6.0 Basic Unix Commands 

The goal of this section is to give a very brief overview of some of the simplest Unix commands. Upon completion of this section, you should be able to:  All of the commands demonstrated in this section are Unix commands that should be entered in an Xterm window. If you don't have an Xterm window up, you'll need to start one by selecting Xterm from the Workspace Menu. Each of the commands demonstrated in this section should be completed with the <Return> key. 

 
 




6.1 Listing a Directory's Contents 

As a user of the departmental computer system, you have been given a private disk area for storing mail, programs, etcetera, at your discretion. You file system has been supplemented with a few basic default files to provide your account with standard departmental functionality. 

To view the files currently in your disk area, type the ls command...  at the Xterm prompt. You should see something similar to: 

Mail/  bin/  hello 

The first two entries, Mail/ and bin/ are directories, the last entry is a file. 

 The definitions of the two entities can be quite complex, but for now, the standard Folder Analogy will suffice:  The ls command lists the contents of a directory which, in the case above, was your personal directory (know as your "home directory"). This command can accept a number of options (known as arguments) which can change the way the output looks. For example, typing:  Will display: 

total 3 
drwx------ 3 fdrebin 512 Aug 14 14:02 Mail/ 
drwxr-x--- 2 fdrebin 512 Oct 13 1992 bin/ 
-rwxr-x--- 1 fdrebin 782 Oct 13 1992 hello 

The -l option indicates the "long format" should be used to display the current directory. Briefly, this describes the file type and permissions, the number of references to a given file, the owner, the size, the date and time it was last changed, and the name of the file. The implications of all this information will be discussed later in this course. 

 
6.2 Moving into a New Directory 

As mentioned earlier, ls performs its task upon the current directory (also known as the Present Working Directory). To move into another directory, the change directory command (cd) can be given the argument of a new directory like so:  As mentioned before, Unix is a case-sensitive operating system, so the command must be entered exactly as shown above. If you attempt to use all lower case, the machine will display an error message. 

Upon hitting <Return>, you will be moved into the Mail directory. You can confirm this by doing an ls as described above. You should see something similar to:  aliases    context inbox/  nsmail/ 
components drafts/ include sent/ 

You may have noticed that the title at the top of your Xterm window has changed to show "blowfish:/usr/users/fdrebin/Mail" now. This is a convenient way to map your location. 

Looking at the results of the ls command, you will see a directory named nsmail. This is where the Netscape mailer stores your E-mail. To move into this directory, type:  Note the change again in the title bar. You can also determine your current location by typing:  Which stands for Present Working Directory. You will probably see something like this: 

/usr/users/fdrebin/Mail/nsmail 

The first portions is the expanded name of your home directory. While there is some rather important information here, for now, we can safely ignore it. The last two portions give the relevant information; that you are currently in the Mail/nsmail directory of your file system. 

I'm sure now you're ready to move back to your "home" directory. There are several ways we could accomplish that. One way is to backup one directory at a time using a command like:  /usr/users/fdrebin/Mail/nsmail  The .. following the change directory (cd) command indicates the "parent" directory or the directory one level above the current directory. Now the Present Working Directory looks like this:  /usr/users/fdrebin/Mail 

If we issued the same cd command again we'd wind up one level higher, back at the home directory. 

An easier, more convenient way to return your home directory is use a command like:  /usr/users/fdrebin/Mail/nsmail  But wait, we didn't specify where to change directory to. That's right. If you don't specify any arguments to the cd command, it will automatically take you to your home directory. So now the present working directory looks like this:  /usr/users/fdrebin 


 
6.3 Viewing a Text File 

What good is having a bunch of files if you don't know what's in them? No good at all, but ahh, there is a way. You knew there would be. 

Let's look back at what is in our home directory. If your not in the home directory use the cd command as explained in the prior section to return to your home directory. 

 Let's look again at what files you have in your home directory.  Mail/  bin/  hello 

What's that hello file all about? The only way to find out is to see what's in it. 

There's a few ways to view the contents of this file. Here's one:  Will result in the contents of the hello file being display, from beginning to end, on your display. The cat command stands for concatenate and can be used to concatenate two or more files together to form a single file. Our use of the command here, on a single file, has the effect of displaying the file to the screen. 

