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Linux and shell programming, MCA, Jawaharlal Nehru Technological University
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MCA II-I Sem Th 4 (9F00303) LINUX PROGRAMMING UNIT I Linux Utilities-File handling utilities, Security by file permissions, Process utilities, Disk utilities, Networking commands, Filters, Text processing utilities and Backup utilities, sed – scripts, operation, addresses, commands, applications, awk – execution, fields and records, scripts, operation, patterns, actions, functions, using system commands in awk. UNIT II Working with the Bourne again shell(bash): Introduction, shell responsibilities, pipes and input Redirection, output redirection, here documents, running a shell script, the shell as a programming language, shell meta characters, file name substitution, shell variables, command substitution, shell commands, the environment, quoting, test command, control structures, arithmetic in shell, shell script examples, interrupt processing, functions, debugging shell scripts. Linux Files: File Concept, File System Structure,Inodes, File types, The standard I/O (fopen, fclose, fflush, fseek, fgetc, getc, getchar, fputc, putc, putchar, fgets, gets etc.), formatted I/O, stream errors, kernel support for files, System calls, library functions, file descriptors, low level file access - usage of open, creat, read, write, close, lseek, stat family, umask, dup, dup2, fcntl, file and record locking. file and directory management - chmod, chown, links(soft links & hard links - unlink, link, symlink), mkdir, rmdir, chdir, getcwd, Scanning Directories-opendir, readdir, closedir,rewinddir, seekdir, telldir functions. UNIT III Linux Process – Process concept, Kernel support for process, process attributes, process hierarchy,process states,process composition, process control - process creation, waiting for a process, process termination, zombie process,orphan process, system call interface for process management-fork, vfork, exit, wait, waitpid, exec family, system.Signals Interprocess Communication : Introduction to IPC, IPC between processes on a single computer system, IPC between processes on different systems,pipes, FIFOs, Introduction to three types of IPC(Linux)-message queues, semaphores and shared memory. Message Queues. UNI-IV Semaphores-Kernel support for semaphores, Linux APIs for semaphores, file locking with semaphores.
Introduction to Linux Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of Linux is the Linux kernel, an operating system kernel first released 5 October 1991 by Linus Torvalds. Linux was originally developed as a free operating system for Intel x86-based personal computers. It has since been ported to more computer hardware platforms than any other operating system. It is a leading operating system on servers and other big iron systems such as mainframe computers and supercomputers more than 90% of today's 500 fastest supercomputers run some variant of Linux, including the 10 fastest. Linux also runs on embedded systems (devices where the operating system is typically built into the firmware and highly tailored to the system) such as mobile phones, tablet computers, network routers, televisions and video game consoles; the Android system in wide use on mobile devices is built on the Linux kernel. A distribution oriented toward desktop use will typically include the X Window System and an accompanying desktop environment such as GNOME or KDE Plasma. Some such distributions may include a less resource intensive desktop such as LXDE or Xfce for use on older or less powerful computers. A distribution intended to run as a server may omit all graphical environments from the standard install and instead include other software such as the Apache HTTP Server and an SSH server such as OpenSSH. Because Linux is freely redistributable, anyone may create a distribution for any intended use. Applications commonly used with desktop Linux systems include the Mozilla Firefox web browser, the LibreOffice office application suite, and the GIMP image editor.Since the main supporting user space system tools and libraries originated in the GNU Project, initiated in 1983 by Richard Stallman, the Free Software Foundation prefers the name GNU/Linux. History of Unix The Unix operating system was conceived and implemented in 1969 at AT&T's Bell Laboratories in the United States by Ken Thompson, Dennis Ritchie, Douglas McIlroy, and Joe Ossanna. It was first released in 1971 and was initially entirely written in assembly language, a common practice at the time. Later, in a key pioneering approach in 1973, Unix was re-written in the programming language C by Dennis Ritchie (with exceptions to the kernel and I/O). The availability of an operating system written in a high-level language allowed easier portability to different computer platforms. Today, Linux systems are used in every domain, from embedded systems to supercomputers, and have secured a place in server installations often using the popular LAMP application stack. Use of Linux distributions in home and enterprise desktops has been growing. They have also gained popularity with various local and national governments. The federal government of Brazil is well known for its support for Linux. News of the Russian
