BASH/C2/Basics-of-Shell-Scripting/English-timed

Time	Narration
00:01	Welcome to the spoken tutorial on Basics of Shell Scripting.
00:05	In this tutorial, we will learn about:
00:09	System variables
00:11	User defined variables and
00:13	Accepting user input via keyboard.
00:16	To follow this tutorial, you should be familiar with Linux Operating System.
00:23	If not, for relevant tutorials, please visit our website which is as shown.
00:29	For this tutorial, I am using:
00:32	Ubuntu Linux 12.04 Operating System and
00:35	GNU Bash version 4.1.10
00:40	Please NoteGNU Bash version 4 or above is recommended for practice.
00:46	Let us start with an introduction to variables.
00:49	Bash variables provide temporary storage for information.
00:55	These variables can be used within the lifespan of the program.
01:01	There are two types of variables: System variables,User defined variables .
01:07	System variables: These are created and maintained by Linux Bash Shell itself.
01:14	They are defined by capital letters.
01:17	Commonly used system variables are-
01:20	BASH_VERSION . HOSTNAME
01:23	HOME etc.
01:25	Let us open the terminal by pressing Ctrl, Alt and T keys simultaneously on your keyboard.
01:33	Now, type: set and press Enter.
01:38	This will display all the system variables.
01:42	Alternately, you can type env or printenv to view all the system variables.
01:53	Let me clear the prompt.
01:55	Now, type: echo space within double quotes dollar sign HOSTNAME
02:01	now press Enter.
02:04	The hostname of the system will be displayed.
02:07	Now let's find out the full path of homedirectory.
02:11	Type: echo space within double quotes dollar sign HOME(in capital).
02:18	Press Enter.
02:21	The full path of user's home directory will be displayed.
02:26	Now, type:
02:27	echo space within double quotes HOME (in capital).
02:32	Press Enter.
02:34	This will display only the "HOME", not the value of HOME variable.
02:39	So, it is necessary to use dollar sign( $) at the beginning of every variable to display its value.
02:48	Let us switch back to our slides.
02:51	User Defined Variables:
02:53	These variables are created and maintained by users.
02:57	It is always a good idea to avoid uppercase for the names of user defined variables.
03:05	This makes it easy to differentiate between user defined and system variables.
03:12	Switch back to our terminal.
03:14	Type: username equal to sign sunita
03:20	Please note that there should not be any blank space between username, equal to sign and sunita.
03:29	Now, press Enter.
03:30	To display the value of variable username,
03:33	Type: echo space within double quotes dollar sign username
03:40	press Enter.
03:42	This will display sunita on your terminal.
03:46	The value of a variable can be unset.
03:50	Let us switch back to our slides.
03:52	unset- the value of a variable can be unset by using the unset command.
03:59	The syntax for this is- unset variablename
04:03	Let's use the previous example where username is our variable.
04:08	Switch to the Terminal. Now type: unset space username, press Enter.
04:18	Let us check. Type: echo space within double quotes dollar sign username press Enter.
04:28	Nothing will be displayed on the terminal.
04:30	This means that the value of variable username has been removed.
04:36	Now switch back to our slide.
04:39	Global and local variables:
04:42	In Shell script, user defined variables can be declared globally or locally.
04:49	By default, all variables are global.
04:52	This means, their values remain the same inside and outside the function.
04:59	Let us learn how to declare variables globally and locally.
05:04	Switch to the terminal . Type:
05:07	gedit space g_(underscore)variable.sh space & (ampersand sign).
05:16	gedit is the text editor g_(underscore) variable.sh is our file name
05:23	and '&' (ampersand) is used to free up the prompt.
05:28	Press Enter.
05:30	Type the code as shown here, in your "g_(underscore)variable.sh" file.
05:35	Let me explain the code now.
05:38	The first line with the hash and exclamation symbol is a shebang or a bang line.
05:44	username=sunita is the userdefined variable and it is declared globally.
05:51	echo will display the string "outside function:" and
05:55	dollar username will print the value of the variable username.
06:00	This is how we define a function in BASH script.
06:04	We will discuss about functions in detail, in later tutorials.
