In the Unix world, environment variables are passed to ALL processes spawned by the parent, including sub-processes. For example, if you log onto a computer, an

In the Unix world, environment variables are passed to ALL processes spawned by the parent, including sub-processes. For example, if you log onto a computer, and your HOME variable is set, then every single process you launch will know your home directory, including processes that launch other processes. It's automatic UNLESS a process explicitly change this value. This does not use any sort of global registry. I used to be an admin of a VAX computer that had 50 simultaneous users logged onto the server, and each user had a different HOME directory. Environment variables also made shell scripts reusable by other users. The file $HOME/special would refer to the "special" file in the user's home directory. Command line arguments are only passed to the one single child process. And if that process wants to launch a new process, it must create it's own command line arguments.