5.5 Identifying and Using Metacharacters
5.5.1 Identifying metacharacters
Metacharacters are keyboard characters with special meaning to the shell. They are a powerful feature of any shell. A general definition of a metacharacter is any keyboard character that is not alphanumeric. Metacharacters are used with many UNIX commands to provide greater flexibility. Some of the metacharacters used with UNIX are similar in function to those used with DOS. The asterisk (*) and the question mark (?) are metacharacters which are also known as wildcards and are used to work with groups of files efficiently. The Figure shows some of the more common metacharacters and a brief description of their primary function. 

It is very important not to use metacharacters when naming files and directories. The dot (.) and underscore (_) are the only two non-alphanumeric characters that are not metacharacters. This is why you can use the dot (.) and the underscore (_) in file names. A hyphen (-), even though it is a metacharacter (used to delineate options in a command line), can also be used in file names.