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

Using set to debug scripts

You can use the set commands to help with debugging your scripts. There are two common options to set, x and v. Here is a description of each.

Note that a - activates the set while a + deactivates it. If that sounds backwards to you it is because it is backwards.


  • set -x: to display the expanded trace before running the command

  • set -v: to display the input line as it is parsed

Take a look at Script 5 which shows what set -x does:

Chapter 9 - Script 5 and Script 6

# 6/7/2017
set -x                       # turn debugging on

echo "Chapter 9 - Script 5"

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

echo "End of script5"
exit 0

And the output:

If this looks a little strange at first don't worry, it gets easier the more you look at it. In essence, the lines that start with a + are the expanded source code lines, and the lines without a + are the output of the script.

Look at the first two lines. It shows:

 + echo 'Chapter 9 - Script 5'
 Chapter 9...