Winter Training, December 2011 Unix and Shell Programming     Department of COE and SE,    Delhi Technological UniversityI...
ContentsUNIT 1: INTRODUCTION TO UNIX ..........................................................................3UNIT 2: SH...
UNIT 1: INTRODUCTION TO UNIX1. THE UNIX OPERATING SYSTEM – AN OVERVIEW.................................72. UNIX COMMANDS.....
COE                                                                                                                    Uni...
COE                                                                             Unit 1, Lesson 1  1. The UNIX Operating Sy...
COE                                                                              Unit 1, Lesson 11.2.1 Typical hardware co...
COE                                                                              Unit 1, Lesson 1          The OS also wor...
COE                                                                        Unit 1, Lesson 1Self-Check Questions1. A ______...
COE                                                                               Unit 1, Lesson 1          Software Distr...
COE                                                                      Unit 1, Lesson 11.5   UNIX Operating System – Att...
COE                                                                                   Unit 1, Lesson 1         The Comman...
COE                                                                            Unit 1, Lesson 1             The User Comma...
COE                                                                            Unit 1, Lesson 1          The login ID is t...
COE                                                                         Unit 1, Lesson 1      There is a simple scheme...
COE                                                                           Unit 1, Lesson 11.8.1 Command Options and Ar...
COE                                                                      Unit 1, Lesson 1      13. telnet      14. system ...
COE                                                                                                                   Unit...
COE                                                                                                              Unit 1, L...
COE                                                                       Unit 1, Lesson 2                             2. ...
COE                                                                          Unit 1, Lesson 2         Information        ...
COE                                                                   Unit 1, Lesson 22.4.1 mv command      The mv command...
COE                                                                           Unit 1, Lesson 2            bash> ftp mitser...
COE                                                                     Unit 1, Lesson 22.6.2 du – Disk usage      This co...
COE                                                                       Unit 1, Lesson 27. On a multi-user system, there...
COE                                                                      Unit 1, Lesson 22.8.2 & - Running process in back...
COE                                                                        Unit 1, Lesson 213. If it is required to know t...
COE                                                                      Unit 1, Lesson 22.9.6 history command      This c...
COE                                                                       Unit 1, Lesson 2Self-Check Questions14. An _____...
COE                                                                                                                      U...
COE                                                                             Unit 1, Lesson 3                          ...
COE                                                                           Unit 1, Lesson 33.2.2 Filename Extensions   ...
COE                                                                          Unit 1, Lesson 3File Type      Regardless of ...
COE                                                                        Unit 1, Lesson 33.5   Path to a file3.5.1 The r...
COE                                                                                    Unit 1, Lesson 3      The cp comman...
COE                                                                            Unit 1, Lesson 3           bash> ls -l     ...
COE                                                                        Unit 1, Lesson 3      bash> ls -l      drwxr--r...
COE                                                                              Unit 1, Lesson 3         The first octal...
COE                                                                       Unit 1, Lesson 3         Example usage          ...
COE                                                                       Unit 1, Lesson 33.12 Terminal questions      1. ...
COE                                                                                                                  Unit ...
COE                                                                                                               Unit 1, ...
COE                                                                            Unit 1, Lesson 4                           ...
COE                                                                       Unit 1, Lesson 44.3   How Vi Handles The Files  ...
COE                                                                          Unit 1, Lesson 44.5.3 Switching between comma...
COE                                                                         Unit 1, Lesson 44.6.2 The GOTO Command      So...
COE                                                                           Unit 1, Lesson 4       or arrow key; such as...
COE                                                                        Unit 1, Lesson 44.8.1 Delete Text (d, D)      T...
COE                                                                      Unit 1, Lesson 4             Replace             ...
COE                                                                         Unit 1, Lesson 44.9.2 Insert Command (i, I)   ...
Unix shell program training
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A training course in UNIX shell programming. with exercises.

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  1. 1. Winter Training, December 2011 Unix and Shell Programming Department of COE and SE, Delhi Technological UniversityInstructor: Divyashikha Sethia
  2. 2. ContentsUNIT 1: INTRODUCTION TO UNIX ..........................................................................3UNIT 2: SHELL SCRIPTING..................................................................................... 63UNIT 3: ADVANCED SHELL SCRIPTING, SED, AND AWK .................. 143
  3. 3. UNIT 1: INTRODUCTION TO UNIX1. THE UNIX OPERATING SYSTEM – AN OVERVIEW.................................72. UNIX COMMANDS................................................................................................... 213. UNIX FILE SYSTEM ................................................................................................ 334. THE VI TEXT EDITOR ............................................................................................ 45
  4. 4. COE Unit 1, Lesson 1LESSON 1 T HE UNIX OPERATING S YSTEM – AN OVERVIEW1. THE UNIX OPERATING SYSTEM – AN OVERVIEW .................................................7 1.0 OBJECTIVES ...............................................................................................................7 1.1 INTRODUCTION ...........................................................................................................7 1.2 INTRODUCTION TO THE COMPUTERS .........................................................................7 1.2.1 Typical hardware components of a computer.................................................8 1.3 OPERATING SYSTEM..................................................................................................8 1.3.1 Virtual Memory.....................................................................................................9 1.4 UNIX OPERATING SYSTEM .................................................................................... 10 1.4.1 History of UNIX ................................................................................................. 10 1.4.2 Importance of UNIX ......................................................................................... 11 1.5 UNIX OPERATING SYSTEM – ATTRIBUTES AND COMPONENTS ............................ 12 1.6 STARTING WITH UNIX............................................................................................. 14 1.7 CHANGING YOUR PASSWORD ................................................................................ 15 1.8 ENTERING COMMANDS IN THE UNIX SYSTEM ....................................................... 16 1.8.1 Command Options and Arguments ............................................................... 17 1.9 SUMMING UP........................................................................................................... 17 1.10 ANSWERS TO THE SELF CHECK QUESTIONS ........................................................... 17 1.11 TERMINAL QUESTIONS............................................................................................. 18 1.12 REFERENCES .......................................................................................................... 18
