php的and，or，其实有着then，else的作用，看如下例子

1

<?php
   $b = 'bbbbb';
   $a = 'ggg';
   $a and $c=$a;
   var_dump($c);die;
?>

与下面例子是等价的

<?php
$b = 'bbbbb';
$a = 'ggg';
if($a){
    $c = $a;
}
var_dump($c);die;
?>

2

<?php
  $b = 'bbbbb';
$a = '';
$c = '';
$c and $d=$a or $d=$b;
?>

与下面例子是等价的

if($c){
    $d = $a;
}else{
    $d = $b;
}
var_dump($d);

3

<?php
  $b = 'bbbbb';
  $a = '';
  $c = '';
  $a and ($c and $d=$c or $d='no');
?>

与下面例子是等价的

if($a){
    if($c){
        $d=$c;
    }else{
        $d='no';
    }
}