捕获组+数字为PHP [重复]

Question

This question already has an answer here:

• preg_replace: add number after backreference 2 answers

I referred this question - Capture group reference + numeral

I tried with both the options provided there. Here is example code using ECMAScript expression (I guess I need to use this, correct me if I am wrong) -

$string = "box.last_rollout_revision = dummy";

$regex = "/(box\.last_rollout_revision[\s]*=[\s]*)[a-z0-9-_]*([
]*)/";

$test = "234";
$replacementPattern = "$1".$test."$2";

echo preg_replace($regex,$replacementPattern,$string);

Expected output

box.last_rollout_revision = 234

Actual getting

34

P.S. I am trying to replace value against a key in a config file which has several other key-value pairs. I think regex will make it easier in this case. Correct me if I am wrong.

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Answer 1

Change the replacement pattern to

$replacementPattern = '${1}'.$test.'$2';

See the IDEONE demo