- explode: documentation ( source)
<?php
$sometext = "Some text **that is bold!** and some other text";
$string = explode('**', $sometext);
$newStr = '';
$size = count($string);
for ($i = 0; $i < $size; ++$i) {
if (($i % 2 == 0 || $i == 0 )&& $i != $size -1 )
$newStr .= $string[$i]."<b>";
else if($i % 2 != 0 && $i != $size -1)
$newStr .= $string[$i]."</b>" ;
}
echo $newStr;