BASH/C3/Basics-of-functions/English

Title of script: Basics of functions in Bash

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 Basics of functions in Bash.
Display Slide 2	In this tutorial, we will learn Importance of Functions To declare a function To call a function Work flow of a function with the help of an example
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 Till now we were using GNU BASH version 4.1.10 From now onwards, we will use GNU BASH version 4.2 Please note, GNU Bash version 4 or above is recommended for practice.
	Let us see what is a function and its usage.
Display Slide 5 Functions	A function is a collection of commands or an algorithm. It is intended to do a specific task. It is used to break up a complex program into separate tasks. This improves overall script readability and ease of use.
	There are two syntaxes for function declaration.
Display Slide 6 Function declaration Syntax 1: function function_name { Commands }	First syntax is function space function_name within curly brackets, the commands to be executed
Display Slide 7 Function declaration Syntax 2: function_name() { Commands }	The second syntax is function_name open and close round brackets within curly barckets, the commands to be executed
Display Slide 8 Function call Function_name	Function call Function can be called anywhere within the program. Type the function name at the location where you want to call it. The syntax is the function name itself.
	Let us understand this with the help of a simple example.
Terminal:gedit function.sh	I have already typed the code in a file function.sh
#!/usr/bin/env bash	This is the shebang line.
[Highlight] function machine #Function declaration	Function is declared by the keyword function followed by function name. Here, function name is machine.
{ # Beginning of Function definition echo -e "\nMachine information:" ; uname -a echo -e "\nUsers logged on:" ; w -h echo -e "\nMachine status :" ; uptime echo -e "\nMemory status :" ; free echo -e "\nFilesystem status :"; df -h # End of Function definition }	The content within curly brackets is called function definition. I have displayed various machine details like- uname -a gives machine information. w -h gives users logged onto system. uptime gives the time since machine was on. free gives memory status. df -h gives filesystem status.
[Highlight] echo “Beginning of main program”	The main program starts here. Here we display the message “Beginning of main program”
machine #This is a function call	Here, machine is a function call.
echo “End of main program”	Here we display the message “End of main program”
Display Slide 8 Workflow	Let us understand the workflow. When the bash interpreter visits the function definition, it simply scans the function. The function is called only when its name appears within the script. When the interpreter reads the function name, it executes the function definition.
Display slide 9 Workflow	The interperter treats function name as a command. Please remember that we have to define the function before calling it.
Switch to terminal>> Type chmod +x function.sh>>Press Enter>>Type	Now go to the terminal. To make this code file executable, type: chmod space plus x space function.sh Press Enter.
./function.sh>>Press Enter	Now type dot slash function.sh Press Enter.
Terminal [Output]	The output i.e. the machine details of my system, are seen on the terminal. Please Note: The output will vary from system to system. This brings us to the end of this tutorial. Come back to our slides.
Display Slide 8 Summary	Let us summarize. In this tutorial we learnt, Importance of functions Function declaration Function call Work flow of function with an example
Display Slide 9 Assignment	As an assignment. Write a program with two functions The first function should display the diskspace usage in human readable form(Hint: df -h) The second function should display the filesystem usage in human readable form(Hint: du -h)
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 team This is Ashwini Patil from IIT Bombay. Signing off Thank you for joining.

Contributors and Content Editors

Ashwini, Nancyvarkey