Notice though that you can't read the top line(s) of the hello file. The top line(s) scrolled off the screen because the contents of the file didn't fit within the window. What to do? You could resize the window as discussed earlier in this tutorial but resizing the window all the time is a pain, and it wouldn't work for really long files. Here's a better way:  This command will result in the contents of the hello file to be displayed one screen at a time. When the contents of the file fills up a screen, the display will be paused to give you a chance to read it. You'll notice that the last line of the display will look something like this: 

--More--(95%) 

This lets you know you haven't reached the bottom of the file yet and that you've seen 95% of the text. (your percentage may be different) When you are ready to see another screen full, or the rest of the file, simply press any key on the keyboard to advance the text; the <Spacebar> works for me. 



6.4 Printing a File 

You can't carry around a Unix workstation with you all the time to view your files (at least not yet). So what do you do if you want to be able to see the content of your files outside of the computer? You print it out on paper of course. 

The command to print a file is lpr. By the way, lpr, is short for Line Printer which is a rather an archaic term for describing a printing device. The lpr command is used like this:  That would print out the hello file to the default printer. Default printer? What's that? When you login at a particular workstation, the system attempts to set your default printer to whatever printer is closest to where your are working. So if you are working in the computer lab at Griffin/Floyd your default printer should be the printer in the lab known as statprn. You can redirect your printing to any other printer on the network by specifying its name as part of the lpr command like this:  Notice the use of the -P argument just before the name of the printer. 

Printing is arguably the most expensive task a computer does. With that in mind, you should consider limiting your printing to those files that are necessary. Our computer system is equipped with a number of sophisticated programs for viewing a wide variety of documents online, without needing to print. 


 
6.5 Piping output to a Printer 

Often, the information you wish to print is either not in a file, or, is not in a location easily accessible. Unix provides an easy method for passing the output of one command as the input of another. This is known as piping. The pipe symbol (|) is used to tell Unix to pass output to a new program. Here's an example:  This will print the contents of the hello file just as we did before. 
 
Earlier we showed how to use the cat command to send the contents of a file to the screen so we could view it. In this example we show how we can use the pipe symbol to redirect output from the cat command as input to the lpr command. Although its not obvious in the example above, you will find many uses for the pipe symbol. Of course, piping is not restricted to just printing files. It may be used in conjunction with a number of programs, which will not be discussed here. 



6.6 Copying a File 

Another useful command allows you to make a copy of a file. There are many reasons why you may want to copy a file. You may want to copy files that are important to you, or copy a file just before you make any major changes to it, or to simply copy a file into a subdirectory. 

The command for copying a file is cp, which of course is short for copy. For the sake of an example, let's copy the hello file using the command:  This creates a new file called hello.bak. If you list the contents of your home directory now it should look something like this:  Mail/  bin/  hello  hello.bak 

Notice the new file. 

You can include directory information as part of the copy destination. So if you wanted to copy the hello file to your bin directory you could issue a command like this:  This tells the copy command that you want to copy the file into the /bin directory off our your home directory. 

The "~" (tilde) is a shorthand method of writing your home directory, and the "/" is used to separate the names of subdirectories off of this main directory. So, ~/bin   references the /bin directory one level below your home directory. You will find the ~/ shortcut a handy to use whenever you need to reference your home directory. 

To verify that the file was copied correctly you can do something like:  hello.bak 

 
6.7 Deleting a File 

Now that we've left a few extra files lying around your file system, its time to clean them up. It is important to keep in mind that disk space is a limited resource. In the course of your computer use, it is important to remove unneeded or obsolete files in a timely manner. This is true for mail messages, programs, data files, etcetera. 

The command we use to delete files is rm, which is short for remove. Looking at the files in our home directory we see:  Mail/  bin/  hello  hello.bak 

We don't need that hello.bak file there anymore so let's delete it using a command like this:  which will remove hello.bak file from our home directory. Another ls command will verify it. 

What about that file we copied to ~/bin ? We probably should delete that one also. We can do that easy enough with a command like:  If we did an ls for the ~/bin   directory, like we did earlier, we would see that the file is now gone. 

One note about deleting files. In a Unix environment, if you accidentally delete a file there is no way you can easily undelete it. That doesn't mean you're doomed. The Systems Manager performs regular daily backups of each user account. If you've inadvertently deleted a file then you should contact the Systems Manager and ask him to restore it for you.