Most of these commands will be mentioned in more depth in later chapters. You can learn more about the commands by reading the man pages and experimenting on your own. Try running some simple commands such as date, cal, who, whoami, and who am i. Many commands accept arguments on the command line, and some require arguments on the command line. If you try entering a command that requires an argument, the command will usually remind you of the proper usage and then quit.
Many commands also accept command line options that modify the behavior of the command.
Options are separated from the command itself by a space and preceded by a minus sign. The next chapter describes the Unix file system, so let's look at a few basic commands concerning files and directories to briefly introduce you to the concepts of moving around a hierarchical file system. If you have a new account, then no files are listed, but that doesn't mean the directory is empty. You should discover a few hidden files, like .login or .cshrc. These files are used to initialize the shell, or other programs.