";    echo "he drink some ".$beer."s";//he drink some libos    echo "
";    echo "he drink some ${beer}s";//he drink some libos    echo "
";    echo "he drink some {$beer}s";//he drink some libos    echo "
";    //定界符    $string=<<
     

"; //引号套引号 echo '"nihao"';//"nihao" echo "

"; echo "\"nihao\"";//"nihao" //NULL $a=NULL; $b="value"; unset($b); var_dump($a);//NULL var_dump($b);//NULL var_dump($c);//NULL?>