PHP的$_SERVER是一个系统已定义的数组，
记录了服务的信息
包括：
$_SERVER[HTTP_ACCEPT] => image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/x-shockwave-flash, application/vnd.ms-powerpoint, application/vnd.ms-excel, application/msword, */*
$_SERVER_[HTTP_ACCEPT_LANGUAGE] => zh-cn
[HTTP_ACCEPT_ENCODING] => gzip, deflate
[HTTP_USER_AGENT] => Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0; .NET CLR 2.0.50727) [HTTP_HOST] => localhost
[HTTP_CONNECTION] => Keep-Alive
[PATH] => C:\WINNT\system32;C:\WINNT;C:\WINNT\System32\Wbem;d:\jdk\bin
[SystemRoot] => C:\WINNT [COMSPEC] => C:\WINNT\system32\cmd.exe
[PATHEXT] => .COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH
[WINDIR] => C:\WINNT
[SERVER_SIGNATURE] =>
[SERVER_SOFTWARE] => Apache/2.2.2 (Win32) PHP/5.2.3
[SERVER_NAME] => localhost
[SERVER_ADDR] => 127.0.0.1 //服务器地址
[SERVER_PORT] => 80
[REMOTE_ADDR] => 127.0.0.1 //访客地址
[DOCUMENT_ROOT] => D:/web_root
[SERVER_ADMIN] => gavin1996@126.com
[SCRIPT_FILENAME] => D:/web_root/test.php
[REMOTE_PORT] => 2147
[GATEWAY_INTERFACE] => CGI/1.1
[SERVER_PROTOCOL] => HTTP/1.1
[REQUEST_METHOD] => GET
[QUERY_STRING] =>
[REQUEST_URI] => /test.php
[SCRIPT_NAME] => /test.php
[PHP_SELF] => /test.php
[REQUEST_TIME] => 1192933761
[argv] => Array ( )
[argc] => 0
所有元素都是只读属性，不能被修改
记录了服务的信息
包括：
$_SERVER[HTTP_ACCEPT] => image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/x-shockwave-flash, application/vnd.ms-powerpoint, application/vnd.ms-excel, application/msword, */*
$_SERVER_[HTTP_ACCEPT_LANGUAGE] => zh-cn
[HTTP_ACCEPT_ENCODING] => gzip, deflate
[HTTP_USER_AGENT] => Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0; .NET CLR 2.0.50727) [HTTP_HOST] => localhost
[HTTP_CONNECTION] => Keep-Alive
[PATH] => C:\WINNT\system32;C:\WINNT;C:\WINNT\System32\Wbem;d:\jdk\bin
[SystemRoot] => C:\WINNT [COMSPEC] => C:\WINNT\system32\cmd.exe
[PATHEXT] => .COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH
[WINDIR] => C:\WINNT
[SERVER_SIGNATURE] =>
[SERVER_SOFTWARE] => Apache/2.2.2 (Win32) PHP/5.2.3
[SERVER_NAME] => localhost
[SERVER_ADDR] => 127.0.0.1 //服务器地址
[SERVER_PORT] => 80
[REMOTE_ADDR] => 127.0.0.1 //访客地址
[DOCUMENT_ROOT] => D:/web_root
[SERVER_ADMIN] => gavin1996@126.com
[SCRIPT_FILENAME] => D:/web_root/test.php
[REMOTE_PORT] => 2147
[GATEWAY_INTERFACE] => CGI/1.1
[SERVER_PROTOCOL] => HTTP/1.1
[REQUEST_METHOD] => GET
[QUERY_STRING] =>
[REQUEST_URI] => /test.php
[SCRIPT_NAME] => /test.php
[PHP_SELF] => /test.php
[REQUEST_TIME] => 1192933761
[argv] => Array ( )
[argc] => 0
所有元素都是只读属性，不能被修改
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