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

Writing files

We showed in some of the previous chapters how to create and write files by using the redirection operator. To recap, this command will create the file ifconfig.txt (or overwrite the file if it already exists):

  ifconfig  >  ifconfig.txt

The following command will append to any previous file or create a new one if it does not already exist:

  ifconfig  >>  ifconfig.txt

Some of the previous scripts used the back-tick operator to retrieve the data from a file. Let's recap by looking at Script 1:

Chapter 7 - Script 1

# 6/1/2017
echo "Chapter 7 - Script 1"
rm $FN 2> /dev/null          # remove it silently if it exists
while [ $x -le 10 ]          # 10 lines
 echo "x: $x"
 echo "Line $x" >> $FN       # append to file
 let x++
echo "End of script1"
exit 0

Here is a screenshot:

This is pretty straight forward. It removes the file (silently) if it exists, and then outputs each line to the file, incrementing x each time. When x gets...