CODEWITHSUNDEEP
phpregexescapingdelimiter
fredley
fredley

Reputation: 33901

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.

Upvotes: 1

Views: 148

Answers (4)

inf3rno
inf3rno

Reputation: 26139

Don't use double quotes for strings, they're for templates. If you have '/' in your pattern, you cannot begin and end it with the same character, do it with "%","#" or any other characters... If you have unicode string, you have to use the "u" flag.

Upvotes: 1

giraff
giraff

Reputation: 4711

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 '/'.)

Upvotes: 4

CrayonViolent
CrayonViolent

Reputation: 32532

Since you are using /.../ as the pattern delimiter you need to escape all other instances of / like \/ alternative is to use a different delimiter like ~

Upvotes: 1

Tim Pietzcker
Tim Pietzcker

Reputation: 336158

The / inside your regex trip up PHP because it thinks they are your regex delimiters.

Try 

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.";
}

Upvotes: 2

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