Directory file names are the routes to specific files and are known as path names. A path name starting with a slash begins at the root directory and is called an absolute path name. When a path name begins at the current directory, it is a relative path name. A file named without reference to a directory is understood to reside in the current directory. These are invisible files, because they represent merely links to directories.
Dot refers to the current directory, and therefore is a link to itself.
Dot-dot is the directory's link to its parent directory, one level higher. By specifying a path name using dot-dot you can backtrack and move into another branch of the tree structure. The single dot directory reference can be used as a shorthand symbol. If the current directory is smith , the command mkdir programs would have the same effect. Deletes the programs directory, providing that any files in this directory have first been deleted.