  5. 5. COE Unit 1, Lesson 1 1. The UNIX Operating System – An OverviewUse and influence of computers has been steadily increasing in the last fewdecades. Today, computers play a pivotal role in all walks o f life. An operatingsystem (OS) is a core component of the computer system. An operating system letsa computer function as multi-user, multitasking and multithreading environment, thusaugmenting the power of the computer. UNIX is an operating system that offers itsusers all these capabilities along with numerous other features. In this lesson we willlook upon the features and components of the UNIX system that make it very usefuland popular. In the subsequent lessons we will explore the features and componentsof UNIX in more details.1.0 Objectives After going through this lesson, you will be able to  Understand the concepts of the Operating System  Understand what is the UNIX Operating Systems  Understand the importance and popularity of UNIX Operating System  Understand how to start working on a UNIX machines1.1 Introduction In the modern age, we have seen the computer doing wonders, from children playing games to the scientists launching satellites; we can clearly see that the computers are playing a important role. It is the operating system that has made the computing in the modern world possible and efficient.1.2 Introduction to the computers Unlike calculator, a computer carries out user specified tasks. An inherent power provided by a computer is that it can be programmed to do variety of tasks. Computers are mostly general purpose computers in the sense that a computer can be used to play a game and the same computer can be used to perform a circuit simulation. A computer consists of hardware and software. A computer can be defined as a programmable machine which responds and executes a list of instructions. These lists of instructions are called programs. The hardware components are the physical components and software is data o r instruction. 7
  6. 6. COE Unit 1, Lesson 11.2.1 Typical hardware components of a computer Hardware components in computer are what you can see and touch.  Memory: Enables the computer to store the temporary data and instructions. This is used in the computer during the execution of various instruction sets. While evaluating the following expression, the intermediate results are stored in memory Sum = 2 + 1 + 3 * 4  Mass storage devices: These are used for the bulk storage of data, such as, disk drives and tape drives.  Input devices: Interface to take the instructions from the user to the computer. Commonly used input devices are keyboard, mouse, web camera, etc.  Output Devices: Display the results of the instruction processing done by the computer. Commonly used are display monitors and the printers.  Central Processing Unit (CPU): The brain of the computer in which all the processing is done. It reads the data from memory or input and executes the instructions. CPU consists of ALU (Arithmetic Logic Unit) and CU (Control Unit). ALU is responsible for all calculations and CU is responsible for getting instructions and data for execution. Working with the hardware components alone is very difficult because their controls are very cryptic. Instead, software components are used to drive the hardware components. The operating system is also one such software.1.3 Operating System An Operating System (OS) is an important program that runs on the computer. An operating system performs the very basic tasks, such as recognizing inputs from the user, sending outputs to the display, keeping track of file and directories on the disk, and controlling the peripheral devices such as the disk drivers and printers.8
  7. 7. COE Unit 1, Lesson 1 The OS also works as a traffic cop - it makes sure that different program and users running at the same time do not interfere with each other. The operating system is also responsible for security and blocking unauthorized users. Operating systems can be classified as follows:  Multi-user: Allows multiple users to use computers at the same time.  Multiprocessing: Supports running parts of a program in parallel.  Multitasking: Allows multiple programs to run concurrently on a single CPU.  Multithreading: Allows different parts of a single program to run concurrently. Operating systems provide a platform on which other programs, called application programs, can run. The application programs must be written to run on a particular operating system. Your choice of operating system, therefore, determines to a great extent the applications you can run. For PCs, the popular operating systems are DOS, OS/2, Windows and Linux.1.3.1 Virtual Memory Programs that run on a computer may need more memory than what is available physically on that computer. Many operating systems provide an illusion to the user of much larger memory. This is done by loading only partial program and data in physical memory. Only the parts that are needed for current execution are brought into physical memory. So, bigger programs can be run even if physical memory is small. 9
  8. 8. COE Unit 1, Lesson 1Self-Check Questions1. A ____________ is a prerecorded set of instructions, which is executed b y the computer to perform some task.2. A computer is a specific purpose machine that can not be tweaked to perform some other tasks. (True/False)3. The operating systems keep the temperature inside the computer down, so that the functioning is proper. (True/False)4. A ___________ system allows running parts of a program in parallel, on more than one CPU.5. In a _______________ system, a large number of users can use the system concurrently.6. The ____________ memory is an imaginary memory which is used by the Operating System to get a larger address space.1.4 UNIX Operating System1.4.1 History of UNIX The UNIX operating system found its beginnings in MULTICS, which stands for Multiplexed Operating and Computing System. The MULTICS project began in the mid 1960s as a joint effort by General Electric, Massachusetts Institute for Technology and Bell Laboratories. In 1969 Bell Laboratories pulled out of the project. One of Bell Laboratories people involved in the project was Ken Thompson. He liked the potential MULTICS had, but felt it was too complex and that the same thing could be done in simpler way. In 1969 he wrote the first version of UNIX, called UNICS. UNICS stood for Uniplexed Operating and Computing System. Although the operating system has changed, the name stuck and was eventually shortened to UNIX. Ken Thompson teamed up with Dennis Ritchie, who wrote the first C compiler. In 1973 they rewrote the UNIX core (called kernel) in C. The following year a version of UNIX known as the Fifth Edition was first licensed to universities. The Seventh Edition, released in 1978, served as a dividing point for two divergent lines of UNIX development. These two branches are known as SVR4 (Release 4) and BSD. Ken Thompson spent a years sabbatical with the University of California at Berkeley. While there are two graduate students, Bill Joy and Chuck Haley, wrote the first Berkeley version of UNIX, which was distributed to students. This resulted in the source code being worked on and developed by many different people. The Berkeley version of UNIX is known as BSD, Berkeley10
  9. 9. COE Unit 1, Lesson 1 Software Distribution. From BSD came the VI editor, C shell, virtual memory, Send mail, and support for TCP/IP.1.4.2 Importance of UNIX During past 25 years the UNIX OS has evolved into powerful, flexible, and versatile and robust operating system. It serves as the operating system for variety of computers , for single user personal computers , engineering workstation , multi-user microcomputers, minicomputers, mainframes, super computers and as well as special application devices . There are approximately 20 million machines now running UNIX and more than 100 million users, and this popularity and rapid growth is estimated to be increased further. The success of UNIX is due to many factors including its portability to a wide range of machines, its adaptability and simplicity, the wide range of tasks it can perform, its multi-user and multitasking nature, and its suitability for networking. What follows is a description of the features that have made UNIX system so popular.  Multi-user and Multitasking abilities The UNIX OS allows the use of a single computer by many users. It is also a multitasking system that is it allows more than one application to be run on the same computer at the same time.  Powerful command set The UNIX OS provides a consistent and powerful set of commands that has made it very useful particularly for the technical people .  Combining commands The UNIX provides constructs like pipes and redirection of commands which enables the user to create his own powerful utilities from UNIX commands.  Excellent environment for Networking UNIX offers program and utilities that provide the services needed to build networked applications - the basis for distributed, networked computing. With networked computing, information and processing is shared amongst different computers in a network. It is useful in client server computing where the machines on the network can be client and servers at the same time. UNIX system is used as the base system for the development of the internet services and the growth of internet.  Portability The UNIX system is far easy to be ported to new machines than other operating systems. The fact that, it is portable to almost any computer, results from its being almost entirely written in C programming language. 11
  10. 10. COE Unit 1, Lesson 11.5 UNIX Operating System – Attributes and Components The UNIX operating system is made up of several major components. Some of these components are the commands, the file system, the shell, the kernel and the commands.12
  11. 11. COE Unit 1, Lesson 1  The Commands and User Programs UNIX provides a number of built-in commands and in addition user programs can also run.  The File System The basic unit that stores information in the UNIX system is called a file. The UNIX file system provides a logical method of organizing files. Files are organized in a hierarchical file system where the files are grouped together in a directory. Example: Hierarchical File Structure /dtu/COE_Course/COE_101/schedule Here ―dtu‖ is the parent directory which is in ‗/‘ root and other directories are in it An important simplifying feature of the UNIX system is the wa y it treats the files. For example, physical devices are treated as files, this permits the same command to work for an ordinary file or a device i.e. same command can be used to write to a file and printer.  The Shell and shell scripts The shell is the command interpreter in the UNIX operating system. It reads the user specified commands and interprets them as requests to execute a program or a set of programs, which it then arrange to carry them out. Shell also provides a programming language. Shell scripts are covered in subsequent chapters of this unit.  The kernel The kernel is the core of the OS. The kernel interacts directly with the hardware through a set of programs called the device drivers that are built into the kernel. It provides the set of services that can be used by the other programs; also it safeguards these programs from hardware layers. The major functions of the kernel are to maintain the file system, manage memory, access control to the computer, and handle the interrupts (these are the signals to terminate the processes, ctrl + C is a common example)., error handling, I/O handling which enables the computer interaction with the peripheral devices such as printers, monitors, storage devices, etc.). Programs use kernel through the system calls. For example, if the user wants some file to be opened then the program generates a system call to open the directories and then the files. The figure below shows the relationship amongst various components of the UNIX file system. 13
