getenv - retrieve an environment variable
Standard C Library (libc, -lc)
getenv(const char *variable);
getenv retrieves the value of the environment variable variable from the current process environment. Unless you implement execve and environment variable passing, the environment used is a default environment compiled into libc.
On success, getenv returns a pointer to the value of the requested variable. This pointer points to internal storage and the contents should not be modified. The contents will in turn be stable until/unless the process environment is modified. If the requested variable is not found, getenv returns NULL.