What is the down side of using SSI directives?

<LI>Can an HTML form have two submit buttons?

<LI>Why should all angle brackets be replaced in form information?

<LI>How much text can be entered into a &lt;TEXTAREA&gt; input

field?

<LI>Can you debug a CGI script?

</OL>

<H2><A NAME="ReviewExercises"><FONT SIZE=5