  12. 12. COE Unit 1, Lesson 1 The User Commands The Shell The Kernel Hardware Components of UNIX operating system (shown in gray).Self-check Questions7. UNIX is a multi-user OS and also possesses multitasking abilities. (True/False)8. The first version of the UNIX Operating System was known as _____________.9. The file system in a UNIX Operating System is a hierarchical structure. (True/False)10. The ____________ in a UNIX Operating System is used to interact with the hardware and executes the user commands and program.11. The command interpreter in the UNIX system is called ___________.12. The programs in the UNIX systems interact using the __________ calls with the kernel to perform the tasks.1.6 Starting with UNIX This section is dedicated to the learning of how to log into a UNIX system and how to change password on a UNIX system. We will touch the details of the different types of system configurations and how we can log on to systems having these configurations.  Selecting a login Every UNIX user on a multi-user system is recognized by a login name which is the only identity he has on the system. This is to be set before you use a multi-user or a single user UNIX system, to log onto the system. UNIX provides excellent built-in security. Therefore no users are permitted unless they are identified. For this identification, each user has a login ID.14
  13. 13. COE Unit 1, Lesson 1 The login ID is typically allocated by an authority (known as the system administrator). The system administrator is also responsible to add new users to the system and provide them a login name and an initial work enviro nment and password on the computer. UNIX shows a login prompt initially. User needs to type-in his login ID. Then the password prompt comes. After you correctly type in the password, you get logged into the system. The example below shows this process. login: akash password: ―akash‖ is the user login name. Note to keep password secure, it is not displayed when you type it.  Connecting to the UNIX System In a multi-user system you have to contact the system administrator as to how you can connect to the system using your PC or terminal. Your PC can be directly wired to a computer or it can be connected via LAN. Direct Connect - This is a method of connecting to UNIX machines when there is a single machine. Dial-in Access - You can dial in to the UNIX network using a modem, use terminal emulators to get the UNIX prompt. Local Area Network (LAN) - LAN is a client server model. Connect to the server using the client workstation and use the UNIX capabilities. IP Networks Using IP networks like internet one can connect to some remote machines using telnet capability of UNIX.1.7 Changing Your Password Your password is very important information that you must not share with anyone. You must change it regularly (say once in 2 months) and also should remember it (you must not write it on paper). Your password should contain 6 to 8 letters and should not simply be your name, your date of birth, etc. Your password should also contain at least one non alphabet (maybe a number). To change the password of your login you can use the passwd command. bash> password password: Changing password for sushobhit Old password: New Password: Re-enter new password: bash> 15
  14. 14. COE Unit 1, Lesson 1 There is a simple scheme to create complex passwords and still remember them! All you do is to take the first letters of a line of your favorite poem or song and add a number or symbol to make a complex password. Here is an example: Say you pick the like ―Twinkle twinkle little star‖. Take the first letters to makes a string Ttls. And suppose your favorite symbol is = (equal sign) and favorite number is 2 so you append these to the string to make your complex password as Ttls2=. You can see that for anyone else it will too hard to find out while it is very easy for you to remember. NOTE: If you forget your password it cannot be retrieved even by the system administrator. The only remedy in such cases is that the system administrator can reset the password.Self-Check Questions13. ________________ is the program which is used to connect to the UNIX system from a remote system.14. ___________________ in a multi-user system is the person who is responsible for maintaining the system.15. Get the odd one out To connect to a UNIX system one of the following measures can be used a. Dial-in access b. IP Networks c. LAN d. System Calls16. If you forget your password system administrator can give you permissions. (True/False)1.8 Entering Commands in the UNIX System UNIX provides numerous commands. When the user types some command on UNIX prompt then the shell invokes the program for the command, the command program can invoke many system calls, these calls then interacts with the hardware.16
  15. 15. COE Unit 1, Lesson 11.8.1 Command Options and Arguments UNIX system has a standardized comma nd syntax that is applicable to almost all the UNIX commands. Every command has some base functionality and additional functionality that are provided by the command line arguments. For Example, the ls command can be used to list the contents of a directory. bash> ls README 2134.tar.gz game_scores game_schedule Now let‘s use ls command with some option bash> ls –l -rw-r--r-- 1 anmol friends 10777 Mar 30 16:26 README -rw-r--r-- 1 achint friends 21483 Feb 28 17:39 2134.tar.gz drwxr-xr-x 2 amit friends 4096 Dec 12 16:41 game_scores This example shows the usage of –l argument of ls command, which outputs thedrwx------ 3of ls command. 4096 May 10 2006 long format arat friends game_schedule Another command that is frequently used is ‗man‘ command. This is used to displays the manuals of different commands.1.9 Summing Up An operating system is the most important software in any computer as it fills the communication gap between a user and the underlying hardware. UNIX operating system with its unique qualities and ease to adapt is a popular and powerful operating system now days. In the chapters to follow we will explore the powers of UNIX in some details.1.10 Answers to the self check questions 1. program 2. False 3. False 4. multitasking 5. multi-user 6. virtual memory 7. True 8. MULTICS 9. True 10. Shell 11. Shell 12. System calls 17
  16. 16. COE Unit 1, Lesson 1 13. telnet 14. system administrator 15. h 16. False1.11 Terminal questions 1. List and expand briefly the components of the UNIX operating system. 2. What are the features of UNIX operating system that are the cause of its popularity amongst the users? 3. Explain briefly the possible modes to log onto a UNIX system1.12 References 1. http://www.uwsg.iu.edu/usail/concepts/unixhx.html18
  17. 17. COE Unit 1, Lesson 2LESSON 2 UNIX COMMAND2. UNIX COMMANDS ......................................................................................................... 21 2.0 OBJECTIVES ............................................................................................................ 21 2.1 INTRODUCTION ........................................................................................................ 21 2.2 THE C OMMANDS CLASS .......................................................................................... 21 2.3 CONNECTING TO UNIX ........................................................................................... 22 2.3.1 telnet command ................................................................................................ 22 2.3.2 rlogin command ................................................................................................ 22 2.4 FILE MANAGEMENT ................................................................................................. 22 2.4.1 mv command..................................................................................................... 23 2.4.2 cp command...................................................................................................... 23 2.4.3 rm command ..................................................................................................... 23 2.5 A COMMUNICATION RELATED COMMAND - FTP ....................................................... 23 2.6 INFORMATION .......................................................................................................... 24 2.6.1 man command .................................................................................................. 24 2.6.2 du – Disk usage ................................................................................................ 25 2.6.3 df – Disk free ..................................................................................................... 25 2.6.4 quota................................................................................................................... 25 2.6.5 who – Finding out who is logged on .............................................................. 25 2.7 PRINTING ................................................................................................................. 26 2.7.1 lpr – Printing ...................................................................................................... 26 2.7.2 lprm – Removing a printing job ...................................................................... 26 2.7.3 lpq – Checking the printing queue ................................................................. 26 2.8 PROCESS CONTROL................................................................................................ 26 2.8.1 ps – Finding the process ................................................................................. 26 2.8.2 & - Running process in background .............................................................. 27 2.8.3 Cntrl-z – Suspending a processes................................................................. 27 2.8.4 Jobs – Finding the process in background................................................... 27 2.8.5 Kill – Killing a process...................................................................................... 27 2.8.6 nice – reducing the priority of process .......................................................... 27 2.9 MISCELLANEOUS COMMANDS ................................................................................. 28
