10.1 An Overview of Filehandles
A filehandle is the mechanism by which you establish an I/O connection from your Perl program. This typically represents access to a file on your file system but this is by no means the only type of I/O connection where you will use a filehandle. For example the Standard Input and Standard Output streams (STDIN and STDOUT) are filehandles that allow you to read keyboard input and send information to the user.s display.
Perl includes six predefined filehandles two of which will already be familiar to you from the pervious chapters on Input and Output: STDIN, STDOUT, STDERR, DATA, ARGV and ARGVOUT. These filehandles are automatically opened when you run your process so do not need to opened manually. You should, of course, avoid assigning any of these names to your own filehandles.