View source for PERL/C2/for-for-each-loops/English

'''Title Of Script: '''for & foreach Loops in Perl

'''Author:''' Amol Brahmankar

'''Keywords:''' Loops in Perl, for loop in perl, foreach in perl, video tutorial.



{| style="border-spacing:0;"
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| <center>'''Visual Clue'''</center>
| style="border:0.05pt solid #000000;padding:0.097cm;"| <center>'''Narration'''</center>

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Slide
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Welcome to the spoken tutorial on '''for '''and''' foreach Loops''' in '''Perl'''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Slide: Learning Objectives
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| In this tutorial, we will learn about:

'''for''' loop in '''Perl '''and

'''foreach''' loop in '''Perl'''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Slide: System Requirements
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| I am using '''Ubuntu Linux12.04''' operating system and '''Perl 5.14.2'''


I will also be using the '''gedit '''Text Editor.


You can use any text editor of your choice.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Slide: Prerequisites
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| You should have basic knowledge of '''Variables '''and''' Comments '''in''' Perl.'''


If not, please go through the relevant spoken tutorials on the '''spoken tutorial '''website.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Slide
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| '''Perl''' provides a mechanism by which we can check a condition repeatedly for various values. This is done using '''loops'''.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Slide
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| There are various types of loops in Perl;

'''for loop'''

'''foreach loop'''

'''while loop &'''

'''do-while loop'''


In this tutorial, we'll cover '''for''' and '''foreach loop'''.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Slide
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| '''for '''loop in '''Perl''' can be used to execute a piece of code for a certain number of times.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Slide


'''for (variable initialization; condition; increment/decrement) '''

'''{'''

'''Piece of code to be executed multiple times'''

'''}'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| The syntax of '''for loop''' is as follows:


'''for space open bracket variable initialization semicolon condition semicolon increment close bracket'''


Press '''Enter'''


Open curly brackets


Piece of code to be executed multiple times


Close curly brackets




|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| 
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Now let us look at an example of a '''for '''loop.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Switch to the Terminal and type

'''gedit forLoop.pl &'''

and press '''Enter'''.
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Open the '''Terminal''' and type;

'''gedit forLoop.pl space & (ampersand)'''

and press''' Enter'''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Point to the filename '''forLoop'''.'''pl''' in the Titlebar of gedit.
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| This will open the '''forLoop'''.'''pl''' file in '''gedit'''.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Type the piece of code and '''save''' the file


'''<nowiki>#!/usr/bin/perl</nowiki>'''


'''<nowiki>for ($i=0; $i<=4; $i++) {</nowiki>'''

'''print “Value of i: $i\n”;'''

'''}'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Type the following piece of code;


'''hash exclamation mark slash u s r slash bin slash perl'''


Press '''Enter'''


'''for space open bracket dollar i equals to zero semicolon space dollar i less than or equal to four semicolon space dollar i plus plus close bracket'''

space

Open curly bracket 

press enter , type

'''print space double quote Value of i colon space dollar I slash n double quote complete semicolon '''


And Press '''Enter'''

now

 ANd Close curly bracket




|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Press '''ctrl+s'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Press '''Ctrl+S''' to '''save''' the file.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Highlight '''$i=0'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Let me explain what the '''for''' loop does.


The variable '''i''' is initialized to zero.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Highlight '''<nowiki>$i<=4</nowiki>'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Next, the condition is checked. 

In this case, the condition is '''i is less than or equal to 4'''.


If this condition is true, the code within the curly bracket will be executed.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Highlight '''print'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| This means the first '''print''' statement 

'''“Value of i: 0”'''

will be displayed on the '''terminal'''.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Highlight '''$i++'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| After this, the variable '''i''' is incremented by '''1.''' 

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Highlight '''<nowiki>$i<=4</nowiki>'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| And the '''for''' loop condition is checked once again.


This loop will exit when the value of''' i''' becomes greater than '''4'''.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| 
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| In this case, the '''for''' loop will be executed for '''i = 0, 1, 2, 3, 4'''


which is a total of '''5 '''times.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Switch to '''terminal'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Now, switch to the '''terminal'''.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| '''perl -c forLoop.pl'''



| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Type the following to check for any compilation or syntax error:


'''perl hyphen c forLoop dot pl'''


and press''' Enter.'''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Highlight the below line on terminal;

'''forLoop.pl syntax OK'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Here it displays a message 

'''forLoop.pl syntax OK'''


So, we have no errors.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Execute perl script


'''perl forLoop.pl'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Now, let's execute the '''Perl''' script by typing


'''perl forLoop dot pl'''


and press '''Enter.'''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Highlight/point to the output of the perl script on terminal

'''Value of i: 0'''

'''Value of i: 1'''

'''Value of i: 2'''

'''Value of i: 3'''

'''Value of i: 4'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| The following output will be shown on terminal.




|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| 
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Now, let us look at the '''foreach '''loop.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Slide
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| If we want to iterate a condition for an '''array''', we can make use of '''foreach '''loop.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Slide


'''foreach $variable (@array) {'''

'''perform action on each element of an array'''

'''}'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| The syntax is:


'''foreach space dollar variable space within brackets at the rate array '''


'''space '''


open curly bracket 


'''perform action on each element of an array '''


Press '''Enter'''

Close the curly bracket.


