php字符串模板变量名替换

需要把字符串中的 {$amount}, {$project} ... 替换为 {$code}

不知道用preg_replace怎么做

* preg.php

<?php
include dirname(__FILE__).'/Str.php';
$s = "您的奖励元已到账，请登录会员中心查看！【xxxx】{\$amount}";

// 把模板变量名替换为code
// $t = Str::replaceBetween($s, 'code', "{\$", "2}");
$t = Str::replaceBetween($s, 'code', "{\$", "}");
var_dump($t);

$s = '您???的{$project}???已成功！【xxxx】';

$t = Str::replaceBetween($s, 'code', "{\$", "}");
var_dump($t);

* Str.php

<?php
/**
 * Created by PhpStorm.
 * User: Mch
 * Date: 2019-11-24
 * Time: 12:59
 */

class Str
{
    /**
     * 把字符串$s ${xxx} 中间的内容替换成 ${yyy}
     * @param $s string 替换前的整个字符串
     * @param $repe string 用来替换的部分字符串
     * @param string $open ${
     * @param string $close }
     * @return string
     */
    public static function replaceBetween($s, $rep, $open = "\${", $close = "}") {
        $i = self::findIndexFollowDelim($s, $open, 0);
        $j = self::findIndexFollowDelim($s, $close, $i);
        // not found
        if ($i < 0 || $j < 0) {
            return $s;
        }
        return substr($s, 0, $i).$rep.substr($s, $j-1);
    }

    private static function findIndexFollowDelim($s, $delim, $startAt=0) {
        $n = strlen($delim);
        $j = 0;
        for ($i = $startAt; isset($s[$i]) && $j < $n; $i++) {
            if ($delim[$j] === $s[$i]) {
                $j += 1;
            } else {
                $j = 0;
            }
        }
        if (!isset($s[$i]) && $j < $n) {
            return -1;
        }
        return $i;
    }

}

* test:
$ php preg.php 
string(82) "您的奖励元已到账，请登录会员中心查看！【xxxx】{$code}"
string(55) "您??的{$code}??已成功！【xxxx】"