$ls -a . .. a1.txt a2.txt $ls -A a1.txt a2.txt $ls a1.txt a2.txt $
-a, --all do not ignore entries starting with . -A, --almost-all do not list implied . and ..
computer science related Theory Drop
In computing, a hidden directory or hidden file is a directory (folder) or file which file system utilities do not display by default. They are commonly used for storing user preferences or preserving the state of a utility and are frequently created implicitly by using various utilities. Usually the intent is to not "clutter" the display of the contents of a directory with files the user did not create. source :http://en.wikipedia.org/wiki/Hidden_file_and_hidden_directory
current directory indicated by . and previous directory indicated by .. are both hidden