Placing an exclamation point after the open bracket will signify a pattern that matches none of the characters specified with the brackets. A hyphen between letters that are located in brackets signifies a pattern to match all characters included in the specified range. There is an exception to the filename substitution rules. Any file that begins with a period will not match a pattern. In other words, to see a list of all files that begin with a period, you would have to use the pattern .
Infinite recursion can occur if files have names that include any of the special pattern characters.
Redirecting Input and Output The C shell allows you to redirect standard input, standard output, or standard error to another file or command. These devices are given file descriptors zero through two respectively. File descriptors three through nine are free to use by your applications and can also be redirected as needed. File name substitution or pattern matching does not take place after a redirection symbol. Therefore, care should be taken to ensure files are not created using any of the special pattern characters.