(ebook) Linux Shell Scripting Tutorial.pdf

Linux Shell Scripting Tutorial

Linux Shell Scripting Tutorial Ver. 1.0

Written by Vivek G Gite

I N D E X

Introduction

Kernel

Shell

How to use Shell

Common Linux Command Introduction

Process

Why Process required

Linux commands related with process

Redirection of Standard output/input

Redirectors

Pipes

Filters

Shell Programming

Variables in Linux

How to define User defined variables

Rules for Naming variable name

How to print or access value of UDV (User defined variables)

How to write shell script

How to Run Shell Scripts

Quotes in Shell Scripts

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Linux Shell Scripting Tutorial

Shell Arithmetic

Command Line Processing (Command Line Arguments)

Why Command Line arguments required

Exit Status

Programming Commands

echo command

Filename Shorthand or meta Characters (i.e. wild cards)

Decision making in shell script ( i.e. if command)

test command or [ expr ]

Loop in shell scripts

The case Statement

The read Statement

More Advanced Shell Script Commands

/dev/null - Use to send unwanted output of program

Local and Global Shell variable (export command)

Conditional execution i.e. && and ||

I/O Redirection and file descriptors

Functions

User Interface and dialog utility

trap command

getopts command

More examples of Shell Script (Exercise for You :-)

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Linux Shell Script Tutorial

Introduction

This tutorial is designed for beginners only and This tutorial explains the basics of

shell programming by showing some examples of shell programs. Its not help or

manual for the shell. While reading this tutorial you can find manual quite useful (

type man bash at $ prompt to see manual pages). Manual contains all necessary

information you need, but it won't have that much examples, which makes idea

more clear. For that reason, this tutorial contains examples rather than all the

features of shell. I assumes you have at least working knowledge of Linux i.e. basic

commands like how to create, copy, remove files/directories etc or how to use

editor like vi or mcedit and login to your system. Before Starting Linux Shell Script

Programming you must know

Kernel

Shell

Process

Redirectors, Pipes, Filters etc.

What's Kernel

Kernel is hart of Linux O/S. It manages resource of Linux O/S. Resources means

facilities available in Linux. For eg. Facility to store data, print data on printer,

memory, file management etc . Kernel decides who will use this resource, for how

long and when. It runs your programs (or set up to execute binary files) It's

Memory resident portion of Linux. It performance following task :-

I/O management

Process management

Device management

File management

Memory management

What's Linux Shell

Computer understand the language of 0's and 1's called binary language, In early

days of computing, instruction are provided using binary language, which is difficult

for all of us, to read and write. So in O/s there is special program called Shell. Shell

accepts your instruction or commands in English and translate it into computers

native binary language.

This is what Shell Does for US

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Linux Shell Script Tutorial

You type Your command and shell convert it as

It's environment provided for user interaction. Shell is an command language

interpreter that executes commands read from the standard input device

(keyboard) or from a file. Linux may use one of the following most popular shells

(In MS-DOS, Shell name is COMMAND.COM which is also used for same purpose,

but it's not as powerful as our Linux Shells are!)

Shell Name

Developed by

Where

Remark

BASH ( Bourne-Again

SHell )

Brian Fox and Chet

Ramey

Free Software

Foundation

Most common shell in

Linux. It's Freeware

shell.

CSH (C SHell)

Bill Joy

University of California

(For BSD)

The C shell's syntax and

usage are very similar to

the C programming

language.

KSH (Korn SHell)

David Korn

AT & T Bell Labs

Any of the above shell reads command from user (via Keyboard or Mouse) and tells

Linux O/s what users want. If we are giving commands from keyboard it is called

command line interface ( Usually in-front of $ prompt, This prompt is depend upon

your shell and Environment that you set or by your System Administrator,

therefore you may get different prompt ).

NOTE: To find your shell type following command

$ echo $SHELL

How to use Shell

To use shell (You start to use your shell as soon as you log into your system) you

have to simply type commands. Following is the list of common commands.

Linux Common Commands

NOTE that following commands are for New users or for Beginners only. The

purpose is if you use this command you will be more familiar with your shell and

secondly, you need some of these command in your Shell script. If you want to get

more information or help for this command try following commands For e.g. To see

help or options related with date command try

$ date --help

or To see help or options related with ls command (Here you will screen by screen

help, since help of ls command is quite big that can't fit on single screen )

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Linux Shell Script Tutorial

$ ls --help | more

Syntax: command-name --help

Syntax: man command-name

Syntax: info command-name

See what happened when you type following

$ man ls

$ info bash

NOTE: In MS-DOS, you get help by using /? clue or by typing help command as

C:\> dir /?

C:\> date /?

C:\> help time

C:\> help date

C:\> help

Linux Command

For this Purpose

Use this Command Syntax

Example ( In front of $

Prompt)

To see date

date

$ date

To see who's using

system.

who

$ who

Print working directory pwd

$ pwd

List name of files in

current directory

ls or dirs

$ ls

To create text file

NOTE: Press and hold

CTRL key and press D to

stop or to end file

( CTRL+D )

cat > { file name }

$ cat > myfile

type your text

when done press

To text see files

cat {file name }

$ cat myfile

To display file one full

screen at a time

more {file name }

$ more myfile

To move or rename

file/directory

mv {file1} {file2}

$ mv sales

sales.99

To create multiple file

copies with various link.

After this both oldfile

newfile refers to same

name

ln {oldfile} {newfile}

$ ln Page1 Book1

To remove file

rm file1

$ rm myfile

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