从php核心代码分析require和include的区别
main/main.c文件中找到php_message_handler_for_zend函数：
//include输出错误信息时的级别为：E_WARNING
case ZMSG_FAILED_INCLUDE_FOPEN:
php_error_docref(“function.include” TSRMLS_CC, E_WARNING, “Failed opening ‘%s'' for inclusion (include_path=''%s'')”, php_strip_url_passwd((char *) data), STR_PRINT(PG(include_path)));
break;
//require输出错误信息时的级别为：E_COMPILE_ERROR
代码略
总结
和开头PHP手册所说完全一致，require和include的区别在于，出现错误时，一个是error一个是warning。