UNIX Standards and Revisions
Table 1.1 listed many companies that have modified UNIX and that distribute the operating system under some name other than UNIX, such as HP-UX or SunOS. In this book, you will sometimes see two or three different ways to do one task because some types of UNIX computers can do it only the first way, some only the second way, and some only the third. At one company, you may regularly use several different types of UNIX servers, where the commands have such differences. If you connect to a wide area network such as the Internet, you will encounter even more UNIX hosts in which UNIX is slightly different than what you are used to. At first, you may find this variety disconcerting.
Lack of Administration Standards