Throughout this text, you will see references to online documents that exist on most UNIX systems. These online documents save the programmer a great deal of time when he is writing programs. Rather than fetch a book and look in the index for the correct page, you can pull up the information within seconds, instead. This electronic documentation can be brought into an editor, or segments of it can be cut and pasted using the normal X Window facilities. For this reason, this text places some emphasis on online manual page references for your convenience.
A document reference will appear in this text in the form open(2), for example. To view the online document for that reference, you would normally enter
$ man 2 open