Question

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What regular expression can never match?

how do i write a regular expression which returns false always in php.

i wanted this bcos . i wanted to display a error msg with out a form rule…so i did like this..

if($values['result_msg'] == 'ERROR')
                    {
                    $form->registerRule('just_check','regex','/$^/');                       
                    $form->addRule('abc', 'Please enter valid Model Number.','just_check');
                    }

Answer 1

There are lots of ways to do it:

• /(?=a)b/

This fails to match because it searches for a character which is both a and b.

• /\Zx\A/

This fails to match because the end of the string cannot come before the start of the string.

• /x\by/

This fails to match because a word boundary cannot be between the characters x and y.