PHP Regex to identify keys in array representation - php

Question

I have this string authors[0][system:id] and I need a regex that returns:
array('authors', '0', 'system:id')
Any ideas?
Thanks.

Answer 1

Just use PHP's preg_split(), which returns an array of elements similarly to explode() but with RegEx.
Split the string on [ or ] and the remove the last element (which is an empty string) of the provided array, $tokens.
EDIT: Also, remove the 3rd element with array_splice($array, int $offset, int $lenth), since this item is also an empty string.
The regex /[\[\]]/ just means match any [ or ] character
$string = "authors[0][system:id]";
$tokens = preg_split("/[\]\[]/", $string);
array_pop($tokens);
array_splice($tokens, 2, 1);
//rest of your code using $tokens
Here is the format of $tokens after this has run:
Array ( [0] => authors [1] => 0 [2] => system:id )

Answer 2

Taking the most simplistic approach, we would just match the three individual parts. So first of all we'd look for the token that is not enclosed in brackets:
[a-z]+
Then we'd look for the brackets and the value in between:
\[[^\]]+\]
And then we'd repeat the second step.
You'd also need to add capture groups () to extract the actual values that you want.
So when you put it all together you get something like:
([a-z]+)\[([^\]]+)\]\[([^\]]+)\]
That expression could then be used with preg_match() and the values you want would be extracted into the referenced array passed to the third argument (like this). But you'll notice the above expression is quite a difficult-to-read collection of punctuation, and also that the resulting array has an extra element on it that we don't want - preg_match() places the whole matched string into the first index of the output array. We're close, but it's not ideal.
However, as #AlienHoboken correctly points out and almost correctly implements, a simpler solution would be to split the string up based on the position of the brackets. First let's take a look at the expression we'd need (or at least, the one that I would use):
(?:\[|\])+
This looks for at least one occurence of either [ or ] and uses that block as delimiter for the split. This seems like exactly what we need, except when we run it we'll find we have a small issue:
array('authors', '0', 'system:id', '')
Where did that extra empty string come from? Well, the last character of the input string matches you delimiter expression, so it's treated as a split position - with the result that an empty string gets appended to the results.
This is quite a common issue when splitting based on a regular expression, and luckily PCRE knows this and provides a simple way to avoid it: the PREG_SPLIT_NO_EMPTY flag.
So when we do this:
$str = 'authors[0][system:id]';
$expr = '/(?:\[|\])+/';
$result = preg_split($expr, $str, -1, PREG_SPLIT_NO_EMPTY);
print_r($result);
...you will see the result you want.
See it working