This is the standard C library
stdlib.h. It gets the value of a specified environment
The default implementation returns
indicating that no environment information is available.
If you re-implement
getenv(), it is recommended
that you re-implement it in such a way that it searches some form
of environment list for the input string,
The set of environment names and the method for altering the environment
list are implementation-defined.
not depend on any other function, and no other function depends
A function closely associated with
called during startup if it is defined, to enable a user re-implementation
getenv() to initialize itself.