  18. 18. COE Unit 1, Lesson 2 2.9.1 alias / unalias command.................................................................................. 28 2.9.2 cal (calendar) command.................................................................................. 28 2.9.3 clear command ................................................................................................. 28 2.9.4 crontab command............................................................................................. 28 2.9.5 csh command.................................................................................................... 28 2.9.6 history command .............................................................................................. 29 2.9.7 date command .................................................................................................. 29 2.9.8 echo command ................................................................................................. 29 2.9.9 grep command.................................................................................................. 29 2.9.10 unset command ................................................................................................ 29 2.9.11 tar command .................................................................................................... 29 2.9.12 tee command .................................................................................................... 29 2.9.13 touch command ................................................................................................ 29 2.10 SUMMING UP........................................................................................................... 30 2.11 ANSWERS TO THE SELF-CHECK QUESTIONS ........................................................... 30 2.12 TERMINAL QUESTIONS ............................................................................................ 30
  19. 19. COE Unit 1, Lesson 2 2. Unix CommandsUNIX as any other operating system provides a set of commands to its users, usingwhich, the users can perform the tasks they want. There is a huge variety ofcommands that UNIX provides its user. In the present lesson we will discover andread about the usage of many of the commands in UNIX.2.0 Objectives After going through this lesson, you will be able to  Use the UNIX commands to perform tasks  Understand how to send and receive mails on UNIX  Understand the file management basic command  Understand the information and communication system using the UNIX2.1 Introduction UNIX provides a number of commands. For the ease of understanding we can divide these commands into various categories.2.2 The Commands class UNIX commands can be grouped amongst few broader classes:  Starting and Ending These are the commands which are basically used to logon to the UNIX system, or to initiate working on to the UNIX system.  File Management File is the basic data holding entity in the UNIX systems. There is a set of commands that can be used to maintain the file system so as to keep the data stored in the files, secured, updated and maintained.  Communication UNIX provides communications at many levels, including mails, writing messages, exchanging files, etc. 21
  20. 20. COE Unit 1, Lesson 2  Information UNIX provides a number of commands to get information about the system like who are logged in, how much disk space is available, etc.  Printing In UNIX user can give the print command and also can monitor the status of the job or can remove the job if required from the queue.  Job and Process control As there are lots of processes which are going on in a UNIX system, it is sometimes required to get the information related to the user jobs running on the system. For this purpose UNIX provides a set of commands to monitor, kill, prioritize and resuming the jobs. In the present chapter we will look at some of these commands in detail and the other commands will be discussed in the chapters to follow.2.3 Connecting to UNIX Before we learn anything in details the very first thing we will look at is the process that a user has to adopt to start with the UNIX system.2.3.1 telnet command The telnet command is used for logging into a remote system. The telnet command presents the same login and password prompts as done on a local system.2.3.2 rlogin command The rlogin command is used to connect to a remote computer. It is comparatively easier to use then telnet. Here is the syntax of rlogin command: rlogin [-l username] hostname In this the username is taken by default the username of the current user. Hostname is the name of the UNIX machine that is to be logged on.2.4 File Management A file is a basic data storage entity in a UNIX system. There is a set of commands that can be used to maintain this system. We will be having an introductory flavor of these commands in this chapter with the complete discussion being taken up in the chapter on file system. Readers are advised to have a look at the man pages of each of these commands and try to understand what exactly these commands are used for.22
  21. 21. COE Unit 1, Lesson 22.4.1 mv command The mv command moves a file. The command can also be used to rename a file. Here is a simple example of mv command. bash> ls tempPresentation.txt bash> mv tempPresentation.txt finalPresentation.txt bash> ls finalPresentation.txt2.4.2 cp command The cp command copies a file. Here is a simple example of the cp command. bash> ls tempPresentation.txt bash> cp tempPresentation.txt finalPresentation.txt bash> ls tempPresentation.txt finalPresentation.txt2.4.3 rm command The rm command removes a file. Here is an e xample of the rm command. bash> ls tempPresentation.txt finalPresentation.txt bash> rm tempPresentation.txt bash> ls finalPresentation.txt2.5 A communication related command - ftp The ftp (file transfer protocol) command is used for copying files from a remote computer to another computer. While mv and cp works on the same system at a time you might need to get files from across systems at the same time ftp can be used for that. In the example below we can see how ftp can be used to connect to a remote machine. In this example user ‗achint‘ gets file from machine mitserv. 23
  22. 22. COE Unit 1, Lesson 2 bash> ftp mitserv Connected to mitserv Name: achint # User types his login id 31 Please specify the password. Password: # password will not be visible 230 Login successful. Remote system type is UNIX. ftp> get myPresentation.txt # Now you are in ftp. See the prompt 250KB data transfer successful ftp> quit The ftp prompt provides few limited commands as listed below: bash> # You are out of ftp now.  bin – Changes the file transfer type to support the binary image transfer.  get – Used to ‗get‘ the files from remote machine  mget- multiple get commands  ls – Used to list the contents of a directory on a remote machine  cd – Used to change directories on the remote machine  pwd – Used to get the present working directory on remote host  lpwd – Gives the current working directory in local host.2.6 Information The information UNIX commands, regarding other users, disk quota and other things can be retrieved using some of the UNIX commands. In this section we will be discussing about some of these commands.2.6.1 man command UNIX traditionally provides the manual pages (called ‗man‘ pages) for all the built-in commands and for system calls. You can learn a lot by referring to the manual pages for commands. The general syntax of the command is man [-] [-k keywords] topic/command The example below shows a part of the manual page of ‗du‘ command. bash> man du24
  23. 23. COE Unit 1, Lesson 22.6.2 du – Disk usage This command is used to find out how much disk space is been occupied at present by the files and directories of the user.2.6.3 df – Disk free The df command tells how much disk space is left which can be used.2.6.4 quota This command is used for knowing as to how much disk space the files are occupying on the file system.2.6.5 who – Finding out who is logged on The who command displays the information like the usernames, terminal IDs and process IDs of other users and processes running on the computer. General syntax of the command is: who [-q] [am i] Following example shows the output of who command. bash> who singhs :0 May 28 14:05 achint pts/0 May 28 14:06 (lx-ptiwari:0.0) anmol pts/1 May 28 14:12 (lx-ptiwari:0.0)Self-Check Questions1. The commands below are used to connect to the remote computers: i. telnet ii. rlogin iii. rm2. It is not possible to logon to another machine with another username by any means. (True/False)3. If some files are needed to be transferred from a remote location to the current location, we can use the ________________ command for this purpose.4. If a user needs to know the usage of the write command, he can use the ____________ command to know how the command works.5. There is a restriction on the usage of the disk space by a user or a group on the UNIX system and this disk space restriction can be found by using the command _____________.6. To know as to how much total disk space your files and directories have taken, issue __________ command. 25