military creating its own Linux distribution has also surfaced, and has come to fruition as the G.H.ost Project. The Indian state of Kerala has gone to the extent of mandating that all state high schools run Linux on their computers. Design A Linux-based system is a modular Unix-like operating system. It derives much of its basic design from principles established in Unix during the 1970s and 1980s. Such a system uses a monolithic kernel, the Linux kernel, which handles process control, networking, and peripheral and file system access. Device drivers are either integrated directly with the kernel or added as modules loaded while the system is running. Separate projects that interface with the kernel provide much of the system's higher- level functionality. The GNU userland is an important part of most Linux-based systems, providing the most common implementation of the C library, a popular shell, and many of the common Unix tools which carry out many basic operating system tasks. The graphical user interface (or GUI) used by most Linux systems is built on top of an implementation of the X Window System. Programming on Linux Most Linux distributions support dozens of programming languages. The original development tools used for building both Linux applications and operating system programs are found within the GNU toolchain, which includes the GNU Compiler Collection (GCC) and the GNU build system. Amongst others, GCC provides compilers for Ada, C, C++, Java, and Fortran. First released in 2003, the Low Level Virtual Machine project provides an alternative open-source compiler for many languages. Proprietary compilers for Linux include the Intel C++ Compiler, Sun Studio, and IBM XL C/C++ Compiler. BASIC in the form of Visual Basic is supported in such forms as Gambas, FreeBASIC, and XBasic. Most distributions also include support for PHP, Perl, Ruby, Python and other dynamic languages. While not as common, Linux also supports C# (via Mono), Vala, and Scheme. A number of Java Virtual Machines and development kits run on Linux, including the original Sun Microsystems JVM (HotSpot), and IBM's J2SE RE, as well as many open- source projects like Kaffe and JikesRVM. Linux Advantages
Linux is just a kernel. All Linux distributions includes GUI system + GNU utilities (such as cp, mv, ls,date, bash etc) + installation & management tools + GNU c/c++ Compilers
End User Perspective The differences are not that big for the average end user. They will use the same shell (e.g. bash or ksh) and other development tools such as Perl or Eclipse development tool. System Administrator Perspective Again, the differences are not that big for the system administrator. However, you may notice various differences while performing the following operations:
out and purchase a US Robotics external modem because that was the one modem I knew would work. This is not so much the case now. You can grab a PC (or laptop) and most likely get one or more Linux distributions to install and work nearly 100 percent. But there are still some exceptions. For instance, hibernate/suspend remains a problem with many laptops, although it has come a long way. With Windows, you know that most every piece of hardware will work with the operating system. Of course, there are times (and I have experienced this over and over) when you will wind up spending much of the day searching for the correct drivers for that piece of hardware you no longer have the install disk for. But you can go out and buy that 10-cent Ethernet card and know it’ll work on your machine (so long as you have, or can find, the drivers). You also can rest assured that when you purchase that insanely powerful graphics card, you will probably be able to take full advantage of its power. #5: Command line vs. no command line No matter how far the Linux operating system has come and how amazing the desktop environment becomes, the command line will always be an invaluable tool for administration purposes. Nothing will ever replace my favorite text-based editor, ssh, and any given command-line tool. I can’t imagine administering a Linux machine without the command line. But for the end user — not so much. You could use a Linux machine for years and never touch the command line. Same with Windows. You can still use the command line with Windows, but not nearly to the extent as with Linux. And Microsoft tends to obfuscate the command prompt from users. Without going to Run and entering cmd (or command, or whichever it is these days), the user won’t even know the command-line tool exists. And if a user does get the Windows command line up and running, how useful is it really? #6: Centralized vs. noncentralized application installation The heading for this point might have thrown you for a loop. But let’s think about this for a second. With Linux you have (with nearly every distribution) a centralized location where you can search for, add, or remove software. I’m talking about package management systems, such as Synaptic. With Synaptic, you can open up one tool, search for an application (or group of applications), and install that application without having to do any Web searching (or purchasing). Windows has nothing like this. With Windows, you must know where to find the software you want to install, download the software (or put the CD into your machine), and run setup.exe or install.exe with a simple double-click. For many years, it was thought that installing applications on Windows was far easier than on Linux. And for many years, that thought was right on target. Not so much now. Installation under Linux is simple, painless, and centralized. #7: Flexibility vs. rigidity I always compare Linux (especially the desktop) and Windows to a room where the floor and ceiling are either movable or not. With Linux, you have a room where the floor and ceiling can be raised or lowered, at will, as high or low as you want to make them. With Windows, that floor and ceiling are immovable. You can’t go further than Microsoft has deemed it necessary to go. Take, for instance, the desktop. Unless you are willing to pay for and install a third- party application that can alter the desktop appearance, with Windows you are stuck with
