我发现substr_replace方法返回有趣的结果。尤其是在处理URL字符串时。我刚刚写了这个函数。它似乎完全符合我的需要。默认情况下，该函数将返回最长的匹配。

function findOverlap($str1, $str2){
  $return = array();
  $sl1 = strlen($str1);
  $sl2 = strlen($str2);
  $max = $sl1>$sl2?$sl2:$sl1;
  $i=1;
  while($i<=$max){
    $s1 = substr($str1, -$i);
    $s2 = substr($str2, 0, $i);
    if($s1 == $s2){
      $return[] = $s1;
    }
    $i++;
  }
  if(!empty($return)){
    return $return;
  }
  return false;
}

function replaceOverlap($str1, $str2, $length = "long"){
  if($overlap = findOverlap($str1, $str2)){
    switch($length){
      case "short":
        $overlap = $overlap[0];
        break;
      case "long":
      default:
        $overlap = $overlap[count($overlap)-1];
        break;
    }     
    $str1 = substr($str1, 0, -strlen($overlap));
    $str2 = substr($str2, strlen($overlap));
    return $str1.$overlap.$str2;
  }
  return false;
}

获取最大长度匹配的用法：

echo replaceOverlap("abxcdex", "xcdexfg"); //Result: abxcdexfg

要获取第一个匹配而不是最后一个匹配，请像这样调用函数：

echo replaceOverlap("abxcdex", "xcdexfg", “short”); //Result: abxcdexcdexfg

要获取重叠字符串，只需调用：

echo findOverlap("abxcdex", "xcdexfg"); //Result: array( 0 => "x", 1 => "xcdex" )

可以使用substr_replace()和strcspn()：

$string1 = 'abcde';
$string2 = 'cdefgh';

echo substr_replace($string1, $string2, strcspn($string1, $string2)); // abcdefgh

不，没有内置函数，但是您可以轻松地自己编写一个，使用substr和一个循环来查看有多少字符串重叠。