You re still (Web server certificate) issuing the same command, but now
You re still issuing the same command, but now you re providing additionaldirection on what you want displayed. The -hoption tells duto show you theinformation in terms that humans can read more easily. Now Ms, Ks, and Gsappear next to the numbers so that you can see how big these numbers actu- ally are. But, wait there s more. What if you just want to know the totalamount of disk space this directory and its subdirectories are taking up? That calls for the -sflag: du -sWhat if you want the total for a different directory? Or just one of your subdi- rectories? In my case, I keep a Music subdirectory for the items I have copiedfrom my CDs into Oggs (see Chapter 18). I can type the following command tosee how much hard drive space that directory takes up in a human-readableway rather than have to count zeroes: du -sh ~/MusicIn this example, duis the command name, -shindicates the flags (options), and ~/Musicis an argument. The -shflags can be accompanied by manymore flags that provide various options applicable to the command. Are you wondering where to find all the available options and arguments of aparticular command? Most commands offer manpages, which are discussedin the Help! section, later in this chapter. Another good place to turn is the –helpoption, available with many commands. Note that –helpdis- plays a terse list of options, but it s nice and quick if you already know aboutan option but just can t remember exactly which one it is. Try it by enteringthe following command: du -helpCool, huh? Starting Programs from the ShellThe most obvious, but perhaps not so apparent, use of the shell is to startother programs. Most utilities you use in Linux are separate and distinct exe- cutable programs. Users need a method to start these programs. In the GUI, you can associate an icon with a particular program, and the graphical envi- ronment contains the intelligence to start the program. Note that programsoften require information drawn from environment variables, which are apart of the shell environment. (I discuss environment variables in more detailin the section Working with Variables, later in this chapter.) For this reason, the GUI often calls the intended program via the bashshell. So you see, eventhe GUI finds the shell a necessity although the GUI does its best to hidethis detail from users. 281Chapter 14: Working without the GUI20_