  24. 24. COE Unit 1, Lesson 27. On a multi-user system, there are more than one people logged onto a machine and this sometimes chokes that machine off. To get in information as to who all are logged onto the machine we can use ______________ command.2.7 Printing UNIX provides commands that for printing documents. Additionally, it is possible to control the printer queue and also to kill the processes if required to cancel the printing job.2.7.1 lpr – Printing This command can be used to print some text in a file. This is used to specify a printer otherwise it issues a print job to the default printer set by the user.2.7.2 lprm – Removing a printing job The lprm command can be used to cancel the print jobs that have been queued or printing. It can be used to cancel printing jobs on the specified printer or to cancel the job on the default printer.2.7.3 lpq – Checking the printing queue This command shows the printer queue status on the named printer. Jobs queued on the default destination will be shown if no printer or class is specified on the command-line.2.8 Process Control When you run a program in UNIX, the program‘s copy starts to run. This running program copy is called a process. The concept of process is fundamental to UNIX OS. So, you should find out and understand details about processes. If you run the same commands twice, each time a new process is started. Every process is identified by a unique process ID and this ID can be used to refer to this process or to perform any further operations on the process, like killing the process. We will have a look at the commands which can be used to control the processes.2.8.1 ps – Finding the process This command is used to list all the processes being run on the machine. bash> ps –ef PID PPID User Process … 233 230 achint ls –l 345 342 anmol ps –ef26
  25. 25. COE Unit 1, Lesson 22.8.2 & - Running process in background By put ‗&‘ at the end of any command, that command runs in the background. Time consuming commands can be put into background so that you can continue working on the same terminal.2.8.3 Cntrl-z – Suspending a processes If some command is by mistake issued and you want to suspend this command and do something else first. Then you can use Cntrl-z to suspend this process and get the CPU free for some other more important work.2.8.4 Jobs – Finding the process in background To find the processes running in the background you can use the jobs command. This is different from the ps command.2.8.5 Kill – Killing a process If some process is running for long time or is producing some unwanted results you can use the ‗kill‘ command to kill the process. The syntax of command is Kill [-signal] [process id] Sometimes a process may still not get killed and you still want to kill it, you can send the -9 signal to kill it.2.8.6 nice – reducing the priority of process This command can be used to reduce the priority of a command and let other commands run earlier than the command. The syntax of command is nice command [command option]Self-Check Questions8. If a print job is fired it is not possible to abort the printing. (True/False)9. To know as to what all are the print processes that are at the printer in queue, we can use ____________ command.10. To print some text in a file, use ______________ command.11. To change the priority of a job we can use the _________ command.12. If some process is fired which is not required at the moment and we need to fire another process, then we suspend the process using _______________ command and continue with the process later on. 27
  26. 26. COE Unit 1, Lesson 213. If it is required to know the processes running on to the system then we will issue ______________ command.2.9 Miscellaneous commands Besides the other commands that we have discussed in this lesson by now, there are numerous other commands in UNIX with lots of options which can be used to perform some amazing tasks. We will be discussing some of these commands with useful and common options that are used. For other options readers can refer the man pages of these commands.2.9.1 alias / unalias command To create or remove an alias for some command these commands are used. The example shows the use bash> alias rm ―rm –i‖ Creates an alias rm which calls rm –i bash> unalias rm Now rm will call rm command2.9.2 cal (calendar) command This command displays the calendar.2.9.3 clear command This command clears the screen2.9.4 crontab command It is sometimes required to run some commands at a specific date and time. For this purpose ‗crontab‘ command can be used. See man crontab for see details. The cron (see man cron) maintains a file which is managed using the crontab command. This file contains the information about the command and the time and date of the execution of the command. Here is an example: bash> crontab –l 0 0 * * 5 echo ―This is a cron‖ | mail john Contents of crontab file.2.9.5 csh command This command is used to run the C shell or to execute a C shell script. The syntax for this command is csh [filename]28
  27. 27. COE Unit 1, Lesson 22.9.6 history command This command is used to list the commands that you have typed so far.2.9.7 date command This command prints the system date and time. The date command has many formatting arguments. See man date for details. bash> date Friday 25 Jan 20082.9.8 echo command This command echoes back string given to it. bash> echo ―My name is achint‖ My name is achint2.9.9 grep command This command is used to search a pattern in a file. We will see more details on grep command in subsequent chapters. Here is a simple example. bash> grep goto file.c /*You should not use goto in c programming */2.9.10 unset command The unset commands removes a shell variable.2.9.11 tar command This command is used to create an archive of files or to extract files from an existing archive. See man tar for details.2.9.12 tee command This command copies text from a pipe into a file. See man tee for details.2.9.13 touch command This command changes the date and time of a file without changing the files content. The touch command creates a file if no t exiting. 29
  28. 28. COE Unit 1, Lesson 2Self-Check Questions14. An ____________ is a short command or word that points at some path, or absolute command name.15. To change the date and time stamp on a file without reading the file __________ command can be used.16. To get the text from a pipe into a file ______ command can be used.2.10 Summing Up UNIX provides a rich set of commands for file management, printing, process control, etc.2.11 Answers to the self-check questions 1. telnet, rlogin. 2. False. 3. ftp 4. man. 5. quota 6. du. 7. Who 8. False 9. lpq 10. enscript 11. nice 12. cntrl-Z 13. ps 14. alias 15. touch 16. tee2.12 Terminal Questions 1. Define and explain the various command classes 2. How is communication handled in UNIX? What is FTP? 3. Describe how File Management is implemented in UNIX 4. List the commands and their usage for various commands used in process control 5. Explain the various print commands in UNIX30
  29. 29. COE Unit 1, Lesson 3LESSON 3 UNIX FILE S YSTEMS3. UNIX FILE SYSTEM ....................................................................................................... 33 3.0 OBJECTIVES ............................................................................................................ 33 3.1 INTRODUCTION ........................................................................................................ 33 3.2 FILES ....................................................................................................................... 33 3.2.1 Filenames .......................................................................................................... 33 3.2.2 Filename Extensions ....................................................................................... 34 3.3 DIRECTORIES .......................................................................................................... 34 3.4 FILE TYPE................................................................................................................ 34 3.4.1 Links ................................................................................................................... 35 3.4.2 Special Files...................................................................................................... 35 3.5 PATH TO A FILE ........................................................................................................ 36 3.5.1 The root directory ............................................................................................. 36 3.5.2 Absolute Path.................................................................................................... 36 3.5.3 Relative Path..................................................................................................... 36 3.6 MANIPULATING FILES .............................................................................................. 36 3.6.1 Moving and Renaming Files and Directories ............................................... 36 3.6.2 Copying files and directories .......................................................................... 36 3.6.3 Removing Files and Directories ..................................................................... 37 3.6.4 Creating a directory.......................................................................................... 37 3.6.5 Listing the files .................................................................................................. 37 3.7 FILE PERMISSIONS .................................................................................................. 38 3.7.1 File Permissions ............................................................................................... 38 3.7.2 Permissions for directories ............................................................................. 39 3.7.3 Changing the permissions on the file ............................................................ 39 3.8 CHANGING FILE OWNER AND GROUP .................................................................... 40 3.9 FILE SEARCH........................................................................................................... 40 3.10 VIEWING BEGINNING AND END OF A FILE................................................................ 40 3.11 ANSWERS TO THE SELF CHECK QUESTIONS ........................................................... 41 3.12 TERMINAL QUESTIONS............................................................................................. 42 3.13 SUGGESTED READING MATERIAL........................................................................... 42
