Basic "Custom Tags" Parsing Script

Today we are going to create a basic Custom Tags parsing script that will parse
special symbols (tags) in text for formatting purpose. Just like writing <b>BOLD</b>,
a web browser parses it as “BOLD” in bold letters, same way our
script will parse tags created by us. One very popular example of custom tag
parsing for formatting purpose is, BBCode which most of the bulletin boards
use to let users format their posts.

This will be a basic example of parsing custom tags so we will only be parsing
two tags. One will convert the enclosing text into bold and other will be used
for italics. After understanding the basic idea, you can easily add more tags
according to your needs and can also use it wherever necessary. One of its good
use will be in Shout Boxes that we had designed a few months back.

Though many would like the use of Regular
Expressions for parsing, we will not be using them here. For the sake
of simplicity, we will be using only the basic string manipulation functions
available in PHP.

If you look at the code below, you can see an array (2D) holding our custom
tags. Here we’ll be having four information for each tag. Start tag, end
tag (both defined by us), HTML start tag and HTML end tag. To make this more
clear, let’s suppose we want to parse the text “[b]Text[/b]”
so that it’s displayed as “Text” in bold. Our start (custom)
tag will be [b], end tag will be [/b], HTML start
tag will be <b> and HTML end tag will be </b>.

As we will be parsing two different custom tags, we have eight elements in
the array. If you want to add more tags, add four elements for each tag, just
like the way the others are. No need to change anything else.

The code:


<form name="form1" method="get" action="">

  <p>

    <!-- textarea should display previously wriiten text -->


    <textarea name="content" cols="35" rows="12" id="content"><? 
if (isset($_GET['content'])) echo $_GET['content']; ?></textarea>


  </p>

  <p>

    <input name="parse" type="submit" id="parse" value="Parse">

  </p>

</form>

<?



if(isset($_GET['parse']))


{

    $content = $_GET['content'];

    //convert newlines in the text to HTML "<br />"


    //required to keep formatting (newlines)

    $content = nl2br($content);

    

    /* CUSTOM TAGS

    -----------

    */




    //For Tag 1

    $tag[0][0] = '[b]';

    $tag[0][1] = '[/b]';


    $tag[0][2] = '<strong>';

    $tag[0][3] = '</strong>';




    //For Tag 2    

    $tag[1][0] = '[i]';

    $tag[1][1] = '[/i]';


    $tag[1][2] = '<i>';

    $tag[1][3] = '</i>';




    //count total no. of tags to parse

    $total_tags = count($tag); //2 for now


    

    //parse our custom tags adding HTML tags instead

    //which a browser can understand

    for($i = 0; $i<$total_tags; $i++)


    {    

        $content = str_replace($tag[$i][0],$tag[$i][2],$content);


        $content = str_replace($tag[$i][1],$tag[$i][3],$content);


    }

    

    //now the variable $content contains HTML formatted text

    //display it

    echo '<hr />';


    echo $content;

}

?>