BASH/C3/More-on-functions/English

Title of script: More on functions

Author: Lavitha Pereira

Keywords: Video tutorial, Bash shell, function, function call

Visual Cue	Narration
Display Slide 1	Dear friends, Welcome to the spoken tutorial on More on functions
Display Slide 2	In this tutorial, we will learn To pass an argument to a function Define local variable within a function and Define global variable in a function With the help of some examples
Display Slide 3Prerequisites	To follow this tutorial you should have knowledge of Shell Scripting in BASH. If not, for relevant tutorials please visit our website which is as shown,(http://www.spoken-tutorial.org)
Display Slide 4 System requirements	For this tutorial I am using Ubuntu Linux 12.04 Operating System and GNU BASH version 4.2 Please note, GNU Bash version 4 or above is recommended to practice this tutorial.
	Let us first learn how to pass an argument to a function, and its usage.
	Let me open a file 'function_parameters.sh'
Highlight #!/usr/bin/env bash	This is the shebang line.
Highlight say_welcome() {	Our function name is say_welcome Open curly bracket opens the function definition.
Highlight echo "Welcome to $1 $2"	$1 is the first positional parameter $2 is the second postional parameter
Highlight }	Close curly bracket closes the function definition.
Highlight say_welcome "Bash" "learning"	Here, the function 'say_welcome' is called with arguments. The syntax is, function name i.e. say welcome ...followed by the arguments within double quotes, i.e. Bash and learning.
Highlight say_welcome "functions in" "Bash"	In a similar manner, I will call the same function with a different set of arguments. So, I have say_welcome space within double quote functions in space and within double quote Bash.
Save and Switch to terminal	Save the file and go to the terminal.
Type chmod +x function_parameters.sh>>Press Enter	Type:chmod space plus x space function underscore parameters dot sh Press Enter.
Type ./function_parameters.sh>>Press Enter	Type dot slash function underscore parameters dot sh Press Enter.
Terminal [Output] Welcome to Bash learning Welcome to functions in Bash	We see that the positional parameters were substituted by the arguments passed to the function. Dollar 1($1) was substituted by the string Bash and Dollar 2($2) with learning. Then again, Dollar 1($1) was substituted by functions in and Dollar 2($2) with Bash.
Display slide 5 Local and Global variables in functions	* In Bash, variables can be declared as local variables and global variables. Local variable: It's value will be valid within the function in which it is defined. Local variables are declared using keyword 'local'.
Display slide 6 Local and Global variables in functions	Global variable: The value of a global variable can be accessed throughout a Bash script.
	Let us learn these 2 ways to declare a variable within a function.
	Let me open a file 'function_local.sh'
Highlight #!/usr/bin/env bash	This is the shebang line.
say_hello(){	Function name is say underscore hello
Highlight local first_name=$1 #Local variable	Here, variable first_name is declared with keyword local. Which means, its value will be valid within the function say_hello only.
Highlight last_name=$2 # Global variable	A variable declared without any keyword, is treated as a global variable. So, the variable last_name can be accessed throughout the script.
Highlight echo "Hello $first_name $middle_name $last_name" Highlight }	In this echo line, we will display the value of variables first_name, middle_name and last_name After this, we close this function.
Highlight middle_name="K" #global variable	Now, here the variable middle_name is declared without keyword. So, its value will be global throughout the script.
Highlight say_hello "Pratik" "Patil"	Once again, we will call the function here. We pass two arguments to this function call, namely, “Pratik” and “Patil”.
Highlight echo "My first name is: $first_name" echo "My middle name is: $middle_name" echo "My last name is: $last_name"	These echo statements will display the value of variables $first_name, $middle_name and $last_name
	Please keep in mind that variable first_name is a local variable.
Save and Switch to terminal	Save the file and go to the terminal.
Type chmod +x function_local.sh>>Press Enter	Type:chmod space plus x space function underscore local dot sh Press Enter.
Type ./function_local.sh>> Press Enter	Now type dot slash function underscore local dot sh Press Enter.
Terminal [Output] Hello Pratik K Patil	The first line of output displays the message Hello Pratik K Patil. Here, the variable first_name that contains value “Pratik” is local. Which means the value is limited to the function.
	Now, let us see how the local variable behaves outside the function.
Terminal [Output] My first name is: My middle name is: k My last name is: Patil	Here, nothing is displayed in first_name. This is because the value of first_name is local to the function. And it is not available outside the function. middle_name and last_name are printed as they are global variables.
	Hope the difference is clear to you. Let us now summarise.
Display Slide 7 Summary	In this tutorial, we learnt To pass arguments to a function To declare Local variable in a function To declare Global variable in a function with the help of a few examples
Display Slide 7 Assignment	As an assignment. Write a program, Where the function accepts two arguments. The function should multiply the two arguments. Make 3 function calls with arguments (1, 2), (2, 3) and (3, 4)
Display Slide 8 http://spoken-tutorial.org /What\_is\_a\_Spoken\_Tutorial About the Spoken Tutorial Project	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 9 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 10 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
Display Slide 11	The script has been contributed by FOSSEE and Spoken-Tutorial teams. This is Ashwini Patil from IIT Bombay signing off. Thank you for joining.

Contributors and Content Editors

Ashwini, Nancyvarkey