  30. 30. COE Unit 1, Lesson 3 3. UNIX File SystemIn the UNIX operating system the basic storage block is known as a file. This lessonfocuses at understanding the concepts of file manipulation and handling.3.0 Objectives After going through this lesson, you will be able to  Understand the basic concepts of files and directories  Understand the paths and pathnames in UNIX systems  Understand the UNIX file types  Understand the basic UNIX commands related to the file system  Understand the file manipulation and file security3.1 Introduction In a UNIX operating system the basic structure that stores data is known as a file. You can store data of any format in a file. Multiple files can be put together in a directory. Apart from containing files, a directory can contain other directories as well. A directory that is inside another directory is called a subdirectory. A file is analogous to a notebook. A directory is analogous to a bag that contains files.3.2 Files A file contains a sequence of bytes stored on a storage device, such as a disk. On the disk the file is not necessarily stored on a single sector but can be scattered on the disk The OS, keeps track of the information that belongs to a specific sequence of data.3.2.1 Filenames Each file has a name. Any name can be given to a file. The name of a file can be changed anytime. Unlike windows, UNIX file names do not contain spaces. An important thing to remember here is UNIX is case sensitive. Which means ‗A‘ is different than ‗a‘, so one should be very careful while using the cases for separating the file names. So, myfile.txt and myFile.txt are different files. 33
  31. 31. COE Unit 1, Lesson 33.2.2 Filename Extensions UNIX does not enforce any specific extensions on file names. This is unlike Windows where extensions are used to invoke applications directly. In UNIX you can choose any extension for your files. Even multiple extensions are permitted (e.g.,data,tar.gz). Also files need not always have extensions (e.g., myFileOf24Dec2007). Since it is possible to not give extensions, one can create files where extensions are misleading. For example, myProg.db may be a C program while myData.cpp may be containing simple text data. Obviously this is not desirable and one must be careful in putting proper extensions. Though UNIX itself does not enforce any extensions, there are many important utilities/programs that expect a specific file exte nsion. For example, the C compiler expects files with .c or .h extensions.3.3 Directories Files are kept in directories. Directories are the groups of files in some logical structure totally dependent on the application and the user requirements. A directory can contain files and other subdirectories. The figure below shows how the directory myData contains subdirectories which in turn contains the files. myDat a/ Investmen Official ts/ / RBI ICI Sal custo Reports Bonds CI es mers pla n Each directory in UNIX contains two special subdirectories: ./ (The dot directory) This indicates the current directory itself. ../ (The dot dot directory) indicates the parent directory of current directory. bash> pwd Investments Shows current directory as Investments/ bash>cd .. bash>pwd myData Current directory after cd .. is myData/ (the parent)3.4 My name is achint34
  32. 32. COE Unit 1, Lesson 3File Type Regardless of the data contained in a file, UNIX associates a file type for each file. There are 4 file types - ordinary files, directories, links and special files. Ordinary file is any file that you commonly use. These include text files, executable programs, shell scripts, etc. Also, we have already see what are directories. Lets now see links and special files.3.4.1 Links A link is not a file but it is a second name to a file. Sometimes linking files is a good option over copying because once copied, the copies can be changed differently. On the other hand if you create a link then there is actually only one copy of the file. A link is created using the ln command of UNIX. There two types of links, soft link and hard link. See man ln for more details.3.4.2 Special Files UNIX represents even devices with files. These files are special files. For example, the audio output is typically /dev/audio file. What can you do with such a special file? Well, you can write into it or read from a special file and UNIX hides the details on how it is actually working with the device. For example, you can simply cat a music file to /dev/audio and it will be played!Self-Check Questions1. IT is possible to have multiple filename extensions in a file in UNIX. (True/False)2. It is required to have a filename extension in a file in UNIX, which signifies the properties of that file. (True/False)3. Filename work and Work points to the same file in a UNIX file system. (True/False)4. Directories acts as a categorization structure of the data in a UNIX file system. (True/False)5. __________________ is a directory under the parent directory, which can be used for the categorization of data further down the hierarchical file structure.6. Which is not a UNIX file type? a) Links b) Symbolic Links c) Program files d) Directories7. A ______________ (soft/hard) is only a te xt file that points to some other file somewhere in the file system and does not contains the data. 35
  33. 33. COE Unit 1, Lesson 33.5 Path to a file3.5.1 The root directory UNIX OS treats the directory / as the root directory. The root directory is the ultimate parent of all other directories on a UNIX system.3.5.2 Absolute Path Every file on a system has a path that starts from the root. For example, bash> pwd /dtu/IT_Courses/IT_101/schedules.txt This is the absolute path to the ―schedules‖ file. The pwd command always lists the absolute path.3.5.3 Relative Path When in a directory, if you know the relative position of a file, you need not access that file using absolute path. You can simply use the relative path to the desired file as well. This is shown in an example below: You can also access files using relative paths. For example, bash> pwd This is the relative path of /dtu/It_Courses/IT_999 ―schedules.txt‖ with respect to ―/dtu/It_Courses/IT_999‖ bash> ls ../IT-102/schedule.txt3.6 Manipulating Files The file manipulation operations are – file deletion, file renaming and moving files from one location to another.3.6.1 Moving and Renaming Files and Directories The mv command of UNIX moves files and directories to specified locations. bash> mv –i data data.old Moves data to data.old bash> mv –i data new bash> mv –i oldDir newDir Moves data into new/ directory Moves oldDir to newDir3.6.2 Copying files and directories36
  34. 34. COE Unit 1, Lesson 3 The cp command of UNIX copies files and directories.. bash> cp old new Copies file old to new. Overwrites new if exists. bash> cp –R /home/joe/bread /home/jam/food Copies all files and subdirectories to the target directory3.6.3 Removing Files and Directories Often you want to files or some directory (including its contents). For example you may be cleaning your system. The rm command deletes files and directories. bash> rm file.txt my.txt Removes specified files. -f option indicates that rm will not give bash> rm –f file.txt error even if file given to be deleted does not exist. bash> rm –r directory1 -r option indicates delete all subdirectories as well. Be careful with rm command. A file or directory once deleted cannot e undeleted in UNIX. There is no such thing as trash can in UNIX. It is advisable to use the –i option of rm command all the time. See man rm for details. If a directory is empty, then it can be deleted using rmdir command. See man rmdir for details.3.6.4 Creating a directory The mkdir command creates a new directory. bash> mkdir project Will create directory project/ bash> mkdir /home/anmol/data bash> mkdir ../../myDir Absolute path can be given to create a dir Relative path can be given3.6.5 Listing the files The ls command of UNIX lists files and directories in the current directory. lt has a large number of other options (see man ls). 37
  35. 35. COE Unit 1, Lesson 3 bash> ls -l achint is the file owner. drwxr--r-- 1 achint editors 4096 drafts editors is the group. Size is -rw-r--r-- 1 achint editors 30405 edition-32 8460 bytes -r-xr-xr-x 1 achint editors 8460 final_draft This field explains file permissions and file type the fields are explained in table belowSelf-Check Questions8. The __________________ is the parent directory of all types of directories in the UNIX file system.9. The name of file starting from the root directory is called the _____________ pathname of the file.10. The relative pathname of a file is the name of the file with respect to the parent directory. (True/False)11. Pick the odd one out Following operations can be performed on the file system a) Building b) Listing c) Renaming filenames d) Copying12. On using the ‗mv‘ command from one file to an existing file it ___________ (appends/overwrites) the contents of the moved file onto existing file.13. To copy one directory to the other it is mandatory to use the option _______ with the command ‗cp‘.14. Command ‗rmdir‘ can be used to delete the complete hierarchical directory structure. (True/False)3.7 File Permissions UNIX enforces permissions for files and directories. If you are the owner of a file, you can put permissions whether the file should be readable by others or not, and so on. Lets see more details about file permissions.3.7.1 File Permissions The user of the UNIX file system can belong to three classes:  The owner of the file  The group which the file belongs to  Other users38
  36. 36. COE Unit 1, Lesson 3 bash> ls -l drwxr--r-- 1 achint editors 4096 drafts -rw-r--r-- 1 achint editors 30405 edition-32 These 3 indicate -rwxr-xr-- 1 achint editors 8460 final_draft group people can read/execute but cannot write into -rwxr-xr-- this file These 3 indicates First letter: others can only - means read this file. ordinary file d means These 3 letters indicates file directory readable, writable l means its a and can be executed link by the owner.3.7.2 Permissions for directories For the directories read permissions enables the user to list the contents of the directory; Write permissions allows the users to create a file or a directory inside that directory and execute permissions allows to change the present working directory to that directory.3.7.3 Changing the permissions on the file The chmod command changes the permissions for a file and directory. See man chmod for details. There are several ways to change the permissions of a file. Here are few examples: bash>chmod ug+r w sample Permits user and group to read and write bash> ls -ld sample in file drw-rw---- 2 achint editor 96 Dec 8 12:53 sample bash> chmod a-rwx sample Removes permissions for all bash> ls -l sample ---------- 2 amol editor 96 Dec 8 12:53 sample There is another form in which the permissions can be directly set for the files by using an octal code. With three-digit octal notation, each numeral represents a different component of the permission set: user class, group class, and "others" class respectively. For example, the number 764 in octal can be represented as following in binary 111110100. 39