'''Please note: '''We'll cover array, array initialization and defining an array in subsequent tutorials.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| 
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Now let us look at an example of '''foreach''' loop.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Switch to the Terminal and type


'''gedit foreachLoop.pl &'''


and press '''Enter'''.
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Open the '''Terminal''' and type


'''gedit foreachLoop dot pl space ampersand'''


and Press''' Enter'''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Point to the filename '''foreachLoop'''.'''pl''' in the Titlebar of gedit.
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| This will open the '''foreachLoop'''.'''pl''' file in '''gedit'''.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| '''<nowiki>#!/usr/bin/perl</nowiki>'''


'''@myarray = (10, 20, 30);'''


'''foreach $var (@myarray) {'''

'''print “Element of array is: $var \n”;'''

'''}'''



| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Type the following piece of code


'''hash exclamation mark slash u s r slash bin slash perl'''


and Press '''Enter'''


'''at the rate myarray is equal to open bracket ten comma space twenty comma space thirty close bracket semicolon'''

press enter 

'''foreach space dollar var space open bracket at the rate myarray close bracket space'''


Open curly bracket

press enter and type


'''print space double quote Element of array is colon dollar var space slash n double quote complete semicolon '''


Press '''Enter and'''

Close curly bracket

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Press '''Ctrl+S'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Press '''ctrl+s''' to '''save''' the file.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Highlight

'''@myarray = (10, 20, 30);'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Let me explain what this code does.


An array '''myarray '''is declared. 

It has 3 elements 10, 20 and 30.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Highlight '''$var '''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| In each iteration of foreach loop dollar var will contain the single element of an array

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Highlight '''foreach $var (@myarray)'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| '''foreach '''keyword will repeat this loop for each element of an array.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Highlight '''print “Element of array is:$var \n”;'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| That is, the code within the curly bracket will be executed for each '''myarray '''element.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Highlight '''\n'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| '''Back-slash n''' will place the prompt on a new line.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| 
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| This means the first '''element''' ''''10'''' will be displayed on the terminal.


Then 20 and so on, till all the elements are printed.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Highlight '''foreach '''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| This loop will exit after printing all the elements in '''myarray'''.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Switch to terminal


'''perl -c foreachLoop.pl'''



| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Now, switch to terminal and type the following to check for any compilation or syntax error.

type

'''perl hyphen c foreachLoop dot pl'''


and press''' Enter.'''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Highlight the below line on terminal;

'''foreachLoop.pl syntax OK'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| The following line will be shown on terminal

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Execute perl script


'''perl foreachLoop.pl'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| There are no compilation or syntax errors.

So let us execute the '''Perl''' script.
Type 


'''perl foreachLoop dot pl'''


and press '''Enter'''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Highlight the output of the perl script on terminal 

'''Element of an array is: 10'''

'''Element of an array is: 20'''

'''Element of an array is: 30'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| The following output will be shown on terminal.




|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| 
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| So, that's it about '''for''' loop and '''foreach''' loop.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Slide : Summary
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Let us summarize.

In this tutorial, we have learnt -

'''for''' loop and

'''foreach''' loop in '''Perl'''

using some sample programs.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Assignment
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Here is an assignment for you -

# Declare a string as 'Spoken Tutorial' and 
# Print it 5 times
# Declare an array of colours as @colorArray = ('red', 'white', 'blue') and 
# Print the element of an array using '''foreach''' loop



|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| About the Project
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Watch the video available at the following link


It summaries the Spoken Tutorial project


If you do not have good bandwidth, you can

download and watch it

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Spoken Tutorial Workshops
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| 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 at spoken hyphen tutorial dot org

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| Acknowledgment


http://spoken-tutorial.org\NMEICT-Intro
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| 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


spoken hypen tutorial dot org slash NMEICT hyphen Intro

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.097cm;"| 
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.097cm;"| Hope you enjoyed this Perl tutorial. 

This is Amol Brahmankar signing off.


Thanks for joining.

|}