Simple function to return a sub-string following the preg convention. Kind of expensive, and some might say lazy but it has saved me time.

# preg_substr($pattern,$subject,[$offset]) function
# @author   aer0s
#  return a specific sub-string in a string using 
#   a regular expression 
# @param   $pattern   regular expression pattern to match
# @param   $subject   string to search
# @param   [$offset]   zero based match occurrence to return
#                             
# [$offset] is 0 by default which returns the first occurrence,
# if [$offset] is -1 it will return the last occurrence 

function preg_substr($pattern,$subject,$offset=0){
    preg_match_all($pattern,$subject,$matches,PREG_PATTERN_ORDER);
    return $offset==-1?array_pop($matches[0]):$matches[0][$offset];
} 

example: 

             $pattern = "/model(\s|-)[a-z0-9]/i";
             $subject = "Is there something wrong with model 654, Model 732, and model 43xl or is Model aj45B the preferred choice?";

             echo preg_substr($pattern,$subject);
             echo preg_substr($pattern,$subject,1);
             echo preg_substr($pattern,$subject,-1); 

Returns something like:

             model 654
             Model 732
             Model aj45B