Book Image

Linux Shell Scripting Bootcamp

By : James K Lewis
Book Image

Linux Shell Scripting Bootcamp

By: James K Lewis

Overview of this book

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.
Table of Contents (19 chapters)
Linux Shell Scripting Bootcamp
About the Author
About the Reviewer
Customer Feedback

Logic errors

Now let's talk about logic errors. These can be very hard to diagnose, and unfortunately I don't have any magical ways to avoid those. There are some things that can be pointed out however to help track them down.

A common problem with coding is what is called off by 1 errors. This was caused when computer language designers in the sixties decided to number things starting at 0 instead of 1. Computers will happily start counting anywhere you want them to and never complain at all, but most humans tend to do better when they start counting at 1. Most of my peers would probably disagree with this, but since I was the one who always had to fix their off by 1 defects I stand by my comments.

Let's look at the following very simple script:

Chapter 9 - Script 4

# 6/7/2017
echo "Chapter 9 - Script 4"

while [ $x -lt 5 ]
 echo "x: $x"
 let x++

echo "x after loop: $x"
let maxx=x

while [ $y -le 5 ]
 echo "y: $y"
 let y++

echo "y after loop: $y"