How can I bold two words around a string within a string, but not overlap sentences?

Question

I need to bold a search term and its context (within a sentence).

Consider the string:

Lorem ipsum dolor sit amet. Consectetuer adipiscing elit.

Answer 1

Hope this helps

$str ="your whole string ";
if(isset($_POST['searchStr']))
{
$searchStr= $_POST['searchStr'];
$str= str_replace($searchStr,''. $searchStr.'',$str);
}
echo "$str";

if you want a case -insensitive replacement use below function

    str_ireplace() - Case-insensitive version of str_replace.