Regex Question

Kold

Hi.

I am stuck with 2 regular expressions.

Firstly, is it possible to return a match if nothing is matched? It seems silly really, but I need to use a regex to check if a number is 11 digits, otheriwise it must be 0. It should be possible using {0}, however it cant really return a match if nothing is matched :bemused:

Secondly, I need to check 2 parts of a string are different. Here is what I used; code[^{\1][/code]However,} the \1 doesnt seem to work inside the [ and ]

Are either of these possible? I just cant work them out.
Thanks!
K.

bradgrafelman

What do you mean to return a match if nothing is matched? If a number is 0 digits, then there is no number. So are you tyring to figure out if a variable is either 11 digits or if it's empty?

Kold

Yes, basically the field can either contain 11 digits, or nothing. Anything else is disallowed. The second one is more important to me though.

tsinka

Hi,

the following pattern should do it:

/^{([0-9]{11})?$/}

What exactly do you mean with

"Secondly, I need to check 2 parts of a string are different"

Regards,
Thomas

Kold

The second part will be like this (instead of 6 chars, will be 11):

123456123456 (not correct as '123456' occurs twice.)
000000111111 (correct as first half doesnt match second half)

Get the idea?
Thanks.
K.

bpat1434

preg_match('#([\d]{6})([\d]{5})#', $string, $matches);
array_shift($matches);

if($matches[0][0] == $matches[1][0])
die("Strings match...");

Weedpacket

preg_match("/(\d{11})\1/", $string);
matches 22 digits, first half identical to the second half.

Kold

bpat1434 wrote:
preg_match('#([\d]{6})([\d]{5})#', $string, $matches);
array_shift($matches);

if($matches[0][0] == $matches[1][0])
die("Strings match...");

I was trying to do it just using a regex, no extra if's etc. This is because the goal is to have the regex's stored in a database, and treated all the same.

Weedpacket wrote:
preg_match("/(\d{11})\1/", $string);
matches 22 digits, first half identical to the second half.

I am trying to make sure the first half is NOT identical to the second half. Therefore, I would modify this to be like the following; B[^\1][/B] BUT, the \1 doesnt seem to work inside the [ and ]

Any ideas?
Thanks.

bradgrafelman

No need to modify the REGEXP, just the logic in the conditional:

if(preg_match("/(\d{11})\\1/", $string))
     die('First half is identical to second half.');
else {
     // halves aren't identical...
}