BASH/C2/Command-Line-arguments-and-Quoting/English-timed

Time	Narration
00:01	Welcome to the spoken tutorial on Command line arguments and Quoting in BASH.
00:08	In this tutorial, we will learn about:
00:11	* Command line Arguments and
00:13	* Quoting.
00:15	To follow this tutorial, you should be familiar with the Linux Operating System.
00:20	If not, for relevant tutorials please visit our website which is as shown.
00:26	For this tutorial, I am using:
00:29	* Ubuntu Linux 12.04 OS
00:33	* GNU Bash version 4.1.10
00:37	GNU Bash version 4 or above is recommended for practice.
00:43	Shell script can accept arguments from the command line.
00:46	An argument is passed to a program being called.
00:52	Any number of arguments can be passed to a program.
00:57	Let us open the terminal by pressing Ctrl, Alt and T keys simultaneously on your keyboard.
01:06	I have already written the code in the file named arg.sh.
01:12	On the terminal, let me open this file by typing:
01:16	gedit space arg.sh space ampersand sign(&).
01:23	We use the ampersand to free up the prompt.
01:27	Now, press Enter.
01:30	The text-editor is opened.
01:33	Let me explain the code now.
01:36	This is the shebang line.
01:39	This line will print the zeroth argument.
01:43	Here, $0 (Dollar zero) will print the name of the shell script.
01:48	This, in turn, means that the zeroth argument is the name of the program itself.
01:55	Let us execute the program and see.
01:59	Switch to the terminal.
02:01	First, make the file executable by typing:
02:05	chmod space plus x space arg.sh
02:12	Press Enter.
02:14	Now, type: dot slash arg.sh
02:18	Press Enter.
02:19	The output is displayed as: Zeroth argument is arg.sh.
02:26	Now, come back to our editor and type the three lines as shown here.
02:33	$1 (Dollar one) represents the first argument passed to the program from the command line.
02:40	$2 (Dollar two) represents the second argument passed to the program.
02:44	And $3 (Dollar three) represents the third argument.
02:48	Now, click on Save.
02:49	Let us execute the program and see.
02:52	Press the up-arrow key, press Enter.
02:57	We see that the zeroth argument is printed.
03:00	But the first, second and third arguments are blank.
03:05	This is because the command line arguments are given during execution.
03:11	Hence, press the up-arrow key and type: sunday monday and tuesday
03:18	Press Enter.
03:21	You can see that the first, second and third arguments are sunday monday and tuesday.
03:28	Now switch back to our editor. Press Enter.
03:33	Now type the line as shown here.
03:37	$12 (Dollar twelve) represents the twelveth argument.
03:41	To write an argument greater than 9, we need to use curly brackets
03:46	else bash will only take the argument of the integer in the ten's place
03:53	and you will not get expected output.
03:57	Now click on Save.
03:59	Let us execute the program.
04:01	Switch to the terminal.
04:04	Let me clear the prompt.
04:07	Now we need to give 12 or 13 arguments to the program.
04:12	Hence, type: dot slash arg.sh space 1 to 13. Now press Enter.
04:23	You can see that the 12th argument is 12.
04:27	Come back to our editor
04:30	and type the line as shown here.
04:34	$# (Dollar hash) gives the total number of arguments that have been passed to a program.
04:40	Now click on Save.
04:43	Let us execute.
04:44	Switch to the terminal.
04:46	Let us execute. Press the up-arrow key and press Enter.
04:52	We can see that the total arguments are 13.
04:57	Now switch to the editor.
05:00	Press Enter and type the lines as shown here.
05:04	$* (Dollar asterisk) will print all the arguments on a single line.
05:10	We will test this with the help of a simple for loop.
05:14	We will analyze this for loop at the time of execution.
05:18	Now click on Save. Switch to the terminal.
05:22	Let me clear the prompt.
05:26	Now, let us type: dot slash arg.sh space sunday monday and tuesday
05:35	Press Enter.
05:38	You can see that the total number of arguments are 3 as we have passed 3 arguments to our program.
05:46	As already said, $* will print all the arguments on a single line.
05:54	And this is the output for the for loop.
05:57	We see that all the arguments are printed on the single line.
06:02	Now, move back to our program and type the lines as shown here.
06:09	$@ (Dollar at) will also print all the arguments.
06:13	However, this time each argument will be printed on separate line.
06:20	This is another for loop which will print each argument in a separate line.
06:26	Let us see how. Click on Save.
06:29	Switch to the terminal.
06:32	Press the up-arrow key.
06:34	Press Enter. You can see the difference now.
06:39	These are the arguments printed by $@.
06:43	$@ prints each argument on separate line.
06:47	This is the output for the 2nd for loop.
06:52	Now let's move on to quoting in BASH
06:55	Switch to the slides.
06:57	There are three types of quotes:
06:59	* Double quote
07:00	* Single quote
07:02	* Backslash.
07:03	Double quote substitutes the value of variables and commands.
07:09	Example echo “Username is $USER”.
07:13	It displays your username of the system.
07:17	Switch to the Terminal.
07:20	Let me clear the prompt.
07:23	Now, type: echo space within double quotes Username space is dollar USER in capitals.
07:34	Press Enter.
07:35	The username of the system is printed.
07:39	The output will vary according to your system.
07:42	Now move back to slides.
07:46	Single quotes preserves the literal meaning of each character of the given string.
07:53	It is used to turn off special meaning of all characters.
07:58	Switch to the Terminal.
08:01	Type: echo space within single quote Username is dollar USER in capital.
08:10	Press Enter.
08:12	The output is Username is $USER.
08:16	In this example, it prints all the characters which appear within the single quotes.
08:23	It does not substitute the value of variable $USER.
08:28	Switch back to our slides.
08:31	Backslash removes the special meaning from a single character.
08:37	It is used as an escape character in BASH.
08:42	Switch to the Terminal.
08:44	Now, type: echo space within double quote Username is backslash dollar USER (in capital).
08:55	Since we have given double quotes, we expect the echo command to display the username.
09:02	Let's try this command, so press Enter.
09:06	The output is Username is $USER
09:10	In this example the backslash removes the special meaning of (Dollar) $ symbol.
09:16	$USER is just treated as a string without any special functionality.
09:22	This brings us to the end of this tutorial.
09:25	Switch back to our slides.
09:27	Let us summarize.
09:28	In this tutorial, we learnt:
09:31	* Command line arguments
09:33	* Functionality of Double quote, Single quote and Backslash.
09:39	Watch the video available at the link shown below.
09:42	It summarizes the Spoken Tutorial project.
09:45	If you do not have good bandwidth, you can download and watch it.
09:51	The Spoken Tutorial Project team: Conducts workshops using spoken tutorials.
09:56	Gives certificates to those who pass an online test.
10:00	For more details, please write to contact@spoken-tutorial.org
10:07	Spoken Tutorial Project is a part of the "Talk to a Teacher" project.
10:10	It is supported by the National Mission on Education through ICT, MHRD, Government of India. More information on this mission is available at: http://spoken-tutorial.org\NMEICT-Intro
10:24	The script has been contributed by FOSSEE and spoken-tutorial team.
10:30	And this is Ashwini Patil from IIT Bombay, signing off. Thank you for joining.

Contributors and Content Editors

Gaurav, Pratik kamble, Sandhya.np14