Linux Shell Scripting Bootcamp: The fastest way to learn Linux shell scripting

James K Lewis

$43.99

3.5 (2 Ratings)

Paperback Jul 2017 208 pages 1st Edition

James K Lewis

$43.99

3.5 (2 Ratings)

Paperback Jul 2017 208 pages 1st Edition

What do you get with Print?

Instant access to your digital eBook copy whilst your Print order is Shipped

Paperback book shipped to your preferred address

Download this book in EPUB and PDF formats

Access this title in our online reader with advanced features

DRM FREE - Read whenever, wherever and however you want

View table of contents

Preview Book

Linux Shell Scripting Bootcamp

Chapter 2. Working with Variables

This chapter will show how variables are used in a Linux system and in scripts.

The topics covered in this chapter are:

Using variables in scripts
Validating parameters using conditional statements
Comparison operators for strings
Environment variables

Validating parameters using conditional statements

Variables can be tested and compared against other variables when using a variable as a number.

Here is a list of some of the operators that can be used:

Operator	Description
`-eq`	This stands for equal to
`-ne`	This stands for not equal to
`-gt`	This stands for greater than
`-lt`	This stands for less than
`-ge`	This stands for greater than or equal to
`-le`	This stands for less than or equal to
`!`	This stands for the negation operator

Let's take a look at this in our next example script:

Chapter 2 - Script 2

#!/bin/sh
#
# 6/13/2017
#
echo "script2"

# Numeric variables
a=100
b=100
c=200
d=300

echo a=$a b=$b c=$c d=$d     # display the values

# Conditional tests
if [ $a -eq $b ] ; then
 echo a equals b
fi

if [ $a -ne $b ] ; then
 echo a does not equal b
fi

if [ $a -gt $c ] ; then
 echo a is greater than c
fi

if [ $a -lt $c ] ; then
 echo a is less than c
fi

if [ $a -ge $d ] ; then
 echo a is greater than...

Comparison operators for strings

The comparison for strings are different than for numbers. Here is a partial list:

Operator	Explanation
`=`	This stands for equal to
`!=`	This stands for not equal to
`>`	This stands for greater than
`<`	This stands for less than

Now let's take a look at Script 3:

Chapter 2 - Script 3

  1  #!/bin/sh
  2  #
  3  # 6/13/2017
  4  #
  5  echo "script3"
  6  
  7  # String variables
  8  str1="Kirk"
  9  str2="Kirk"
 10  str3="Spock"
 11  str3="Dr. McCoy"
 12  str4="Engineer Scott"
 13  str5="A"
 14  str6="B"
 15  
 16  echo str1=$str1 str2=$str2 str3=$str3 str4=$str4
 17  
 18  if [ "$str1" = "$str2" ] ; then
 19   echo str1 equals str2
 20  else
 21   echo str1 does not equal str2
 22  fi
 23  
 24  if [ "$str1" != "$str2" ] ; then
 25   echo str1 does not equal str2
 26  else
 27   echo str1 equals str2
 28  fi
 29  
 30...

Environment variables

So far we have only talked about variables that are local to a script. There are also system wide environment variables (env vars) which play a very important part of any Linux system. Here are a few, some of which the reader may already be aware of:

Variable	Role
`HOME`	user's home directory
`PATH`	directories which are searched for commands
`PS1`	command line prompt
`HOSTNAME`	hostname of the machine
`SHELL`	shell that is being used
`USER`	user of this session
`EDITOR`	text editor to use for `crontab` and other programs
`HISTSIZE`	number of commands that will be shown by the history command
`TERM`	type of command line terminal that is being used

Most of these are self-explanatory, however, I will mention a few.

The PS1 environment variable controls what the shell prompt displays as part of the command line. The default setting is usually something like [guest1@big1 ~]$, which is not as useful as it could be. At a minimum, a good prompt shows...

Download Code

Key benefits

Understand expressions and variables and how to use them practically
Familiarize yourself with the various text filtering tools available in Linux
A fast-paced and concise guide that gets you well versed with linux shell scripting.

Description

Linux Shell Scripting Bootcamp is all about learning the essentials of script creation, validating parameters, and checking for the existence of files and other items needed by the script. We will use scripts to explore iterative operations using loops and learn different types of loop statements, with their differences. Along with this, we will also create a numbered backup script for backup files. Further, you will get well-versed with how variables work on a Linux system and how they relate to scripts. You’ll also learn how to create and call subroutines in a script and create interactive scripts. The most important archive commands, zip and tar, are also discussed for performing backups. Later, you will dive deeper by understanding the use of wget and curl scripts and the use of checksum and file encryption in further chapters. Finally, you will learn how to debug scripts and scripting best practices that will enable you to write a great code every time! By the end of the book, you will be able to write shell scripts that can dig data from the web and process it efficiently.

Who is this book for?

This book is for both GNU/Linux users who want to do amazing things with the shell and for advanced users looking for ways to make their lives with the shell more productive.

