Word Boundary \b php example

word_boundary.php

<?php
  /**
   * Example using Word Boundaries (\b)
   */
   $regex = "/\b4\b/";
   $string = "4, 44, 41, 99, 404, 433, 004, 4";
   preg_match_all($regex, $string, $matches);
   print_r($matches);
   
   /**
    * This will return
    * array(
    *   array(
    *     0 => 4, 
    *     1 => 4
    *   )
    * )
    */
    
  /**
   * If you want to replace only the 4's, not the 14's or the 41's
   */
   $regex = "/\b4\b/";
   $string = "4, 44, 41, 99, 404, 433, 004, 4";
   $replacement = 39;
   $new_string = preg_replace($regex, $replacement, $string);
   echo $new_string;
   
   /**
    * This will return
    * 
    * "39, 44, 41, 99, 404, 433, 004, 39";
    *
    */    
?>