  37. 37. COE Unit 1, Lesson 3  The first octal digit when converted to binary represents the permissions for owner (7 in octal is 111 in binary which implies rwx for owner).  The next octal digit when converted to binary represents the permissions for the group (6 in octal is 110 in binary which implies rw- for group).  The last octal digit when converted to binary represents the permissions for the others (4 in octal is 100 in binary which implies r-- for other).3.8 Changing File Owner and Group The chown command changes the owner of a file. See man chown for details. The chgrp command changes the group of a file. See man chgrp for details.3.9 File Search The find command helps in locating files and directories. This is a powerful command and has lots of options. See man find for details. Here is the syntax of the find command. find search_directory –name file_name [-print] The find command searches through the contents of one or more directories including all of their subdirectories. bash> find / -name schedule -print /dtu/IT_courses/IT_101/schedule Finds all the files in ‗/‘ named /dtu/IT_courses/IT_102/schedule schedule Another example in which same file name is searched in two directories: bash> find . –type d –name abc -print Finds ‗directory‘ abc and not file in the present directory.3.10 Viewing Beginning and End of a file UNIX provides commands using which it is possible to display the contents of the start or end of the file. These are head and tail commands. head – Start of the file tail – end of the file40
  38. 38. COE Unit 1, Lesson 3 Example usage bash> head –n 10 file Shows the 10 starting lines of ‗file‘Self-Check Questions15. Pick the odd one out The users in a UNIX file system can be categorized as: a) Owners b) Group c) Friends d) Other users16. To change the file permissions from one set to another, the command ___________ can be used.17. __________________ command is used to change the owner and the group of the file.18. The _______ command lets you search for files and directories.19. The _______ command will be useful to show the last few lines of a file.3.11 Answers to the self check questions 1. True 2. False 3. False 4. True 5. Subdirectory 6. Program files. 7. Soft link 8. Root. 9. Absolute path.. 10. True 11. Building 12. overwrites. 13. –r 14. False 15. Friends 16. Chmod 17. Chown, chgrp 18. Find 19. tail 41
  39. 39. COE Unit 1, Lesson 33.12 Terminal questions 1. Write a detailed note about the hierarchical file structure. 2. Explain briefly the manipulating operations possible on the file structure 3. Write a brief note on the permissions on the files and directories in UNIX. Also, explain how we can change permissions of the files in UNIX using the chmod command. Use some relevant examples to explain the concepts. 4. Explain the UNIX system file types, also explain the salient features of each file type3.13 Suggested Reading Material 1. Unix Programming Environment, by Kernighan and Pike. 2. Design of Unix Operating System, by Maurice J. Bach42
  40. 40. COE Unit 1, Lesson 4LESSON 4 T HE VI T EXT EDITOR4. THE VI TEXT EDITOR.................................................................................................... 45 4.0 OBJECTIVES ............................................................................................................ 45 4.1 INTRODUCTION ........................................................................................................ 45 4.2 FILES CONTAIN STREAM OF CHARACTERS .............................................................. 45 4.3 HOW VI HANDLES THE FILES ................................................................................. 46 4.4 INVOKING VI ............................................................................................................. 46 4.5 MODES OF VI ........................................................................................................... 46 4.5.1 Command mode ............................................................................................... 46 4.5.2 Edit mode........................................................................................................... 46 4.5.3 Switching between command mode and edit mode................................... 47 4.6 POSITIONING TE XT ON THE SCREEN ...................................................................... 47 4.6.1 Scrolling and moving the Screen ................................................................... 47 4.6.2 The GOTO Command ..................................................................................... 48 4.6.3 Searching........................................................................................................... 48 4.7 POSITIONING THE C URSOR : H, L, J, K COMMANDS................................................. 48 4.8 EDITING USING SCOPES .......................................................................................... 49 4.8.1 Delete Text (d, D) ............................................................................................. 50 4.8.2 Change Text (c, C) ........................................................................................... 50 4.8.3 Replace Command (r, R) ................................................................................ 50 4.8.4 Erase Command (x, X) .................................................................................... 51 4.8.5 Undo Command (u, U) .................................................................................... 51 4.9 TE XT INSERTION ...................................................................................................... 51 4.9.1 Append Command (a, A) ................................................................................ 51 4.9.2 Insert Command (i, I) ....................................................................................... 52 4.9.3 Open Command (o, O) .................................................................................... 52 4.9.4 Read Command (:r) ......................................................................................... 52 4.10 GLOBAL SEARCH AND REPLACE FOR TEXT ............................................................ 52 4.11 REARRANGING AND DUPLICATING TEXT................................................................. 53 4.11.1 Copying Text and Moving the Copy .............................................................. 53 4.11.2 Deleting Text and Moving It ............................................................................ 54
  41. 41. COE Unit 1, Lesson 4 4.12 NAMED BUFFERS .................................................................................................... 54 4.12.1 Using the named buffers ................................................................................. 55 4.13 MISCELLANEOUS INFORMATION .............................................................................. 56 4.13.1 Creating Line Numbers ................................................................................... 56 4.13.2 Lines and Sentences in VI .............................................................................. 56 4.13.3 Joining Lines ..................................................................................................... 57 4.13.4 Repeating a Command ................................................................................... 57 4.13.5 Editing Multiple Files Using vi......................................................................... 57 4.13.6 Mark Command ................................................................................................ 58 4.14 SAVING OR STORING A FILE.................................................................................... 58 4.14.1 Writing to the file ............................................................................................... 59 4.14.2 Exiting the vi editor ........................................................................................... 59 4.15 SUMMING UP........................................................................................................... 60 4.16 ANSWERS TO THE SELF-CHECK QUESTIONS ........................................................... 60 4.17 TERMINAL QUESTIONS ............................................................................................ 61
  42. 42. COE Unit 1, Lesson 4 4. The VI Text EditorWhen you write programs, scripts or modify data, write mails, etc., you will need touse text editor. This lesson focuses on the VI text editor; one of the most commonlyused text editors in UNIX systems.4.0 Objectives After going through this lesson, you will be able to  Understand how to open and edit files using vi  Understand various text insertion and deletion methods in vi  Understand the basic structure of vi text editor  Understand the commands to edit text using vi and scopes  Understand miscellaneous other features of vi4.1 Introduction vi is a visual, non-graphical and interactive text editor which allows a user to create, modify, and store files on the computer. Note that in this chapter, the cursor is shown by putting an underscore for a character. For example: The cursor is at the letter ‗n‘ in the following line. This is a line. Theres an editor out there that programmers have been using to edit their programs for the last 24 years. Its called vi (say vee-eye) and it is it is quite powerful. http://www.websiterepairguy.com/articles/vi/12_learn_vi.html4.2 Files contain stream of characters When you type characters or numbers, etc. each key goes as an ASCII character. For example, ‗a‘ gets recorded as ASCII 97. When you write lines like these This is line 1 This is line 2 These lines are stored as a stream of characters like ―This is line 1 nThis is line 2‖. Here the n is a special character which signifies a new line. 45
