getenv()
getenv() is a PHP native function that reads the value of an environment variable. Called with a name, it returns that variable’s value, or false if it is not set. Called with no argument, it returns an associative array of every currently available environment variable.
Unlike the $_ENV superglobal, whose content is collected once at the start of the script and depends on the variables_order directive, getenv() always queries the environment directly, so it reflects changes made during execution, for example with putenv().
When PHP runs under a SAPI such as FPM or FastCGI, getenv() returns the value set by the SAPI itself, even if putenv() was used to override it locally; passing true as the second, local_only, argument restricts the lookup to locally-set values.
<?php
// read a single environment variable
$home = getenv('HOME');
// read every environment variable
$env = getenv();
putenv('MY_VARIABLE=42');
echo getenv('MY_VARIABLE'); // 42
?>