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Due to the fact that PHP's regular expressions are so versatile, many functions that have been designed by PHP developers have been overlooked in the past because the tasks were able to be completed with regular expressions. However, there are two functions that should not be overlooked due to their simplicity in performing a more complex task. • count_chars -                        This built-in function provides information about the number of times that an standard ASCII character appears in the string. <?php $text = "I went to Mississippi for the summer."; $letters = count_chars($text, 1); // 1 counts only the characters that show up more than zero times // 0 is the default and produces the entire listing of standard // ASCII characters, even those not showing up in the string // 2 returns only those ASCII characters that do not show up // 3 & 4 return byte info (all located and all unused, respectively) foreach($letters as $key=>$value)

• ereg_replace()-                          This function is equivalent to ereg() in its case-sensitive searching capabilities; however, it adds the ability to replace the characters it is searching for with new characters instead of just simply locating them. If the search pattern is not found, the string it searched against is unchanged. <?php $url = "MySQL http://www.mysql.com"; print ereg_replace("http://([a-zA-Z0-9./-]+)$", "<a href=\"\\0\">\\0</a>", $url); ?> The script above would change the text "MySQL http://www.mysql.com" to "MySQL <a href="http://www.mysql.com">http://www.mysql.com</a>". This change would allow the http reference to be replaced with the HTML code required to create a web link. The three components of this function include the pattern to search for ("http://([a-zA-Z0-9./-]+)$"), the replacement string ("<a href=\"\\0\&qu

A regular expression is a pattern of characters that are used to match a set of strings when performing searches. Regular expressions, when created, are enclosed in forward slashes and tested against a string. PHP offers functions associated with two types of regular expression tools: POSIX and Perl-style.