Lab #3
CS 2351
UNIX Operating System

Name _________________________________

Section ___________________

Directory and Plain Files The UNIX file system is a flexible and easy to use system that is particularly well suited for software development. The UNIX file system is a tree structure which allows files to be placed into convenient groups by collecting them into a directory file.

A file is a collection of related information. These are also called plain files. Files could be text, or some type of data base with both text and numbers, or it could be a computer program. Ordinary files are organized into special files called directories.

A directory contains zero or more (sub) directories and zero or more files. Directories are used to keep like items together in one place, similar to having a different note book for each class. A plain file corresponds to a leaf node on a tree since a plain file cannot have any successor. A directory file, corresponding to an internal node on a tree, may have one or more successors of either type.

The hierarchical structure of the file system is possible because of the directory files. The entire file system is a single tree with the root of the tree specified as /. The tree structure is like an upside down tree with the root at the top. A reference to the file named / is a reference to the root directory. Each user has a main directory, called the home directory. The home directory is the root of a subtree in the file hierarchy. The name of the user's home directory usually corresponds to the user's login name.

There are some rules for file or directory names. You choose names for any files and directories you make. UNIX file names may contain from one to fourteen of the following characters, in any combination:

Uppercase letters (A to Z)
Lowercase letters (a to z)
Numerals (0 to 9)
Period (.), underscore (_), comma (,)

The file names should NOT contain spaces or any of the following special characters:

& * \ | [ ] {} $ <> ( ) # ? ‘ " / ; ^ ! ~ %

It is always a good idea to choose reasonably short names to save typing. You should also choose names that convey information about the contents of the file. You will be learning many UNIX command names. DO NOT USE command names as file names.

EXAMPLES OF A UNIX DIRECTORY STRUCTURE

Words that are in boxes are directories. Words that are not enclosed in boxes are plain files.

1. The top directory is the root.

2. The first line of directories (bin, contrib, d, k, etc) are called the systems directory. These are similar for all UNIX systems. The boxes that have one letter in them (d, k, p, etc.) are considered partitions. There are many partitions on the SUN machine. There are several students in each partition. Each student is in one of these partitions. 

3. The next row contains other directories. Notice the one marked "srp". This is a person's home directory. Each one of you will belong to a partition and have a home directory. The path name for this particular person is: /d/srp. This is an absolute path name because it starts with the root (/) and gives the entire path name.

4. Each person can have some files in his or her home directory. He or she can also have several directories where other files that are related can be kept. It is a way to keep things organized and easier to find. In this particular example, the person has one directory for MSIS homework and another for Cunix homework. These are then broken down into two other directories, prog and labs. The student can keep programs in the program directory and lab assignments in the labs directory. In each of these directories are files. 

The command pwd (print working directory) can be used to find out what directory you are in.

Type in:             pwd

What is printed out? ___________________________________________________

This should also be the path for your home directory. When you make new directories and change to that directory, your working directory will change.

The mkdir (make directory) command is used to create a new directory. The reason you might make new directories is to keep files that are alike in one directory. An example would be class assignments for certain classes could be kept in one directory. Other class assignments could be in other directories.

Now, make a directory named sample within your own directory by issuing the command:

Next, create another new directory named homework. What command did you use? ____________________________________________

Type in:            ls -l

You should see sample and homework listed. You will see lists of files that look similar to this.  

drwxr-xr-x 2 2351jje 2351jje  512   May 5 08:16  sample 
drwxrw-rw-  2 2351jje 2351jje  512  May 5  08:20 homework 

The cd command allows you to change to a new directory. Change to the directory homework by using the cd command:

What command can you use to check that you are in the new working directory? _______________________________

What is listed now as your working directory?___________________________________

Create these next two items in the homework directory:

    1) Create a new directory called cunix.

    What command did you use to make this directory?______________________________

    2) Create a new file assign1. This file is still in the homework directory. 

    Create assign1 by doing the following:

Notice that you can use the cat command to enter information into a file instead of using the vi editor. This is a short cut method. However, if you make a mistake after you have completed a line and then hit the return key, you cannot make a correction on this file. For very short input files, this can be another method of making a file besides using the  vi editor. When you have finished typing, you press the ctrl and d keys to get back to the prompt.

Type in the following:    ls -l 

Remember that there is always a space after a command and any options that are used. the "l" is a lower case "L" and not the number "1"(one).

