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

James K Lewis

$19.99 per month

3.5 (2 Ratings)

Paperback Jul 2017 208 pages 1st Edition

James K Lewis

$19.99 per month

3.5 (2 Ratings)

Paperback Jul 2017 208 pages 1st Edition

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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...

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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

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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

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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

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Description

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What you will learn

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

What do you get with a Packt Subscription?

Chapter 2 - Script 1

Key benefits

Description

Who is this book for?

What you will learn

Product Details

What do you get with a Packt Subscription?

Product Details

Packt Subscriptions

Frequently bought together

Table of Contents

Recommendations for you

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About the author

FAQs