For converting plain text to html

gistfile1.php

<?php

/**
Basically is used to convert plain text to html.
@author Nat Welch
*/

function htmlify($str)
{
    // replace special characters with HTML entities
    $html = htmlspecialchars($str);
    
    //paragraph-ise
    $html = "<p>" . str_replace("\n\n", "</p>\n<p>", $html) . "</p>";

    // replace multiple spaces with single spaces
    $html = preg_replace('/\s\s+/', ' ', $html);

    // replace URLs with <a href...> elements
    $html = preg_replace('/\s(\w+:\/\/)(\S+)/', ' <a href="\\1\\2" title="\\2">\\1\\2</a>', $html);
    
    return $html;
}

?>