getenv()

(PHP 4, PHP 5, PHP 7)

获取一个环境变量的值

说明

获取一个环境变量的值。

使用phpinfo()你可以看到所有环境变量的列表。这些变量很多都在» RFC 3875的范围之内，尤其是章节4.1，"Request Meta-Variables"。

参数

变量名。

设置为 true 以仅返回本地环境变量（由操作系统或putenv()设置）。

返回值

返回环境变量$varname的值，如果环境变量$varname不存在则返回FALSE。如果省略$varname，则所有环境变量都将作为关联数组array返回。

更新日志

注释

如果 PHP 在诸如 Fast CGI 之类的 SAPI 中运行，则此函数将始终返回由 SAPI 设置的环境变量的值，即使已使用putenv()来设置同名的本地环境变量。使用$local_only参数返回本地设置的环境变量的值。

范例

Example #1getenv()例子

参见

• putenv() 设置环境变量的值
• apache_getenv() 获取 Apache subprocess_env 变量
• 超全局变量

Contrary to what eng.mrkto.com said, getenv() isn't always case-insensitive. On Linux it is not: 

From PHP 7.1 => getenv() no longer requires its parameter. If the parameter is omitted, then the current environment variables will be returned as an associative array.
Source: http://php.net/manual/en/migration71.changed-functions.php

As noted on httpoxy.org, getenv() can confuse you in having you believe that all variables come from a "safe" environment (not all of them do).
In particular, $_SERVER['HTTP_PROXY'] (or its equivalent getenv('HTTP_PROXY')) can be manually set in the HTTP request header, so it should not be considered safe in a CGI environment.
In short, try to avoid using getenv('HTTP_PROXY') without properly filtering it.

All of the notes and examples so far have been strictly CGI.
It should not be understated the usefulness of getenv()/putenv() in CLI as well.
You can pass a number of variables to a CLI script via environment variables, either in Unix/Linux bash/sh with the "VAR='foo'; export $VAR" paradigm, or in Windows with the "set VAR='foo'" paradigm. (Csh users, you're on your own!) getenv("VAR") will retrieve that value from the environment.
We have a system by which we include a file full of putenv() statements storing configuration values that can apply to many different CLI PHP programs. But if we want to override these values, we can use the shell's (or calling application, such as ant) environment variable setting method to do so.
This saves us from having to manage an unmanageable amount of one-off configuration changes per execution via command line arguments; instead we just set the appropriate env var first.

As you know, getenv('DOCUMENT_ROOT') is useful.
However, under CLI environment(I tend to do quick check
if it works or not), it doesn't work without modified php.ini
file. So I add "export DOCUMENT_ROOT=~" in my .bash_profile.

Beware that when using this function with PHP built-in server – i.e. php -S localhost:8000 – it will return boolean FALSE.

for quick check of getenv() adding a new env variable -
if you add a new env variable, make sure not only apache but xampp is also restarted.
Otherwise getenv() will return false for the newly added env variable.

When writing CLI applications, not that any environment variables that are set in your web server config will not be passed through. PHP will pass through system environment variables that are prefixed based off the safe_mode_allowed_env_vars directive in your php.ini

SERVER_NAME is the name defined in the apache configuration.
HTTP_HOST is the host header sent by the client when using the more recent versions of the http protocol.

It is worth noting that since getenv('MY_VARIABLE') will return false when the variable given is not set, there is no direct way to distinguish between a variable that is unset and one that is explicitly set to the value bool(false) when using getenv(). 
This makes it somewhat tricky to have boolean environment variables default to true if unset, which you can work around either by using "falsy" values such as 0 with the strict comparison operators or by using the superglobal arrays and isset().

The example on how to fallback produces a syntax error on PHP 5.2:
-bash-3.2$ cat test.php

-bash-3.2$ /web/cgi-bin/php5 test.php 
Content-type: text/html

Parse error: syntax error, unexpected ':' in /home/content/25/11223125/test.php on line 3
On PHP 5.2, one must write
$ip = getenv('REMOTE_ADDR', true) ? getenv('REMOTE_ADDR', true) : getenv('REMOTE_ADDR')

A function returning the remote adress of the visiting browser could look like this:

Note that some adresses are followed by a whitespace and ip2long(getIPfromXForwarded()) would not return the expected result.
Make use of trim() in your scripts, either in the function itself, or the surrounding space of the caller.
Greetings

The function 'getenv' does not work if your Server API is ASAPI (IIS).
So, try to don't use getenv('REMOTE_ADDR'), but $_SERVER["REMOTE_ADDR"].

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