一个例子简要说明include和require的区别

先编辑command.php文件

echo 'hello'.PHP_EOL;

然后编辑console.php文件

for($i=1;$i<=3;++$i){
	require 'command1.php';
}

原本想要包含并执行这个echo，没想到写错了文件名，如果是require，会报出这样的错误：

Warning: require(command1.php): failed to open stream: No such file or directory in console.php on line 4

Fatal error: require(): Failed opening required 'command1.php' (include_path='.') in console.php on line 4
PHP Warning:  require(command1.php): failed to open stream: No such file or directory in console.php on line 4
PHP Fatal error:  require(): Failed opening required 'command1.php' (include_path='.') in console.php on line 4

如果把require改为include

for($i=1;$i<=3;++$i){
	include 'command1.php';
}

会报出这样的错误：

Warning: include(command1.php): failed to open stream: No such file or directory in console.php on line 4

Warning: include(): Failed opening 'command1.php' for inclusion (include_path='.') in console.php on line 4

Warning: include(command1.php): failed to open stream: No such file or directory in console.php on line 4

Warning: include(): Failed opening 'command1.php' for inclusion (include_path='.') in console.php on line 4

Warning: include(command1.php): failed to open stream: No such file or directory in console.php on line 4

Warning: include(): Failed opening 'command1.php' for inclusion (include_path='.') in console.php on line 4
PHP Warning:  include(command1.php): failed to open stream: No such file or directory in console.php on line 4
PHP Warning:  include(): Failed opening 'command1.php' for inclusion (include_path='.') in console.php on line 4
PHP Warning:  include(command1.php): failed to open stream: No such file or directory in console.php on line 4
PHP Warning:  include(): Failed opening 'command1.php' for inclusion (include_path='.') in console.php on line 4
PHP Warning:  include(command1.php): failed to open stream: No such file or directory in console.php on line 4
PHP Warning:  include(): Failed opening 'command1.php' for inclusion (include_path='.') in console.php on line 4

如果使用require_once或者include_once，只要包含路径正确，那么循环只执行一次。

总结：

使用require，如果文件没有包含成功，就会报出一个fatal error，整个程序就中止了。

使用include，如果文件没有包含成功，就会报出一个普通的warning，之后的代码仍会执行。

如果你的Web程序使用了MVC这种对文件包含强依赖的设计方法，请使用require_once。