Suppose you have two files called foobar and foo.bar . You want to delete foo.bar . Both foobar and foo.bar start with fo , but it was able to complete to foo . If you type in . , then hit Tab again, the shell would be able to fill in the rest of the filename for you. Another function of the shell is environment variables.
Environment variables are a variable key pair stored in the shell's environment space.
This space can be read by any program invoked by the shell, and thus contains a lot of program configuration. PATH Colon separated list of directories to search for binaries. The current shell. The name of the user's terminal. Used to determine the capabilities of the terminal.