an example show you how to use php convert bbcode to html tags

bbcode2html.php

<?php
/**
 * bbcode2html
 *
 * @desc 用正则将帖子内容里面的UBBCODE转换为HTML标签显示
 * @see http://php.net/manual/en/function.bbcode-create.php
 * @param string $content
 * @param boolean $nl2br
 * @return string
 */
function bbcode2html($content, $nl2br = true)
{
    //匹配模式
    $pattern = array(
        "/\[b\](.*)\[\/b\]/is",
        "/\[u\](.*)\[\/u\]/is",
        "/\[i\](.*)\[\/i\]/is",
        "/\[quote\](.*)\[\/quote\]/is",
        "/\[color=([^\[\<]+?)\](.*)\[\/color\]/is",
        "/\[font=([^\[\<]+?)\](.*)\[\/font\]/is",
        "/\[size=(\d+?)\](.*)\[\/size\]/is",
        "/\[url\](.*)\[\/url\]/i",
        "/\[url=(.*)\](.*)\[\/url\]/i",
        "/\[flash=(\d+),(\d+)\]\s*([^\[\<\r\n]+?)\s*\[\/flash\]/i",
        "/\[swf\]\s*([^\[\<\r\n]+?)\s*\[\/swf\]/i",
        "/\[img\]\s*([^\[\<\r\n]+?)\s*\[\/img\]/i",
    );
    
    //替换格式
    $replacement = array(
        "<b>\\1</b>",
        "<u>\\1</u>",
        "<i>\\1</i>",
        "<blockquote>\\1</blockquote>",
        "<font color=\"\\1\">\\2</font>",
        "<font face=\"\\1\">\\2</font>",
        "<font size=\"\\1\">\\2</font>",
        "<a href=\"\\1\" target=\"_blank\">\\1</a>",
        "<a href=\"\\1\" target=\"_blank\">\\2</a>",
        "<p><embed width=\"\\1\" height=\"\\2\" src=\"\\3\"></embed></p>",
        "<p><embed width=\"500\" height=\"400\" src=\"\\1\"></embed></p>",
        "<a href=\"\\1\" target=\"_blank\"><img src=\"\\1\" alt=\"\\1\" border=\"0\" /></a>",
    );
    
    //针对$content字符串进行$pattern规则的正则匹配并替换为$replacement所定义的格式
    //可自行定义更多规则，保证一一对应就行了
    $content = preg_replace($pattern, $replacement, $content);
    
    //(不)换行, \n convert to <br />
    $content = $nl2br === true ? nl2br($content) : $content;
    
    return $content;
}

// try
$str = <<<EOF
[url=http://www.eoeandroid.com/faq.php?action=faq&id=5&messageid=18]http://www.eoeandroid.com/faq.php?action=faq&id=5&messageid=18[/url]
[url]http://www.eoeandroid.com/faq.php?action=faq&id=5&messageid=18[/url]
EOF;

echo bbcode2html($str);

// 另外一种方式可以参考 http://php.net/manual/en/function.bbcode-create.php
?>