PATH

Programs may live anywhere and it would be too time consuming for a shell to search all directories. Furthermore, what would happen if there were more than one executable by the same name? The PATH evironment variable contains a colon-delimited list of directories in which commands may be found. When a user types a command that is not builtin, the shell searches all of the directories in the PATH variable, in order. A typical PATH variable is
$HOME/bin:/usr/local/bin:/usr/bin/X11:/usr/bin.

You can see your path (or any variable) by typing
eg1$ echo $PATH Once a command is found, its location is remembered in a hash. Subsequent invocations check the hash before searching directories in PATH. If the PATH variable is changed, the user may have to manually erase the hash with
$ hash -r

[csh: rehash]