php 只替换字符串中第一次出现的字符

字符串：abcdefgabchijklmn
查找对象：abc
替换内容：123
最终效果：123defgabchijklmn

$str = "abcdefgabchijklmn";
$needle = "abc";
$result = substr_replace($str,"123",strpos($str,$needle),strlen($needle));
var_dump($result);