Regular expression help

Hi,
can someone help me to write the right regular expression for the following.

Let we have the folowing text sourse

This is example text with keyword and 
also <a href="http://www.somekeyword.com">linking page</a> and so on..

Code (markup):

I want the keyword "keyword" to be replaced with "<b>keyword</b>"

We I use the following:

$text = // the text source above
$text = preg_replace('/keyword/i', '<b>\\0</b>', $text);

PHP:

it returns

This is example text with <b>keyword</b> and 
also <a href="http://www.some<b>keyword</b>.com">linking page</a> and so on..

Code (markup):

I want the "keyword" in the url NOT to be replaced.

Any advice how can do this?

 

Please Use This this may work according to your requirement.

<?php
$text = 'This is example text with keyword and also <a href="http://www.somekeyword.com">linking page</a> and so on..';// the text source above
$text = preg_replace('/ keyword /i', '<b>\\0</b>', $text);
echo $text;
?>

 

@shivakhanal thanks but your solution not helps me if we have for example 'somekeywod' not in the URL

 

please try this

<?
$text = // the text source above
$text = preg_replace("#(^[<a])+(.+?)keyword#si"', '<b>\\0</b>', $text);
?>

PHP:

i dont try code but i think it will work
explain is:
^[<a] = not start with <a