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

Title of script: Command line arguments and Quoting

Author: FOSSEE and spoken-tutorial team

Keywords: Video tutorial, Command Line Arguments, Single quote, Double quote, Backslash

Visual Cue	Narration
Display Slide	Welcome to the spoken tutorial on Command line arguments and Quoting in BASH
Display Slide	In this tutorial, we will learn about Command line Arguments Quoting
Display Slide Prerequisites spoken-tutorial.org	To follow this tutorial, you should be familiar with the Linux Operating System. If not, for relevant tutorials please visit spoken hyphen tutorial dot org.
Display Slide System Requirements	For this tutorial I am using Ubuntu Linux 12.04 OS and GNU Bash version 4.1.10 GNU Bash version 4 or above is recommended to practise this tutorial.
Display slide : Command Line arguments	* Shell script accepts arguments from the command line. The arguments are passed to the program being called. Any number of arguments can be passed to a program.
Press Ctrl+Alt+T	Let us open the terminal by pressing Ctrl+Alt+T keys.
On terminal>> Type gedit arg.sh&>> press Enter	I have already written the code in the file named arg.sh On the terminal, let me open this file by typing, gedit space arg.sh ampersand Here ampersand is used to free up the prompt. Press Enter.
	Let me explain the code now.
#!/bin/bash	This is a shenbang or a bang line.
[highlight] echo "zeroth arg: $0"	This line will print the Zeroth argument. Here, $0 (Dollar zero) will print the name of the shell script. This in turn means that, the zeroth argument is the name of the program itself.
[highlight] echo "first arg: $1"	$1 (Dollar one) represents the first argument passed to the program from the command line.
[highlight] echo "second arg: $2"	Similarly, $2 (Dollar two) represents the second argument passed to the program.
[highlight] echo "third arg: $3"	$3 (Dollar three) represents the third argument.
[highlight] echo "twelveth arg: ${12}"	And $12 (Dollar twelve) represents the twelveth argument.
[highlight again!!] echo "twelveth arg: ${12}"	To write an argument greater than 9, we need to use curly brackets. Else bash will only take the argument of the integer in the ten's place. And you will not get expected output.
echo "total args: $#"	To continue with our code - $# (Dollar hash) gives the total number of arguments that have been passed to a program.
echo "Args(dollar *): $*" for arg in “$*” do echo “$arg” done	$* (Dollar asterix) will print all the arguments on a single line. We will test this with the help of a simple for loop. We will analyse this for loop at the time of execution.
echo "Args(dollar @): $@" for arg in “$@” do echo “$arg” done	$@ (Dollar at) will also print all the arguments. However, this time each argument will be on a seperate line. This is another for loop, which will print each argument in a seperate line.
exit 0	exit 0 will exit the program.
	Now, save the file.
Switch to terminal Type: chmod +x arg.sh Press Enter	And make it executable by typing, chmod space plus x space arg.sh and press Enter.
	Command line arguments are given during execution.
Highlight: Type: ./arg.sh sunday monday tuesday Press Enter	Now let us execute our Shell script by typing dot slash arg.sh space sunday space monday space tuesday Here sunday, monday and tuesday are the arguments we are passing. Now press Enter.
	Let me explain the output.
Output: zeroth arg: ./arg.sh	The zeroth argument always displays the command used to execute the program. So, you will see ./arg.sh here.
Output: first arg: sunday second arg: monday third arg: tuesday	sunday is assigned to the first argument. monday is assigned to the second argument. and tuesday is assigned to the third argument.
Output: twelveth arg:	Twelveth argument is empty. This is because we have passed only three arguments to the program. Recall, this was the argument with curly brackets.
Output: total args: 3	We can see that total number of arguments i.e. 3, is assigned to $# (Dollar hash)
Args(dollar *): sunday monday tuesday	As we already said earlier, $* (Dollar asterix) will print all the arguments as on a single line.
sunday monday tuesday	This is the output of the first for loop. We see that all arguments are printed on a single line.
Args(dollar @): sunday monday tuesday	These are the arguments printed by $@ (Dollar at)
sunday monday tuesday	And this is the output of the second for loop. $@ (Dollar at) prints each argument on a seperate line.
	<<PAUSE>> Let's move on. Next, lets see Quoting is BASH. Switch to the slides.
Display slide Quoting	There are three types of quotes in BASH Double quote Single quote Backslash
Display Slide Double Quote	* Double quote substitutes the value of variables and commands Example: echo “Username is $USER” It displays your username on the system.
Switch to terminal>>Type echo “Username is $USER”>> press Enter	Let's switch to Terminal. Type echo space opening double quote Username space is space dollar sign in capitals USER closing double quote and Press Enter
Output: Highlight “Username is lavitha”	This will display your username <<PAUSE>> Let us switch to the slides.
Display Slide Single Quote	* Single quotes preserves the literal meaning of each character of the given string. It is used to turn off special meaning of all characters.
Switch to terminal>>Type echo 'Username is $USER'>> press Enter	Switch to Terminal. Type echo space open single quote Username space is space dollar sign in capitals USER close single quote and Press Enter
Output Highlight: Username is $USER .	The output is Username is $USER In this example, it prints all the characters which appear within the single quotes. It does not substitute the value of variable $USER <<PAUSE>> Switch back to the slides.
Display Slide Backslash	* Backslash removes the special meaning from a single character It is used as an escape character in BASH
Switch to terminal>>Type echo Username is \$USER>> press Enter	Switch to Terminal. Type echo space open double quote Username space is space backslash dollar sign in capitals USER close double quote Since we have given double quotes, we expect the echo command to display the username. Let's try this command; so press Enter.
Output: Highlight Username is $USER	The output is Username is $USER In this example the backslash removes the special meaning of (Dollar) $ symbol. $USER is just treated as a string without any special functionality. <<PAUSE>>
	This brings us to the end of this tutorial. Let us switch back to slides and summarize.
Display slide Summary	In this tutorial we learnt, Command line arguments Functionality of Double quote, Single quote and Backslash
Display Slide	Watch the video available at the link shown below It summarises the Spoken Tutorial project If you do not have good bandwidth, you can download and watch it
Display Slide Spoken Tutorial Workshops	The Spoken Tutorial Project Team Conducts workshops using spoken tutorials Gives certificates to those who pass an online test For more details, please write to contact@spoken-tutorial.org
Display Slide Acknowledgement	Spoken Tutorial Project is a part of the Talk to a Teacher project 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
Keep the same narration as Bash-1 and Bash-2 scripts for consistency.Reply to nancy (26/06/2013, 11:35): "..." Resolved	The script has been contributed by FOSSEE and spoken-tutorial Team. And this is Ashwini Patil from IIT Bombay signing off. Thank you for joining.

Contributors and Content Editors

Ashwini, Gaurav, Nancyvarkey