$re = '/(ABC[#:*$]+(?:\w+[#:*$]+){2}|DEF[#:*$]+(?:\w+[#:*$]+){3})([^#:*$]+)(.+)/';
$str = 'ABC#12#3#LINE1####1234678985$
DEF#XY#Z:1234:1234561230$
ABC#12#3#LINE TWO####1234678985$
DEF#XY#Z:1234:4564561230$
ABC#12#3#3RD LINE####1234678985$
DEF#XY#Z*1234:7894561230$';
$subst = "\1 + replacement + \3";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php