What files are listed? ________________________________________________________

Is one of the files a directory?________________

If so, how do you know that it is a directory?______________________________________

In any directory there are two invisible files named "." and "..". These will only show up if you type in the type in the ls -a command. At this time, type in:

You should see the "." and the ".." files. These refer to the current working directory (found by typing in pwd) and its parent respectively. The parent directory is the directory  above the directory you are in at the time. It is one level up on the tree. You can change your working directory to the parent of the current working directory with the command cd .. . Make sure that you leave a space after the cd before you type in the two periods.

Enter the following sequence of commands.

What is printed to the screen?______________________________________________

Your home directory is the parent to the directory "homework".

You can change to your login directory (also called home directory) at any time by typing:

                 cd

When you no longer need a directory, you can remove it by using the rmdir command. The command would be:

First, remove the sample directory that you made. Type in:

Next, try to remove the homework directory. What message did you get when you tried to do this?

__________________________________________________________________________

You should have received an error message saying  rmdir: directory "homework" Directory not Empty.You cannot delete a directory that has files or other directories in it. The files (and directories) must be removed from the directory first (using rm or rmdir). You must return to the directory you want to delete and remove files and any directories in that directory first. Then you must be in the level above (the parent directory) in order to remove the directory.

Return to the homework directory. Remove the directory, homework, by first removing the file and directory from it and then moving up to the parent directory. What commands did you use to remove the directory homework? _________________________________________________________________________

_________________________________________________________________________

Checking out different directories

Make sure that you are in your home directory. Type in:

What is the response?_________________________________________________________

If you are not in your home directory, type in  cd before you do the following. You will now go browsing up the hierarchical structure of the UNIX file system. You will go to the root of the tree and over to some other directories. Type in:

Next, issue the command pwd. What was the result? _________________________________

You are now in the subdirectory that contains the names of other users who are in the same partition as you are. You can find out how many other users have accounts in the same partition as you by issuing the following command:

What was the result?________________________________________________________

The wc command is used for counting the number of lines, words, and characters in a file or directory. The wc has three options:

-c	Characters	This option causes wc to display only the number of characters in a file.
-l	Lines	This option causes wc to display only the number of lines in a file.
-w	Words	This option causes wc to display only the number of words in the file.

If none of the options are listed after the wc, then you will receive three numbers. The first is the number of lines, the second is the number of words, the third is the number of characters. Type in the following:

What was the result? _______________________________________________________

In this particular case, the names make up one word and each line contains one file, so the number of words and the number of lines will be the same.  Next, type in:

What is the working directory now? ___________________________________________

You have reached the root of the tree. Next type in:

You will get a list of the directories that are in the systems directory. You will now go to one of the subdirectories. Next, Issue the command:

cd /class
     or
cd class

You are now in the class directory. This directory contains special subdirectories for different classes. There is one for this class. It is called cs2351. This directory has files that you will use to copy back to your account. The system administrator sets up these special directories so others can access them. Change to the cs2351 directory. 

What commands did you use to do this? _______________________________________________

What answer did you get?  _______________________________________________________   

Some directories are protected so others cannot access them. That is what is happening here.  

Return to your home directory by typing in:

Sometimes you want to print out files. Later your instructor may have you do other assignments that need to be turned in. You can print out files by using the lp command. This command requests that files be sent to a printer. The lp command also uses the -d option for destination. 

NOTE:  If you are at home or somewhere else where you are connected by a modem, the lp command will not work on your home printer. The lp command does not work for local printers.  You can still issue the command from home, but the specified file will be printed at the designated printer on campus.

The command will look like this:

The laser printers in MS 108 are:

                ms108pr1     and  ms108pr2

If you are located in some other lab besides MS 108, there are other printers in the rooms at OSU in Stillwater and also at OSU-Tulsa.  You may need to ask your instructor for names of  other printers.  

If you happen to be in some other room on campus, the printers will have different names. There is usually a sign above the printer telling you the network name. 

You don't have any long files to print out yet. In order to try out the print command, you can copy a file from the newuser directory that has been set up for students and faculty who are new to the Computer Science Department.  This file will be used later in another lab. NOTE: There is a space between the cp and the directory address. One way to do this is to type in the following:

                cp /pub/htdocs/newuser/employee employee

                 request id is printer_1-365 (1 file)

    practice
    filea
    fileb
    filec
    employee
    combine

List out the files to see if they are there. Do not remove any of these files. What command did you use to do this?______________________________________________

Please indicate any areas of this lab that were difficult to understand.