PHP 冷知识

1，执行Linux命令

<?php
 $a =`ls -a /`;  // execute linux command 
echo '<pre>'.$a;

2.为变量起别名

<?php
 $a = 2;
 $b =&$a;  //为$a起别名
 echo $b; //2
$a = 4;
echo $b;//4
unset($a); //
 $b = 6;
 echo $b; //6

3. 数组运算。+， ==， =， !=, <>, !

<?php
 $a = [1,2,3];
 $b = [4,2,3];

 print_r($a+$b);
 print_r($b+$a);