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Basic "Custom Tags" Parsing Script

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="">
    <!-- textarea should display previously wriiten text -->
    <textarea name="content" cols="35" rows="12" id="content"><? 
if (isset(
$_GET['content'])) echo $_GET['content']; ?></textarea>
    <input name="parse" type="submit" id="parse" value="Parse">

$content $_GET['content'];
//convert newlines in the text to HTML "<br />"
    //required to keep formatting (newlines)
$content nl2br($content);

    //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 />';

The code is pretty straightforward. Isn’t it!

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