此PHP Regex代码有什么问题？

Question

The x modifier code in this tutorial Php regex tutorial gives me the following error:

Warning: preg_match() [function.preg-match]: Unknown modifier ' ' in C:\xampp\htdocs\validation\test.php on line 16
Pattern not found

What's wrong with it?

<?php
// create a string
$string = 'sex'."\n".'at'."\n".'noon'."\n".'taxes'."\n";

// create our regex using comments and store the regex
// in a variable to be used with preg_match
$regex ="
/     # opening double quote
^     # caret means beginning of the string
noon  # the pattern to match
/imx
";

// look for a match
if(preg_match($regex, $string))
        {
        echo 'Pattern Found';
        }
else
        {
        echo 'Pattern not found';
        }
?> 

Answer 1

You have an extra newline in the modifiers because the terminating quote is on a new line after imx , that is why you are seeing unknown modifier ' '

Try changing it to this:

$regex ="
/     # opening double quote
^     # caret means beginning of the string
noon  # the pattern to match
/imx";  // move "; to same line as /imx

Answer 2

PHP gives you the reason for the error in the warning message: Unknown modifier ' ' .

Obviously you are not allowed to have white space in the modifier list after the ending delimiter / in your pattern. You can remove this white space with the trim() function:

if (preg_match(trim($regex), $string))
// ...