<?php

$str = "abcdefghijklmn";

$rest = substr($str, 0); // 返回 "abcdefghijklmn"
echo $rest . "<br/>";

$rest = substr($str, 1, 3); // 返回 "bcd"
echo $rest . "<br/>";

$rest = substr($str, -3); // 返回 "lmn"
echo $rest . "<br/>";

$rest = substr($str, -3, 2); // 返回 "lm"
echo $rest . "<br/>";

$rest = substr($str, 1, -3); // 返回 "bcdefghijk"
echo $rest . "<br/>";

$rest = substr($str, -7, -3); // 返回 "hijk"
echo $rest . "<br/>";
?>