  43. 43. COE Unit 1, Lesson 44.3 How Vi Handles The Files When you open a file in vi, the file contents are read into a buffer. All text editing jobs are done in memory as the buffer. The file on the disk is not updated unless vi is explicitly asked to save the changes. This gives an option to change the content of the buffer until you are not satisfied without changing the file on the disk.4.4 Invoking vi The vi editor can be invoked using the following command $ vi demo.txt The figure below shows how the file looks when opened in vi. The cursor ~ ~ Tile(~) in vi represents an ~ empty line. ~ .4.5 Modes of vi . File information ―myfile‖ [new vi has two modes in which you will work. file]4.5.1 Command mode The command mode is the default mode. All vi commands work only in the command mode. In the command mode you cannot write text. You can only move around in the text, delete text, modify existing text, search for text, etc.4.5.2 Edit mode In edit mode you can add new text in vi. In edit mode you cannot use any commands to search or navigate in the text.46
  44. 44. COE Unit 1, Lesson 44.5.3 Switching between command mode and edit mode When in command mode, few commands take you to edit mode. For example, in the command mode, if you press i, you will get to the edit mode and can add text. When in the edit mode, you can stop editing further and go to the command mode by pressing the <Esc> key.4.6 Positioning Text on the Screen This is a You are in command line mode and cursor is at ‘a’. press ‗i‘ This is a Cursor is at same position line but edit mode has started This is da now press ‗d‘ Cursor is at letter ‗a‘ and line Press letter ‗d‘ is added. ‗esc‘ This is provides several ways you are in text you want to edit in a file. vi da Now to reach the line command mode4.6.1 Scrolling and moving the Screen By scrolling the screen we can reach the text desired. The table below explains how one can scroll the screen. Command Resulting Action Cntrl+u Moves window upwards one complete screen Cntrl+d Moves window downwards one complete screen H Takes cursor to the top of the screen L Takes the cursor to the bottom of the screen M Takes the cursor to the middle of the screen All these commands work only in the command mode. 47
  45. 45. COE Unit 1, Lesson 44.6.2 The GOTO Command Sometimes you already know the line number where you want to reach. You can use the GOTO in such cases. The table below explains the command and the resulting action. Command Resulting Action G Moves cursor to the last line <N>G Moves the cursor to the Nth line Like 33G :<N> Moves the cursor to the Nth line Like :654.6.3 Searching It is also possible to search for a pattern and by this the screen will be moved to the occurrences of the desired pattern. Here are the commands that work for search in vi.. Command Resulting Action ‗/pattern‘ Searches the pattern forward from current cursor position ‗?pattern‘ Searches the pattern backward from current cursor position :set ic This makes the subsequent searches case insensitive (ic in set ic stands for ignore case) :set noic This makes the subsequent searches case sensitive Once you start a search you can repeat the search in a simple way. On keying in ‗n‘ vi goes to the next instance of pattern in the file and using ‗N‘ it searches in opposite direction.4.7 Positioning the Cursor : h, l, j, k commands This section explains finer control of the cursor. You can move the cursor by use of "arrow" keys. You can also use the "direction" keys "h" (move left by one character), "j" (move down to next lined), "k" (move up to previous line), and "l" (move right by one character). The "RETURN" key is similar to the "j" key in that it moves the cursor down one line. However, the "RETURN" key always positions the cursor at the beginning of the next line; whereas, the "j" key moves the cursor straight down from its present position, which may be the middle of a line. Moving several spaces may be accomplished by repeatedly pressing the "RETURN", direction48
  46. 46. COE Unit 1, Lesson 4 or arrow key; such as, "k" "k" "k" to move upward 3 lines. You can also precede any of these keys with a number and achieve the same results, "3k".Self-Check Questions1. If in a file cursor is resting at the 34 line and it is desired to be placed onto the 74 line then the command that is to be issued is _____________G.2. On searching with ―?‖ and ―/‖, the search respectively will be done ______________ and ____________________. (backwards/forward).3. To get the file statistics using the VI editor the command required to be issued is ___________.4. On keying in ―N‖ while searching for a pattern using ―?‖ the cursor will reach the next instance of the pattern ________________. (backward/forward)5. To move to the 25 word in the line while the cursor is on 18 line the command that can be issued is ___________.6. To move to the beginning of the line on which the cursor is residing in a text file the command that can be issued is __________.7. The vi editor sets or creates a temporary buffer area while editing a file which is stored on the disk and is used later on for the reference purpose by the editor. (True/False)4.8 Editing using scopes vi commands have scope built into them. For example, when you say ‗dd‘ then first ‗d‘ indicates the delete operations and the second ‗d‘ tells it to apply the command on a line. Similarly, ‗yy‘ yanks a line. But the commands like ‗d‘ and ‗y‘ can be given a scope and VI commands also have upper case versions. Scope Text Unit Encompassed 0 Beginning of line $ End of line W w Word right B b Word left E e End of word right With the scopes we can use the operators to get more powerful outcomes. We can further do editing very much locally using the combination of the operators and scopes. In this section we will discuss this combination. 49
  47. 47. COE Unit 1, Lesson 44.8.1 Delete Text (d, D) The delete command is used in command mode to remove portions of text from the file being edited. The scope must be specified after the delete operator. Some of the most common scopes used with the delete operator shown in the next table. Delete Resulting Action operator and scope dw Delete word forward D( Delete complete sentence backward d) Delete complete sentence forward dG Delete from current line to end of file dL Delete from current line to end of screen d/^xyz Delete from current line to first occurrence of pattern dtx Delete from current place to first occurrence of ‗x‘ NOTE: The same scope prefixes can be used with all the scoped text editing commands so we will not discuss them with any further commands b ut different scopes or operators, if any will be discussed. NOTE: It is important to remember that the current cursor position serves as the starting point for the scope. This means if you do scoped deletion, it will happen starting from the current point. For example, typing "2dd" will delete two consecutive lines beginning with the current line.4.8.2 Change Text (c, C) You can use the change command to change the text in a line. Scopes are applied in the same manner as they are used with the delete command. On issuing the change text command, vi gets into the edit mode and after the text insertion on issuing the <ESC> key it returns to the command mode. The example shows how change command can be used. This is the line to watch Cursor is positioned at‗t‘ On issuing the command ‗2cw‘ or change two words and keying in ―new line‖ Text inserted in place of4.8.3 Replace Command (r, R) This is new line to watch two words The replace command is used to replace portions of text on the screen. The table shows the two variants of the replace command and their usage for replacing text.50
  48. 48. COE Unit 1, Lesson 4 Replace Text replacing action command r Used to replace a single character at a time R Used to replace as many characters as there are keystroke until user issue <ESC> This is the line to watch out for. Cursor positioned at ‗l‘ On issuing ‗r‘ command and typing ‗m‘ ‘l‘ is replaced by ‗m‘ This is the mine to watch out for.4.8.4 Erase issuing ‗R‘ command, On Command (x, X) keying in ―kite‖ and <ESC> Complete word is The erase command removes a character. replaced This is the kite to watch out for. Erase Erase Action Command x Erase character on which cursor is placed X Erase character left to cursor4.8.5 Undo Command (u, U) Undo command reverses the effect of the editing operations done on a file. ‗u‘ reverses the effect of last editing command whereas ‗U‘ reverses the effect of all the editing operations on the file since last save.4.9 Text Insertion vi editor provides several ways to insert the text in the file. We will be discussing each of these methods in some detail but it is advisable for a newly inducted candidate to take up one approach and use that to insert the text.4.9.1 Append Command (a, A) It is used to add to the existing text. It has two forms ‗a‘ and ‗A‘. These two forms are explained in the figure below. The student laughed. On issuing ‗a‘ command and typing ‗s‘ and <ESC> The students laughed. Text appended after the cursor 51 The students laughed. Aloud.
  49. 49. COE Unit 1, Lesson 44.9.2 Insert Command (i, I) This command is used to insert the text into a text file. This command has two forms ‗i‘ and ‗I‘. In the figure below it is explained how to use this command. The student laughed. On issuing ‗i‘ command and typing ‗new ‘and <ESC> The new student laughed. Text inserted before the cursor On issuing ‗I‘ command and typing appended at end of line. Text ‗Again‘and<ESC> Text appended in the Again The student laughed. beginning of line.4.9.3 Open Command (o, O) Open command opens a new line to add text. This has two forms ‗o‘ and ‗O‘, in the figure below the usage is explained. The student laughed. On issuing ‘O’ command and typing ‘A new line is added’ and ESC> A new line is added The student laughed. Text inserted above the current line On issuing ‘o’ command and typing ‘Another line ’ and <ESC> A new line added The student laughed. Another line Text appended in the beginning of the line.4.9.4 Read Command (:r) The read command is allows the user to copy of another file into the current file. While in command mode and with the cursor on the line above where you want the special file read in, type: :r <File> Reads the file specified at cursor location in the current file4.10 Global Search and Replace for text52

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