Removes an environment variable from the environment.
Note that on some systems, when variables are overwritten, the memory used for the previous variables and its value isn't reclaimed.
You should be mindful of the fact that environment variable handling in UNIX is not thread-safe, and your program may crash if one thread
calls unset_variable while another thread is calling getenv. (And note that many functions, such
as gettext, call getenv internally.) This function is only safe to use at the very start of your program,
before creating any other threads (or creating objects that create worker threads of their own).
If you need to set up the environment for a child process, you can use @get to get an
environment array, modify that with set_variable and
unset_variable, and then pass that array directly to execvpe,
spawn_async, or the like.
| variable |
the environment variable to remove, must not contain '=' |