Difference between revisions of "BASH"

Revision as of 15:02, 23 April 2013

Linux is one of the most popular Operating Systems used in today's world. Linux refers to the family of Unix-like computer operating systems using the Linux kernel. Linux can be installed on a wide variety of computer hardware, ranging from mobile phones, tablet computers and video game consoles to mainframes and supercomputers.

It is an opensource software and the Linux kernel is released under the GNU General Public License and hence can be freely created, modified and distributed.

Linux is actually just a kernel. Many people have put together distributions (often called flavors), that contain not just the kernel but also many other programming tools and utilities. Some well-known distributions include Red Hat Linux, Ubuntu, SuSE Linux, and Debian GNU/Linux.

The real power of Linux can be tapped by using its wide and powerful storehouse of commands which need to be typed in on the terminal. The reason behind this is the fact that Linux can trace its intellectual heritage, if not its source code, to the Unix OS. Unix was developed much before GUI environments were dreamt of. Thus, Unix (and hence Linux) provides a wide array of flexible text-mode commands.

In this tutorial we would mainly concentrate on how to use the wide variety of commands of Linux to handle files,directories,processes etc. These tutorials are created using Ubuntu version 9.04 and above. Please see the associated text box of individual spoken tutorials on the website to decide the versions of Linux OS to which it is applicable.

The Spoken Tutorial Effort for Linux is being contributed by Ms. Ashwini Patil and Lavitha from IIT Bombay and Mr. Sachin Patil.

Linux Slide Template (TEX Format)                                                                                                                               Glossary
                                         (PPT Format)
                                         (ODP Format)

BASH Shell Scripting

1. Introduction to BASH Shell Scripting
   • The bash shell
     • Bash Shell is a Command language interpreter that executes commands.
     • commands are read from input device.
     • input can be your keyboard or from a external file.
   • Bash Shell Script
     • Series of BASH commands written seqentially in plain text file
   • Hello, World! Tutorial
     • creating a simple 'hello_world.sh' file using vim editor.
   • Shebang [#!/bin/bash]
     • The first line of every script is called a shebang.
     • It consists of a number sign and an exclamation point character (#!), followed by the full path to the interpreter such as /bin/bash.
   • Shell Comments
     • adding comments in your BASH programs, to make it more readable using '#'
   • echo Statement
     • printing a message on the screen using ECHO statement.
   • exit status
     • terminating your script using EXIT command and returning a numerical value
   • Execute a script
     • making the script executable using CHMOD command.
   • Debug a script
     • turning on the debug mode using 'set -x'
   • Shell Commands
     • Already explained in 'Introduction to linux' section
2. Basics of Shell Scripting
   • Variable in a shell
     • System Variable -These are created and maintained by linux bash shell itself.Commonly used system variables HOSTNAME, HOME, USER.
     • User Defined Variables-These variables are created and maintained by users.
   • Variable Declaration
     • Global variable -By default all the variables are global, i.e their values remains the same in and outside the function.
     • Local variable -To declare variables locally use local.The syntax is local variable=value
   • Getting user input via Keyboard
     • We can accept input from the keyboard and assing an input value to a user defined variable using 'read' command.
   • Command Line arguments
     • A Command line argument is an arguments passed to a program which is been called.
   • Quoting
     • They are three types of quotes
       • 1)Double quote
       • 2)Single quote
       • 3)Backslash
   • Globbing
     • Filename expansion carried by BASH is known as Globbing.
   • The export statement
     • The export command makes available variables to all child processes of the running script or shell
3. Arrays
   • Declaring an Array and Assigning values.
   • Initializing an Array during declaration
   • To find length of Bash Array and length of nth element
   • To print whole Bash Array
4. More on Arrays
   • Extraction of Array elements
   • Search and replace in an Array element
   • To Add an element to an Array
   • To remove an Element from an Array
5. Special operations on Arrays
6. Conditional execution
   • test
   • if...then
   • if...then...else...if
7. More on If loops
   • nested if
   • Multilevel if-then-else
8. Logical Operations
   • logical AND
   • logical OR
   • logical NOT
   • Conditional expression using [
   • Conditional expression using [[
9. Bash comparison
   • Arithmetic comparison
   • String comparison
   • File attributes comparisons
10. Loops
    • The for loop statement
    • Nested for loop statement
    • The while loop statement
    • Use of : to set infinite while loop
    • The until loop statement
    • The select loop statement
    • Exit the select loop statement
    • Using the break statement
    • Using the continue statement
11. The case statement
    • using case
    • creating menus using case
    • multiple options in case
12. Functions
    • Writing your first shell function
    • Displaying functions
    • Removing functions
    • Defining functions
    • Writing functions
    • Calling functions
    • Pass arguments into a function
    • Local variable
    • Returning from a function
    • Source command
    • Recursive function
    • Putting functions in background
13. Redirections (error handling)
    • Input and Output
    • Standard input
    • Standard output
    • Standard error
    • Redirection of both standard error and output
    • Appending redirected output
    • Empty file creation
    • Here documents
    • Here strings
    • Assigns the file descriptor (fd) to file for output
    • Assigns the file descriptor (fd) to file for input
    • Closes the file descriptor (fd)
14. Pipes and filters
    • Linking Commands
    • Multiple commands
    • Putting jobs in background
    • Pipes
    • How to use pipes to connect programs
    • Input redirection in pipes
    • Output redirection in pipes
    • Why use pipes
    • Filters
15. Signals, process and traps
    • Signals
    • What is a Process?
    • How to view Processes
    • Sending signal to Processes
    • Terminating Processes
    • Shell signal values
    • The trap statement
    • How to clear trap
    • Include trap statements in a script
    • Use the trap statement to catch signals and handle errors
    • What is a Subshell?
    • Compound command
    • Exec command
16. Making you shell script interactive (using dialog box)
    • Menu driven scripts
    • Getting information about your system
    • Bash display dialog boxes
    • Dialog customisation with configuration file
    • A yes/no dialog box
    • An input dialog box
    • A password box
    • A menu box
    • A progress bar (gauge box)
    • The form dialog for input