What you will learn

Get acquainted with the basics of a shell script to serve as a refresher for more advanced topics
Learn different ways to create and run a script
Discuss the passing and verification of parameters, along with the verification of other items.
Understand the different forms of conditions and loops, and go over the sleep command in detail
Learn about different ways to handle the reporting of return codes
Create an interactive script by reading the keyboard and use subroutines and interrupts
Create scripts to perform backups and go over the use of encryption tools and checksums
Use wget and curl in scripts to get data directly from the Internet

Estimated delivery fee Deliver to South Korea

Standard delivery 10 - 13 business days

$12.95

Premium delivery 5 - 8 business days

$45.95

(Includes tracking information)

What do you get with Print?

Instant access to your digital eBook copy whilst your Print order is Shipped

Paperback book shipped to your preferred address

Download this book in EPUB and PDF formats

Access this title in our online reader with advanced features

DRM FREE - Read whenever, wherever and however you want

Frequently bought together

$99.99

$54.99

$43.99

Total $ 198.97

FAQs

What is the delivery time and cost of print book?

Shipping Details

USA:

Economy: Delivery to most addresses in the US within 10-15 business days

Premium: Trackable Delivery to most addresses in the US within 3-8 business days

UK:

Economy: Delivery to most addresses in the U.K. within 7-9 business days.
Shipments are not trackable

Premium: Trackable delivery to most addresses in the U.K. within 3-4 business days!
Add one extra business day for deliveries to Northern Ireland and Scottish Highlands and islands

EU:

Premium: Trackable delivery to most EU destinations within 4-9 business days.

Australia:

Economy: Can deliver to P. O. Boxes and private residences.
Trackable service with delivery to addresses in Australia only.
Delivery time ranges from 7-9 business days for VIC and 8-10 business days for Interstate metro
Delivery time is up to 15 business days for remote areas of WA, NT & QLD.

Premium: Delivery to addresses in Australia only
Trackable delivery to most P. O. Boxes and private residences in Australia within 4-5 days based on the distance to a destination following dispatch.

India:

Premium: Delivery to most Indian addresses within 5-6 business days

Rest of the World:

Premium: Countries in the American continent: Trackable delivery to most countries within 4-7 business days

Asia:

Premium: Delivery to most Asian addresses within 5-9 business days

Disclaimer:
All orders received before 5 PM U.K time would start printing from the next business day. So the estimated delivery times start from the next day as well. Orders received after 5 PM U.K time (in our internal systems) on a business day or anytime on the weekend will begin printing the second to next business day. For example, an order placed at 11 AM today will begin printing tomorrow, whereas an order placed at 9 PM tonight will begin printing the day after tomorrow.

Unfortunately, due to several restrictions, we are unable to ship to the following countries:

Afghanistan
American Samoa
Belarus
Brunei Darussalam
Central African Republic
The Democratic Republic of Congo
Eritrea
Guinea-bissau
Iran
Lebanon
Libiya Arab Jamahriya
Somalia
Sudan
Russian Federation
Syrian Arab Republic
Ukraine
Venezuela

What is custom duty/charge?

Customs duty are charges levied on goods when they cross international borders. It is a tax that is imposed on imported goods. These duties are charged by special authorities and bodies created by local governments and are meant to protect local industries, economies, and businesses.

Do I have to pay customs charges for the print book order?

The orders shipped to the countries that are listed under EU27 will not bear custom charges. They are paid by Packt as part of the order.

List of EU27 countries: www.gov.uk/eu-eea:

A custom duty or localized taxes may be applicable on the shipment and would be charged by the recipient country outside of the EU27 which should be paid by the customer and these duties are not included in the shipping charges been charged on the order.

How do I know my custom duty charges?

The amount of duty payable varies greatly depending on the imported goods, the country of origin and several other factors like the total invoice amount or dimensions like weight, and other such criteria applicable in your country.

For example:

If you live in Mexico, and the declared value of your ordered items is over $ 50, for you to receive a package, you will have to pay additional import tax of 19% which will be $ 9.50 to the courier service.
Whereas if you live in Turkey, and the declared value of your ordered items is over € 22, for you to receive a package, you will have to pay additional import tax of 18% which will be € 3.96 to the courier service.

How can I cancel my order?

Cancellation Policy for Published Printed Books:

You can cancel any order within 1 hour of placing the order. Simply contact [email protected] with your order details or payment transaction id. If your order has already started the shipment process, we will do our best to stop it. However, if it is already on the way to you then when you receive it, you can contact us at [email protected] using the returns and refund process.

Please understand that Packt Publishing cannot provide refunds or cancel any order except for the cases described in our Return Policy (i.e. Packt Publishing agrees to replace your printed book because it arrives damaged or material defect in book), Packt Publishing will not accept returns.

What is your returns and refunds policy?

