The Unix Environment for Programming (COMP433)

Transcription

1 The Unix Environment for Programming (COMP433) Student's Practical Manual Dr. Mohamed Ben Laroussi Aissa Room 11 I- 13 Spring

2 Textbook

3 Topic # Topic Page 1 Introduction 2 3 The Unix Shell Working with Files and Directories, Basic Unix Commands 4 Common Used Shell Programming Tools 5 Decisions 6 Loops 7 Reading and Printing Data

4 Working with Files and Directories 4 Assignment # 1 Working with Files and Directories Related Chapter: #2 A Quick Review of the Basics STUDENT LEARNING OUTCOMES: Upon completion of this assignment, a successful student will be able to: Be familiar with UNIX file system and basic commands. Execute working with files commands, Execute working with directories commands. Question 1 1. Write a command to display the date and who is logged in. 2. Write a command to get information about yourself.

5 Working with Files and Directories 5 3. Write a command to write directly the following sentence on your computer screen: "University of Nizwa - College of Arts and Sciences" Question 2 Let's suppose that we have one directory "Desktop" and one file "student" inside this directory. Fill in the following table with the appropriate commands. Display the content of Desktop Display the content of the file "student"

6 Working with Files and Directories 6 Question 3 Let us suppose the following directory structure: root documents proposals programs plan sys Figure 1: Directory Structure We have in this directory structure: Directories: document, proposals, programs Subdirectory: plan File: sys 1. Write commands to create all the mentioned directories and the subdirectory.

7 Working with Files and Directories 7 2. Write a command to copy the file sys into a file "sys1" in the directory "programs" 3. Write a command to move the file sys into the directory "proposals" Question 4 a. What will be the effect of the following command? $ cp file1 file2 b. What is the drawback of this approach?

8 Working with Files and Directories 8 c. What will be the effect of the following command? $ ln file1 file2 d. What is the advantage of this approach?

9 Working with Files and Directories 9 Question 5 a. When is it possible to execute a command to remove a directory? b. Write a command to remove the directory "documents" (Figure 1).

10 The Login Shell 10 Assignment # 2 The Kernel and the Utilities Related Chapter: #3 What is the Shell? STUDENT LEARNING OUTCOMES: Upon completion of this assignment, a successful student will be able to: Be familiar with the main UNIX System components. Explain the working method of UNIX System components Explain the executed process when a command is executed. Question 1 a. The Unix systems is itself logically divided into two pieces (see Fig. 1). What are they? Fig. 1: The Unix System

11 The Login Shell 11 Designation Residence Activity Period (a) (b) Table 1: Unix System Components b. Explain the executed process when you execute a command?

12 The Shell Responsibilities 12 Assignment # 4 The Shell Responsibilities Related Chapter: #3 What is the Shell? STUDENT LEARNING OUTCOMES: Upon completion of this assignment, a successful student will be able to: Define the Shell responsibilities, Explain each of Shell responsibilities. Question 1 You know that the shell analyzes each line you type in and initiates execution of the selected program. But the shell also has other responsibilities, as outlined in Fig. 1. a. Explain briefly shell responsibilities.

13 The Shell Responsibilities 13 Fig. 1: The Shell's Responsibilities

14 The Shell Responsibilities 14

15 The Shell Responsibilities 15

16 The Shell Responsibilities 16 Assignment # 4 Common Used Shell Programming Tools Related Chapter: #4 Tools of the Trade STUDENT LEARNING OUTCOMES: Upon completion of this assignment, a successful student will be able to: Define the Shell responsibilities, Explain each of Shell responsibilities. Question 1 You know that the shell analyzes each line you type in and initiates execution of the selected program. But the shell also has other responsibilities, as outlined in Fig. 1. a. Explain briefly shell responsibilities.

17 The Shell Responsibilities 17

18 Command Files 18 Assignment # 5 Command Files Related Chapter: #5 And Away We Go STUDENT LEARNING OUTCOMES: Upon completion of this assignment, a successful student will be able to: Change file permissions and make a file executable, Execute the content of a file. Insert comments or remarks inside a program Observation 1 Before you can execute a program, you must change the file's permissions and make it executable. This is done with the change mode command chmod. To add execute permission to the file file1, you simply type: chmod +x file1 The +x says make the file(s) that follow executable. The shell requires that a file be both readable and executable by you before you can execute it. Before Executing chmod -rw-rw-r-- After Executing chmod -rwxrwxr-x

19 Command Files 19 Observation 2 A shell program can be typed directly at the terminal, or you can first put any commands at all inside a file, make the file executable, and then execute its contents simply by typing its name to the shell. It's that simple and that powerful. Example 1 Suppose that you need to find out the number of logged-in users several times throughout the day. It's not unreasonable to type in the preceding pipeline each time you want the information, but for the sake of example, let's type this pipeline into a file. We'll call the file number_users (number of users), and its contents will be just the pipeline shown previously: who wc 1 pwd Now, let us make the file number_users executable: chmod +x number_users Now, let us execute the file number_users: $ sh number_users Comments The shell programming language would not be complete without a comment statement. A comment is a way for you to insert remarks or comments inside the program that otherwise have no effect on its execution. Whenever the shell encounters the special character # at the start of a word, it takes whatever characters follow the # to the end of the line as comments and simply ignores them. If the # starts the line, the entire line is treated as a comment by the shell. Here is an example of valid comments: who wc 1 # count the number of users#

20 Command Files 20 Exercises Question 1 Write a program called numberfiles to display the number of files in your current directory. Type in the program and test it out.