what Microsoft has declared is the ideal desktop for you. With Linux, you can pretty much make your desktop look and feel exactly how you want/need. You can have as much or as little on your desktop as you want. From simple flat Fluxbox to a full-blown 3D Compiz experience, the Linux desktop is as flexible an environment as there is on a computer. #8: Fanboys vs. corporate types I wanted to add this because even though Linux has reached well beyond its school- project roots, Linux users tend to be soapbox-dwelling fanatics who are quick to spout off about why you should be choosing Linux over Windows. I am guilty of this on a daily basis (I try hard to recruit new fanboys/girls), and it’s a badge I wear proudly. Of course, this is seen as less than professional by some. After all, why would something worthy of a corporate environment have or need cheerleaders? Shouldn’t the software sell itself? Because of the open source nature of Linux, it has to make do without the help of the marketing budgets and deep pockets of Microsoft. With that comes the need for fans to help spread the word. And word of mouth is the best friend of Linux. Some see the fanaticism as the same college-level hoorah that keeps Linux in the basements for LUG meetings and science projects. But I beg to differ. Another company, thanks to the phenomenon of a simple music player and phone, has fallen into the same fanboy fanaticism, and yet that company’s image has not been besmirched because of that fanaticism. Windows does not have these same fans. Instead, Windows has a league of paper- certified administrators who believe the hype when they hear the misrepresented market share numbers reassuring them they will be employable until the end of time. #9: Automated vs. nonautomated removable media I remember the days of old when you had to mount your floppy to use it and unmount it to remove it. Well, those times are drawing to a close — but not completely. One issue that plagues new Linux users is how removable media is used. The idea of having to manually “mount” a CD drive to access the contents of a CD is completely foreign to new users. There is a reason this is the way it is. Because Linux has always been a multiuser platform, it was thought that forcing a user to mount a media to use it would keep the user’s files from being overwritten by another user. Think about it: On a multiuser system, if everyone had instant access to a disk that had been inserted, what would stop them from deleting or overwriting a file you had just added to the media? Things have now evolved to the point where Linux subsystems are set up so that you can use a removable device in the same way you use them in Windows. But it’s not the norm. And besides, who doesn’t want to manually edit the /etc/fstab fle? #10: Multilayered run levels vs. a single-layered run level I couldn’t figure out how best to title this point, so I went with a description. What I’m talking about is Linux’ inherent ability to stop at different run levels. With this, you can work from either the command line (run level 3) or the GUI (run level 5). This can really save your socks when X Windows is fubared and you need to figure out the problem. You can do this by booting into run level 3, logging in as root, and finding/fixing the problem. With Windows, you’re lucky to get to a command line via safe mode — and then you may or may not have the tools you need to fix the problem. In Linux, even in run level 3, you can still get and install a tool to help you out (hello apt-get install APPLICATION via the command line). Having different run levels is helpful in another way. Say the machine in question is a
The above cat command will concatenate the two files (file1.txt and file2.txt) and it will display the output in the screen. Some times the output may not fit the monitor screen. In such situation you can print those files in a new file or display the file using less command. cat file1.txt file2.txt | less
cd [directory | ~ | ./ | ../ | - ] OPTIONS:
7373080 child.gif 7373081 email.gif 7373076 indigo.gif The above command displays filename with inode value. ln Command: ln command is used to create link to a file (or) directory. It helps to provide soft link for desired files. Inode will be different for source and destination. SYNTAX: The Syntax is ln [options] existingfile(or directory)name newfile(or directory)name OPTIONS:
mkdir - m 666 test The above command is used to create the directory 'test' and set the read and write permission. rmdir Command: rmdir command is used to delete/remove a directory and its subdirectories. SYNTAX: The Syntax is rmdir [options..] Directory OPTIONS:
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