Special Environment Variables

PATH and its peculiarities.

The 'PATH' variable defines a set of directories in which the shell (and certain system calls) will look for executable files whose names were given without a full path. The 'PATH' may also include special names, such as '.' - which refers to the current directory of the process that launches the new process.

TERM, term and friends.

Defines the type of terminal the user is logged on. Various libraries (terminfo, termcap) use this to determine how to perform on-screen cursor movement, erase the terminal, etc.