Nancyvarkey at 05:26, 7 March 2014

2014-03-07T05:26:38Z

Nancyvarkey at 05:18, 7 March 2014

2014-03-07T05:18:17Z

Ashwini: Created page with ''''Title of script: Basics of functions in Bash ''' '''Author:''' Lavitha Pereira '''Keywords: Video tutorial, Bash shell, function, function call''' {| style="border-spacing…'

2014-03-04T12:21:05Z

Created page with ''''Title of script: Basics of functions in Bash ''' '''Author:''' Lavitha Pereira '''Keywords: Video tutorial, Bash shell, function, function call''' {| style="border-spacing…'

New page

'''Title of script: Basics of functions in Bash '''

'''Author:''' Lavitha Pereira

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

{| style="border-spacing:0;"
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| <center>'''Visual Cue'''</center>
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| <center>'''Narration'''</center>

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 1
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Dear friends, Welcome to the spoken tutorial on '''Basics of functions in Bash.'''

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 2
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| In this tutorial, we will learn

* Importance of '''Functions'''
* To declare a''' function'''
* To call a''' function'''
* Work flow of a f'''unction'''
* with the help of an example

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 3'''Prerequisites'''

| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| 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)'''

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 4

System requirements
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| 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 to practice this tutorial.

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"|
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us see what is a''' function''' and its usage.

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 5

'''Functions'''

| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| * 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.

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"|
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| There are two syntaxes for '''function''' declaration.

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 6

'''Function declaration'''

Syntax 1:

'''function function_name'''

'''{'''

'''Commands'''

'''}'''
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| First syntax is

'''function space function_name'''

within curly brackets,

the '''commands''' to be executed

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 7

'''Function declaration'''

Syntax 2:

'''function_name()'''

'''{'''

'''commands'''

'''}'''
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The second syntax is

'''function_name open and close round brackets'''

within curly barckets,

the '''commands''' to be executed

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 8

'''Function call'''

'''Function_name'''
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| 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.

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"|
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us understand

* “'''declaration of a function'''” and
* “'''calling a function'''”
* with the help of a simple example.

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Terminal:'''gedit function.sh'''
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| I have already typed the code in a file named '''function.sh'''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''<nowiki>#!/usr/bin/env bash </nowiki>'''
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| This is the''' shebang line'''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''<nowiki>[Highlight]</nowiki>'''

'''function machine '''

<nowiki>#Function declaration </nowiki>
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Function is declared by the keyword '''function''' followed by '''function name'''

Here, '''function name''' is '''machine'''.

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''{ '''

<nowiki># Beginning of Function definition </nowiki>

'''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 '''

<nowiki># End of Function definition </nowiki>

'''} '''
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The content within curly brackets is called '''function definition'''.

Here,

I have displayed various machine details like-

'''uname -a '''gives machine information.

'''w -h '''gives users logged on to system.

'''uptime '''gives the time since machine was on.

'''free''' gives memory status.

'''df -h''' gives filesystem status.

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''<nowiki>[Highlight]</nowiki>'''

'''echo “Beginning of main program”'''

| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The main program starts here.

Here we display the message

“'''Beginning of main program”. '''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''machine '''<nowiki>#This is a function call</nowiki>
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Here,''' machine '''is a '''function call. '''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''echo “End of main program”'''
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Here we display the message

'''“End of main program”'''

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 8

'''Workflow '''

| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| 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.'''<br/>

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display slide 9

'''Workflow'''

| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| # The '''interperter''' treats f'''unction name '''as a command.
# Please remember that we have to '''define''' the '''function''' before '''calling''' it.

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Switch to '''terminal>> '''Type''' chmod +x function.sh>>'''Press '''Enter>>'''Type''' '''

| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Now go to the''' terminal.'''

To make this code file'' ''executable, type:'''chmod space plus x space function.sh'''Press '''Enter.'''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''./function.sh>>'''Press '''Enter'''
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Now type dot slash''' function.sh''' .'''Press Enter.'''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Terminal

<nowiki>[Output]</nowiki>

| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| 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 to summarize.

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 8

'''Summary'''
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us summarize.

In this tutorial we learnt,

* Importance of '''functions'''
* '''Function declaration'''
* '''Function call'''
* Work flow of '''function'''
* with an example

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 9

Assignment
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| 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)'''

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 10

http://spoken-tutorial.org /What\_is\_a\_Spoken\_Tutorial

About the Spoken Tutorial Project
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| 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

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 11

Spoken Tutorial Workshops
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| 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

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 12

Acknowledgement
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| 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

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 13
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The script has been contributed by FOSSEE and spoken-tutorial team

This is Ashwini Patil from IIT Bombay.

Signing off

Thank you for joining.

|}

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BASH/C3/Basics-of-functions/English - Revision history

Nancyvarkey at 05:26, 7 March 2014

Nancyvarkey at 05:18, 7 March 2014

Ashwini: Created page with ''''Title of script: Basics of functions in Bash ''' '''Author:''' Lavitha Pereira '''Keywords: Video tutorial, Bash shell, function, function call''' {| style="border-spacing…'