BASH/C3/Arrays-and-functions/English

Title of script: Arrays & 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 Arrays & functions
Display Slide 2	In this tutorial, we will learn To pass an array to a function Use of exit statement in a function Use of return statement in a function With the help of some examples
Display Slide 3Prerequisites	To follow this tutorial you should have knowledge of Shell Scripting. You should also have knowledge of arrays and if statement 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.
Pass an array to a function	Let us first learn how to pass an array to a function, and its usage.
	Let me open a file 'function_array.sh'
#!/usr/bin/env bash	This is the shebang line.
array_display() {	Our function name is array_display Open curly bracket opens the function definition.
[Highlight] array=($@) #Takes array name as variable	The use of Dollar At-sign was explained in previous tutorials in this series. Basically, it is used to print all arguments passed to a function. Dollar At sign within round brackets stores array elements in variable 'array'.
echo " Array elements are: ${array[@]}" #displays all element of an array	Dollar opening curly brace array within square bracket At sign closing curly brace This line of code displays all the elements of an array.
echo "Second element i: ${array[1]}" #displays the 2nd element return 0 }	Dollar opening curly brace array within square bracket one closing curly brace This line of code displays the second element of the array.
[Highlight] operating_systems=(Ubuntu Fedora Redhat Suse)	operating_systems is declared with the elements Ubuntu, Fedora, Redhat and Suse
array_display ${operating_systems[@]}	Here, array 'operating_systems' is passed to the function 'array_display'.
Display slide 5 Pass an array to a function Syntax: function_name ${array_name[@]}	The syntax to pass an array to a function is: function_name space dollar opening curly brace array_name within square bracket 'At sign' closing curly brace
	Come back to our program.
colors=(White green red blue) array_display ${colors[@]}	Similarly, 'colors' is declared with the elements White, green, red and blue Here, array 'colors' is passed to the function 'array_display'.
Save and Switch to terminal	Now let's save the file and go to the terminal.
Type chmod +x function_array.sh>>Press Enter	Type:chmod space plus x space function underscore array dot sh Press Enter.
Type, ./function_array.sh>>Press Enter	Type dot slash function underscore array dot sh Press Enter.
Terminal [Output] Array elemnts are: Ubuntu Fedora Redhat Suse Second element is: Fedora Array elements are: White green red blue Second element is: green	As we can see, array elements of 'operating_systems' and 'colors' are displayed. And the second array element of 'operating_systems' and 'colors' are also displayed.
Display slide 6 'return' and 'exit' statement in functions	In Bash, 'exit' and 'return' statements gives status code of a function or a program.
Display slide 7 Return and exit in functions	return: The return statement will return to the script from where it was called. exit: exit statement will end the entire script from where it is encountered.
	Let us learn these 2 ways to return within a function.
Open file return_exit.sh	Let me open a file 'return_exit.sh'
Highlight #!/usr/bin/env bash	This is the shebang line.
function return_function	Function name is return_function
Highlight {	Open curly brace opens the function definition.
if [ $1 == $2 ]; then	This if statement compares two variables. If the two variables are equal, then commands in 'if' are executed.
echo "This is return function" return 0 #Returns to main program	This echo statement displays the message This is return function. return 0 moves the control from function to main program with status code 0(zero).
[Highlight] echo "This will not appear"	Note that the statements after return will not be executed in a function.
fi }	fi indicates the end of if statement
function exit_function {	Here the function name is exit_function
if [ $1 == $2 ]; then	The if statement here compares two variables. If the two variables are equal, then the commands in 'if' are executed.
echo "This is exit function"	This echo statement displays the message "This is exit function"
exit 0	exit 0 will terminate the program.
fi }	fi indicates the end of this if statement.
return_function 3 3	This is a function call with arguments 3 and 3.
echo "We are in main program"	This displays the message "We are in main program"
exit_function 3 3	This is another function call with arguments 3 and 3.
Highlight echo "This line is not displayed"	This echo statement displays the message "This line is not displayed"
	Note that exit will terminate the program. Anything after 'exit' will not be executed.
Save and Switch to terminal	Save the file and go to the terminal.
Type chmod +x return_exit.sh>>Press Enter	Type:chmod space plus x space return underscore exit dot sh Press Enter.
Type ./return_exit.sh>> Press Enter	Now type dot slash return underscore exit dot sh Press Enter.
Terminal [Output] This is return function We are in main program This is exit function	The output displays the messages as shown. Now, let us understand the flow of the program.
Workflow of Program: [Highlight program and explain]	The control will be in main program, which is the script itself. The control goes to 'return_function' because of the function call. As the two variables are equal, it displays the message "This is return function" Then it encounters return 0. And the control flows from function to the statement below the function call, in the main program. Then it displays the message "We are in main program" After that, the control goes to 'exit_function' because of the function call. As the two variables are equal, it displays the message "This is exit function" Then it encounters exit 0. This will terminate the program. Any statement after exit will not be executed. Also, the statement: "This line is not displayed" ` will not be executed.
	Hope the difference is clear to you. Let us now summarise.
Display Slide 8 Summary	In this tutorial, we learnt To pass an array to a function Use of exit in a function Use of return in a function With the help of some examples
Display Slide 9 Assignment	As an assignment. Write a program, Where a function adds all the elements in an array The function should display the sum of elements. Make 2 function calls with array elements (1, 2, 3) and (4, 5, 6)
Display Slide 10 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 11 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 12 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 13	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