phpregexescapingdelimiter

Regular expression displays a Warning when the pattern delimiting character is used inside of a character class

I'm using the following regex to parse a date in dd/mm/yyyy format:

^(0[1-9]|[12][0-9]|3[01])[- /.](0[1-9]|1[012])[- /.](19|20)\d\d$

I've checked it on strfriend and it all looks ok. However, when testing for it in PHP with preg_match it doesn't recognize it:

if(!preg_match("/^(0[1-9]|[12][0-9]|3[01])[- /.](0[1-9]|1[012])[- /.](19|20)\d\d$/",trim($_POST['dob']))){
  $error .= "You must enter a valid date of birth.";
}

This happens with input such as 29/10/1987 and 01-01-2001, and I'm not sure why it doesn't work!

I also get the following warning:

Warning: preg_match() [function.preg-match]: Unknown modifier '.' in /home/queensba/public_html/workers/apply.php on line 18

which I'm not sure how to interpret.

Solution

  • If you use '/' in within your regex, you may not start/end the regular expression with it. Just replace it with '#' for example.

    if(!preg_match("#^(0[1-9]|[12][0-9]|3[01])[- /.](0[1-9]|1[012])[- /.](19|20)\d\d$#",trim($_POST['dob']))){
  $error .= "You must enter a valid date of birth.";
}

    (BTW, Modifiers would come after the final delimiter '#'. So the warning appeared because PHP thought the regex would end after the second '/'.)