21 Command Files 21 Question 2 Write a program called whos to display a sorted list of the logged-in users. Just display the usernames and no other information. Type in the program and test it out.

22 Variables 22 Assignment # 6 Variables Related Chapter: #5 And Away We Go STUDENT LEARNING OUTCOMES: Upon completion of this assignment, a successful student will be able to: Use variables, Display values of variables, Use null value, Substitute filenames and variables. Solve exercises related to these subjects. Observation 1 (Material Adapted from the textbook) Like virtually all programming languages, the shell allows you to store values into variables. A shell variable: begins with an alphabetic or underscore (_) character, is followed by zero or more alphanumeric or underscore characters. To store a value inside a shell variable, you simply write the name of the variable, followed immediately by the equals sign =, followed immediately by the value you want to store in the variable: variable=value Observation 2 A few important points here: Spaces are not permitted on either side of the equals sign. Keep that in mind, especially if you're in the good programming habit of inserting spaces around operators. In the shell language, you can't put those spaces in. Unlike most other programming languages, the shell has no concept whatsoever of data types. Whenever you assign a value to a shell variable, no matter what it is, the shell simply

23 Variables 23 interprets that value as a string of characters. So when you assigned 1 to the variable count previously, the shell simply stored the character 1 inside the variable count, making no observation whatsoever that an integer value was being stored in the variable. If you're used to programming in a language such as C or Pascal, where all variables must be declared, you're in for another readjustment. Because the shell has no concept of data types, variables are not declared before they're used; they're simply assigned values when you want to use them. As you'll see later in this chapter, the shell does support integer operations on shell variables that contain strings that are also valid numbers through special built-in operations. Because the shell is an interpretive language, you can assign values to variables directly at your terminal. Displaying the Values of Variables The echo command is used to display the value stored inside a shell variable. To do this, you simply write echo $variable The $ character is a special character to the shell. If a valid variable name follows the $, the shell takes this as an indication that the value stored inside that variable is to be substituted at that point. Observation 3 Even the name of a command can be stored inside a variable. Because the shell performs its substitution before determining the name of the program to execute and its arguments, it scans the line. Observation 4 Remember that a dollar sign must always be placed before the variable name whenever you want to use the value stored in that variable. The Null Value When you try to display the value of a variable that has no value assigned to it, you don't get an error message. Observation 5 A variable that contains no value is said to contain the null value. It is the default case for variables that you never store values in. When the shell performs its variable substitution, any values that are null are completely removed from the command line, without a trace.

24 Variables 24 Filename Substitution and Variables When the shell reads this command it does not store the character * into the variable x, but will store the names of all the files in your current directory into the variable x. The precise sequence of steps that occurred when When the following command x=* echo $x was executed is as follows: 1. The shell scanned the line, substituting * as the value of x. 2. The shell rescanned the line, encountered the *, and then substituted the names of all files in the current directory. 3. The shell initiated execution of echo, passing it the file list as arguments.

25 Variables 25 Exercises Question 1 Fill in the following table, to show the effect sum="" sum=' ' sum= sum=" " Question 2 Suppose that we executed the following command: number=100 Thereafter we executed the following command: $echo There are $number students in Section 1 What would be the effect of the previous command? Question 3 What would be the effect of the following commands? $ command=sort $ $command names

26 Variables 26 Question 4 Suppose that you entered the following commands: $ command=wc $ option=-l $ file=names $command $option $file a. Explain the order of operations executed by the shell when it reads the last command ($command $option $file). b. What would be the effect of the last command ($command $option $file)? Question 5 Suppose that we did not assign a value to variable1. What would be the effect of the following command? $ wc $variable1 -l $ variable1 $ variable1 names

27 Decisions 27 Assignment # 7 Control Structures Related Chapter: #8 Decisions STUDENT LEARNING OUTCOMES: Upon completion of this assignment, a successful student will be able to: Define case command structure Implement case command in programs. Exercises Question 1 The year seasons are distributed according to Table1. Write a shell program using the case command where the user inputs the month and the corresponding season will be printed on the screen. # Period (From Month1 to Month2) Season Summer Autumn Winter Spring Table 1 Example: Input: 1

28 Decisions 28 Output: Season: Winter

29 Iterations 29 Assignment # 8 Iterations Related Chapter: #9 'Round and 'Round She Goes STUDENT LEARNING OUTCOMES: Upon completion of this assignment, a successful student will be able to: Define loop structures Implement loops in programs Exercises Question 1 a. Draw a flowchart, to calculate the following summations: b. Write a program to calculate the previous S using for command c. Write a program to calculate the previous S using while command

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32 Iterations 32 Question 2 a. Draw a flowchart, to calculate the following summations: b. Write a program to calculate the previous summations

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34 Iterations 34 Question 3 a. Draw a flowchart, to calculate the following summations: b. Write a program to calculate the previous summations

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