Problems with search feature on homemade forum

[Adamthenewbie]

I recently built a search function into my homemade forum. Everything works great except for one little problem.

When the user clicks on a Topic that was returned from his/her search the words they searched for get highlighted. It worked great except for one small issue. Lets say a user searched for the keyword "Hi"

With the code I am currently using (attached below) it highlights everywhere in the message there is the text Hi, but my problem is it messes up different codes like for example: [ IMG=http://google.com/images/highfly.gif], the hi of the filename highfly.gif also gets highlighted.... Here is the code I am currently using:

$message_post = preg_replace("/$keywords/i", '<span class = "highlight">'.$keywords.'</span>', $message_post);	

so the image tag becomes
[ IMG=http://google.com/images/<span class = "highlight">hi</span>ghfly.gif]
which is of course not what I want. Is there anyway I can check for this?

[drew010]

i might try

$message_post = preg_replace("/\b$keywords\b/i", '<span class = "highlight">'.$keywords.'</span>', $message_post);  

adding the boundary will only hightlight the word if its not a substring of another.

[Adamthenewbie]

thanks, that works great.

Is there an easy way to make it so I keep the same capitalization on the replaced keywords? Like now say I search for the keyword hi, it would match HI but changes it to <span class = "highlight">hi</span>

I guess what you would be best would be to replace it with
<span class = "highlight">HI</span>

[drew010]

havnt tested it but to preserve case, i think the following will do it

$message_post = preg_replace("/\b($keywords)\b/i", "<span class=\"highlight\">$1</span>", $message_post);