Highlight (Search) Key Words in a Text | PHP

Posted on August 30, 2008, under PHP,  Bookmark it

Hello,

This function is useful to highlight words from a simple non-html text. For instance, the search results from your site can be highlighted.

<?php
// Credits: http://www.bitrepository.com/
function hightlight($str, $keywords = '')
{
$keywords = preg_replace('/\s\s+/', ' ', strip_tags(trim($keywords))); // filter

$style = 'highlight';
$style_i = 'highlight_important';

/* Apply Style */

$var = '';

foreach(explode(' ', $keywords) as $keyword)
{
$replacement = "<span class='".$style."'>".$keyword."</span>";
$var .= $replacement." ";

$str = str_ireplace($keyword, $replacement, $str);
}

/* Apply Important Style */

$str = str_ireplace(rtrim($var), "<span class='".$style_i."'>".$keywords."</span>", $str);

return $str;
}

Don’t forget to define your style in the same file or in a separate one (recommended)!

.highlight
{
background: #CEDAEB;
}

.highlight_important
{
background: #F8DCB8;
}

Usage Example:

$str = 'The PHP development team would like to announce the immediate availability of a new PHP version.
The PDT project provides a PHP Development Tools framework for the Eclipse platform.
PHP is especially suited for Web development and can be embedded into HTML.
There are many development tools for PHP.';

$keywords = 'PHP development'; 

// tags from $keywords are automatically stripped
$string = hightlight($str, $keywords); 

echo $string;
?>

As you can see the full string is highlighted with a different color than the words containing it.

Here’s how our example will look like:

IMPORTANT: This function only works for clean text, without any HTML in it (tags, escaping characters).

Your comments and suggestions are welcomed. Feel free to post them!
Good luck!

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15 Replies to "Highlight (Search) Key Words in a Text | PHP"

  1. How to emphasize specific words from a string (text) | PHP Library
    September 6, 2008 at 4:18 AM

    [...] can also check our keywords highlighter if you want to highlight your keywords in your search results. addthis_url = [...]

  2. kL
    October 7, 2008 at 6:10 AM
    Reply

    Disadvantages:

    * it will break HTML if keywords match tag or attribute name
    * it will not find words that use HTML escaping, contain a tag or soft-hyphen.

    You should iterate characters in DOM (or at least match and split whole text nodes via DOM).

  3. Gabriel
    October 7, 2008 at 6:45 AM
    Reply

    This is a function that only matches simple text. You can see that in my example I haven’t used any HTML tags, attribute name or escaping characters. I’ve used it in a search script that had results with only clean text and I didn’t take into consideration that it may match any HTML tag or attribute. However, your observation is good and I will consider improving this snippet. Indeed, you don’t know if people will use it in simple or HTML text.

  4. Loic Hoguin
    October 7, 2008 at 1:30 PM
    Reply

    Wouldn’t this work using str_ireplace instead of regexes? It looks overkill to me. Actually that’s not the only thing in this code that looks overkill…

    Also, CSS directly in HTML is bad practice, just put a class attribute (give it as a parameter to the function) and let people define the style in their CSS.

  5. Gabriel
    October 7, 2008 at 2:04 PM
    Reply

    It seems that the code didn’t save correctly last time and some things haven’t shown up between double quotes. I noticed that and updated the post. I’m sorry for the inconvenience.

    @Loic Hoguin: Yes, it seems like str_ireplace is an alternative in this case. I just forgot about it when I wrote the function.

    Being a short PHP snippet I didn’t want to expand it by separating the CSS style in a file. I was thinking that developers already know how to do that and just added the “style” attribute for highlighting the words.

    Thanks for your comment. I will consider upgrading this post.

  6. Kyle
    February 26, 2009 at 7:58 PM
    Reply

    Just wondering an easy way to not allow it to match substrings in the $str string…only whole words.

  7. Tom S.
    August 3, 2009 at 9:31 AM
    Reply

    This worked GREAT for what I needed. Thanks a lot!

  8. David
    January 28, 2010 at 3:34 PM
    Reply

    Hey, thanks a bunch for this! I wasn’t sure quite how to go about doing this and your example make it very simple to implement.

  9. opa
    September 25, 2010 at 7:00 AM
    Reply

    There is a slight issue with this script it overrides the text words. For example if I search for dog and there is the Dog in the text … this script would output highlighted dog (with lower case d as opposed to the original upper case D) you should consider this as a bug and fix it

  10. opa
    September 25, 2010 at 7:41 AM
    Reply

    This keeps the format of the origianl str for me:

    $char = stripos($str,$keyword);
    if($char!==false)
    $replacement = “<span class=’”.$style.”‘>”.substr($str,$char,strlen($keyword)).”</span>”;

  11. jogesh
    October 16, 2010 at 2:32 PM
    Reply

    thanks man,

    really nice script,

  12. Çetin
    October 29, 2010 at 2:25 PM
    Reply

    I was looking for something like this for a long time..

    Thanks @gabriel and @opa. Very nice and useful function!

  13. Zamshed Farhan
    November 1, 2010 at 4:52 PM
    Reply

    Gr8… I m searching of actually this

  14. Richard
    October 5, 2011 at 5:57 AM
    Reply

    The real challenge would be to highlight the whole word containing a string.

    For example, in a sentence “I like bitrepository a lot” the keyword would be “repository”, but “bitrepository” would be highlithted.

  15. Fabian
    November 18, 2011 at 10:44 PM
    Reply

    I use preg_replace for this, maybe someone might want to use is:

    $str = preg_replace(“/($keyword)(?=[^>]*(<|$))/i",$replacement,$str);

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