Return Policy:

We want you to be happy with your purchase from Packtpub.com. We will not hassle you with returning print books to us. If the print book you receive from us is incorrect, damaged, doesn't work or is unacceptably late, please contact Customer Relations Team on [email protected] with the order number and issue details as explained below:

If you ordered (eBook, Video or Print Book) incorrectly or accidentally, please contact Customer Relations Team on [email protected] within one hour of placing the order and we will replace/refund you the item cost.
Sadly, if your eBook or Video file is faulty or a fault occurs during the eBook or Video being made available to you, i.e. during download then you should contact Customer Relations Team within 14 days of purchase on [email protected] who will be able to resolve this issue for you.
You will have a choice of replacement or refund of the problem items.(damaged, defective or incorrect)
Once Customer Care Team confirms that you will be refunded, you should receive the refund within 10 to 12 working days.
If you are only requesting a refund of one book from a multiple order, then we will refund you the appropriate single item.
Where the items were shipped under a free shipping offer, there will be no shipping costs to refund.

On the off chance your printed book arrives damaged, with book material defect, contact our Customer Relation Team on [email protected] within 14 days of receipt of the book with appropriate evidence of damage and we will work with you to secure a replacement copy, if necessary. Please note that each printed book you order from us is individually made by Packt's professional book-printing partner which is on a print-on-demand basis.

What tax is charged?

Currently, no tax is charged on the purchase of any print book (subject to change based on the laws and regulations). A localized VAT fee is charged only to our European and UK customers on eBooks, Video and subscriptions that they buy. GST is charged to Indian customers for eBooks and video purchases.

What payment methods can I use?

You can pay with the following card types:

Visa Debit
Visa Credit
MasterCard
PayPal

What is the delivery time and cost of print books?

Shipping Details

USA:

Economy: Delivery to most addresses in the US within 10-15 business days

Premium: Trackable Delivery to most addresses in the US within 3-8 business days

UK:

Economy: Delivery to most addresses in the U.K. within 7-9 business days.
Shipments are not trackable

Premium: Trackable delivery to most addresses in the U.K. within 3-4 business days!
Add one extra business day for deliveries to Northern Ireland and Scottish Highlands and islands

EU:

Premium: Trackable delivery to most EU destinations within 4-9 business days.

Australia:

India:

Premium: Delivery to most Indian addresses within 5-6 business days

Rest of the World:

Premium: Countries in the American continent: Trackable delivery to most countries within 4-7 business days

Asia:

Premium: Delivery to most Asian addresses within 5-9 business days

Unfortunately, due to several restrictions, we are unable to ship to the following countries:

Afghanistan
American Samoa
Belarus
Brunei Darussalam
Central African Republic
The Democratic Republic of Congo
Eritrea
Guinea-bissau
Iran
Lebanon
Libiya Arab Jamahriya
Somalia
Sudan
Russian Federation
Syrian Arab Republic
Ukraine
Venezuela

DreamWeaver Aug 20, 2017

Finally a book that gives you the meat and bones of scripting! An easy and practical read for those who are looking for no nonsense scripting knowledge. Worth every dollar!

Amazon Verified review

Charles Smiles Jan 20, 2020

First of all, i've probably purchased 10 bad books on amazon and only left one bad review. Even when they are bad i respect the time an author puts in preparing a book. The author of this book simply does not deserve this kind of respect. Never mind this is a 200 page book, very little effort was put forth to ensure the material was comprehensive and gave readers depth in the material. I actually know how to shell script and have been doing it for my job for years. I purchased this book as a refresher. This author made no effort to explain much of the concepts. I stopped after the first chapter. Granted i understood all 6 basic scripts, but if i had little to no experience i would be completely lost. Can't believe on page 7 he actually typed "The meaning of the remaining lines can be determined by the script itself..." WTF?? No...you explain those lines in your script. That's your job.Like seriously? I actually looked at the intended audience section of the book and made no mention that you had to be an experienced scripter so i really feel for newbies that hit this point only 7 pages into the book and you are lost. I further glanced at other pages in the book and noticed that reoccuring pattern of "here is my script...you figure it out".I've produced technical documentation for mentees at work and under no way would i do this to them.This should be no surprise. Packt publishing has a habit of producing some of the industries worst technical books. They are of low quality. This book is offensive and should be pulled.

Linux Shell Scripting Bootcamp: The fastest way to learn Linux shell scripting

What do you get with Print?

Linux Shell Scripting Bootcamp

Chapter 2. Working with Variables

Using variables in scripts

Note

Chapter 2 - Script 1

Validating parameters using conditional statements

Chapter 2 - Script 2

Comparison operators for strings

Chapter 2 - Script 3

Environment variables

Summary

Page 1 of 6

Key benefits

Description

Who is this book for?

What you will learn

Product Details

What do you get with Print?

Product Details

Frequently bought together

Table of Contents

Recommendations for you

Customer reviews

People who bought this also bought

About the author

FAQs

Linux Shell Scripting Bootcamp: The fastest way to learn Linux shell scripting

What do you get with Print?

Contact Details

Shipping Address

Billing Address

Chapter 2 - Script 1

Key benefits

Description

Who is this book for?

What you will learn

Product Details

What do you get with Print?

Contact Details

Shipping Address

Billing Address

Product Details

Packt Subscriptions

Frequently bought together

Table of Contents

Recommendations for you

Customer reviews

People who bought this also bought

About the author

FAQs