06:09	This is the body of the function.
06:12	Here, another message "inside function" will be displayed along with the value of username.
06:19	Here, we call the function.
06:21	This is our code. Now let's execute it.
06:23	Come back to our Terminal.
06:26	Let me clear the prompt.
06:28	First we need to make our file executable.
06:31	Type: chmod space plus x space g_(underscore)variable.sh, press Enter.
06:39	Now, type: dot slash g_(Underscore)variable.sh
06:45	Press Enter.
06:47	Observe the output. Outside the function, username takes the value sunita.
06:53	Inside the function also, username takes the same value sunita.
06:59	This is because username was declared globally outside the function.
07:04	Next, let us learn how to declare a variable locally.
07:09	Type: gedit space l_(Underscore)variable.sh space & (ampersand sign).
07:18	Press Enter.
07:20	Type the code as shown here, in your "l_(underscore)variable.sh" file.
07:25	Let me explain the code.
07:28	The code is the same as before except for an extra line of code inside the function.
07:36	Inside the function block, we have a line- local space username equals to jack.
07:41	This assigns a new value for the variable username locally.
07:48	Now switch to the Terminal.
07:50	Let's make the file executable
07:52	by typing chmod space plus x space l_variable.sh
08:00	Press Enter.
08:02	Type: dot slash l_variable.sh
08:07	Press Enter.The output is displayed.
08:10	Outside the function, username takes the value sunita
08:15	whereas inside the function, username takes the value jack.
08:20	This is because username is assigned this value locally, within the function.
08:26	Now let us quickly see how to get user input via keyboard.
08:31	The read command is used to accept input from the keyboard.
08:36	It can also be used to assign an input value to a user defined variable.
08:41	The syntax of read command is-
08:44	read space hyphen p space within double quotes PROMPT
08:50	Please note that PROMPT is just a string that waits for user input.
08:55	You may replace it with your own string.
08:58	Now, switch to the terminal .
09:00	Type: gedit space read.sh space & (ampersand sign)
09:08	Press Enter. Type the code as shown here in your "read.sh" file.
09:14	Let me explain the code.
09:16	In this example, input is given from the keyboard by the user.
09:21	This is the bang line.
09:23	Here -p displays the prompt without a newline and takes input from the keyboard.
09:31	The user input will be stored in the variable username.
09:36	echo command displays the message
09:38	Hello and the name entered by the user via the keyboard.
09:43	So, let us execute the program.
09:45	Come back to our terminal.
09:49	Type: chmod space plus x space read.sh
09:55	press Enter.
09:56	Type: dot slash read.sh press Enter.
10:01	Here it is displayed Enter username:
10:04	I will type ashwini, press Enter.
10:08	The message Hello ashwini is displayed.
10:13	ashwini was assigned as an input value to the user defined variable username.
10:20	Let us go back to our slides and summarize.
10:23	In this tutorial, we learnt:
10:26	System variables , User defined variables and
10:29	Accepting user input via keyboard.
10:33	As an assignment- Write a simple Bash program to get the following system variables.
10:38	pwd and * logname.
10:41	Write a simple Bash program
10:43	to ask username from user
10:46	to exit the program, if user does not enter anything within 10 seconds.
10:51	{Hint: read -(Hyphen)t 10 -(Hyphen)p}
10:56	Watch the video available at the link shown below.
10:59	It summarizes the Spoken-Tutorial project.
11:02	If you do not have good bandwidth, you can download and watch it.
11:07	The Spoken Tutorial Project team: Conducts workshops using spoken tutorials.Gives certificates to those who pass an online test.
11:16	For more details, please write to contact@spoken-tutorial.org
11:23	Spoken Tutorial Project is a part of the Talk to a Teacher project.
11:27	It is supported by the National Mission on Education through ICT, MHRD, Government of India.
11:34	More information on this mission is available at the link shown below: http://spoken-tutorial.org/NMEICT-Intro
11:40	The script has been contributed by FOSSEE and Spoken Tutorial teams.
11:44	This is Ashwini Patil from IIT Bombay, signing off. Thank you for joining.

Contributors and Content Editors

PoojaMoolya, Pratik kamble, Sandhya.np14