Question

In PHP I have some string-tags (pseudo-code):

[TAG_A]              = X
[TAG_B]              = Y
[TAG_X]              = Z

so when I replace these tags in a string:

[TAG_A] and [TAG_B] are connected with [TAG_[TAG_A]]

it should output:

X and Y are connected with Z

The problem lies in the nested tags. It needs to be recursive, where the inner tags are replaced first. All possible tags (with their values) are stored in a large array.

I would like a replace method that not just uses brute force to replace all tags by using foreach on the tags-array, but in fact only searches for []-pairs in the string, and then looks up the value in the tags-array.

Regexes are not the right way, I think, but what is the most efficient way to do something like this?

Answer 1

Replace the tags in the string then check if new tags come up after the process. Run the code again until there are no more tags to be replaced.

$string = '[TAG_A] and [TAG_B] are connected with [TAG_[TAG_A]]';
$search = array(
    '[TAG_A]'   => 'X',
    '[TAG_B]'   => 'Y',
    '[TAG_X]'   => 'Z'
);
$continue = true;
while ($continue) {
    foreach ($search as $find => $replace) {
        $string = str_replace($find, $replace, $string);
    }
    $continue = false;
    foreach ($search as $find => $replace) {
        if (strpos($string, $find) !== false) {
            $continue = true;
            break;
        }
    }
}
echo $string; // prints "X and Y are connected with Z"

Regex solution:

$string = '[TAG_A] and [TAG_B] are connected with [TAG_[TAG_A]]';
$search = array(
    'TAG_A' => 'X',
    'TAG_B' => 'Y',
    'TAG_X' => 'Z'
);
while(preg_match_all('/\[([^\[\]]*?)\]/e', $string, $matches)) {
    $string = preg_replace('/\[([^\[\]]*?)\]/e', '$search["$1"]', $string);
}
echo $string;