Question

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What do ^ and $ mean in a regular expression?

I’m not good at all at regular expression, i know they are so much important but never found the time to study them. Anyway i’m just tring to ensure that, among these strings:

MAX_AGE_60
MAX_AGE_80
...
MAX_AGE_X

where more in general X is a integer, at least one match is found and get the number X. So following the example on PHP documentation i wrote this:

// Starts and ends with the literal 'MAX_AGE_' followed by a group that is a 
// number with at least one digit. Case insensitive
$pattern = '/^MAX_AGE_(?P<max>\d+)$/i';

$test    = 'MAX_AGE_80';
$matches = array();

preg_match($pattern, $test, $matches);
var_dump($matches);

The result is wrong (suprise…):

array (size=0)
  empty

Removing start/end delimiters (^ and $) i get the correct result:

array (size=3)
  0     => string 'MAX_AGE_80' (length=10)
  'max' => string '80' (length=2)
  1     => string '80' (length=2)

So why i can’t force that the string must start and end with that pattern? And how should interpret the result array? I mean indexes 0, 1 and max?

Answer 1

I’m not sure what you’re doing between the parentheses there. Try this:

$pattern = '/^MAX_AGE_[\p{N}]+$/iu';

And the difference between ^$ and not, is that they flag only matches that are at the beginning and/or the end of the LINE

You can use this site to test your expressions (non unicode):
http://www.gskinner.com/RegExr/