What is the usage of the getenv function in PHP?

The getenv function is used to retrieve the value of an environment variable, with the following syntax:

string getenv ( string $varname )

The $varname parameter specifies the name of the environment variable to be retrieved, and the function will return the value of that environment variable.

For example, to retrieve the value of the PATH environment variable, you can use the getenv function like this:

$path = getenv('PATH');
echo $path;

This will output the value of the PATH variable in the current environment. If the environment variable does not exist, the function will return false.