PHP preg_replace_callback, replace only 1 backreference?

Question

Using preg_replace_callback, is it possible to replace only one backreference? Or do I have to return the entire thing?

I\'m just trying to wrap the tok

Answer 1

You'll want to use a regex like this, instead:

~\{\$(\w+?)(?:\|(.+?))?\}~i

Then, you can easily see what's being passed to your callback:

$str = 'This is a {$token|token was empty}';
$str = preg_replace_callback('~\{\$(\w+?)(?:\|(.+?))?\}~i', function($match) {
    var_dump($match);
    exit;
}, $str);

Output:

array(3) {
  [0]=>
  string(24) "{$token|token was empty}"
  [1]=>
  string(5) "token"
  [2]=>
  string(15) "token was empty"
}

And from there, you can check if $match[1] is set, and if so, return its value, otherwise, return $match[2]:

$foo = 'foo';
$str = 'Foo: {$foo|not set}, Bar: {$bar|not set}';
$str = preg_replace_callback('~\{\$(\w+?)(?:\|(.+?))?\}~i', function($match) {
    if (isset($GLOBALS[$match[1]])) {
        return $GLOBALS[$match[1]];
    } else {
        return $match[2];
    }
}, $str);
var_dump($str);

Output:

string(22) "Foo: foo, Bar: not set"

Note: I'm making use of $GLOBALS here for demonstration purposes only. I'd suggest making use of PHP 5.4's closure binding, if at all possible, since then you can assign the closure a specific object as context (e.g. your template/view object or whatever contains the variables you're trying to substitute). If you aren't using PHP 5.4, you can also use the syntax function($match) use ($obj), where $obj is your context, and then check isset($obj->{$match[1]}) inside your closure instead.