Using POSIX regular expressions

Within PHP there are seven functions used for searching strings using POSIX-style regular expressions:

• ereg() -
              This function utilizes the POSIX-style regular expressions to search strings provided for a
match and is case-sensitive. If there is a match, the function returns a TRUE, if the regular expression
does not find a match, a FALSE is returned.

<?php
$phone_number = "1900Atlanta";
if (ereg("[^0-9]",$phone_number)) print "The Phone Number
must contain only numeric digits";
?>

The result of the above php script, which tests for any characters in the $phone_number variable
that are not numeric digits, would be the printing of "The Phone Number must contain only numeric
digits". Another way to use the ereg() function is to utilize the optional parameter regs (the third
parameter) to break up a string. The following demonstrates how this would work:

<?php
$phone_number = "515-435-6789";
$p = ereg("[[:digit:]]\- [[:digit:]]\- [[:digit:]]",
$phone_number, $regs);
print $regs[0]."<br>"; // Outputs the entire phone number
print $regs[1]."<br>"; // Outputs the area code
print $regs[2]."<br>"; // Outputs the first three local
digits
print $regs[3]."<br>"; // Outputs the last four numbers
?>
• eregi() -
               This function is identical to the ereg() function but is case insensitive, meaning it ignores
case distinction when matching alphabetic characters.

<?php
$last_name = "DeMarco";
if (ereg("marco",$last_name)) print "Matched with ereg";
if (ereg("marco",$last_name)) print "Matched with eregi";
?>


The script above would print "Matched with eregi" but would not match with ereg(). This is because
the ereg() function was looking for a lowercase "m" in the $last_name variable, where eregi() did
not care if the "m" was lower or uppercase.