可以这样做（参考）

<?php
$allString = "I love Shanghai 123456！";
$searchString = "Shanghai";
$newString = strstr($allString, $searchString);
$length = strlen($searchString);
echo substr($newString, $length);

或者

<?php
$allString = "I love Shanghai 123456！";
$searchString = "Shanghai";
$firstLength = strpos($allString, $searchString);
$length = $firstLength + strlen($searchString);
echo substr($allString, $length);

使用正则匹配：

<?php
$allString = "I love Chongqing 123456!";
preg_match("/Chongqing(?<right>.*)/", $allString, $matches);
print_r($matches);

其中，right只是给匹配的结果命名，最终输出：

Array
(
    [0] => Chongqing 123456!
    [right] =>  123456!
    [1] =>  123456!
)

$str = 'I love guangdong 123456!';
$strDelimiter = 'guangdong';
var_dump(preg_split('/'.preg_quote($strDelimiter,'/').'/',$str));

# 如果确定strDelimiter只出现一次
var_dump(strrev(strstr(strrev($str),strrev($strDelimiter),true)));

# 替换
var_dump(preg_replace('/.+?'.preg_quote($strDelimiter,'/').'/','',$str));