get_environment_variable Try to get the value of the system environment variable or some
variable in the system registry. Gives NULL when no information
about the variable is available. Under UNIX like system, this is in
fact the good way to know about some system environment variable.
Under Windows, this function also look in the system registery.
set_environment_variable Try to assign the system environment variable with value.
execute_command To execute a system_command_line as for example, "ls -l" on UNIX.
The Result depends of the actual operating system. As an exemple,
this execute feature is under UNIX the equivalent of a system call.
execute_command_line The equivalent of
execute_command without Result.