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.

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Table of Contents (19 chapters)
Linux Shell Scripting Bootcamp
Linux Shell Scripting Bootcamp
Credits
Credits
About the Author
About the Author
Acknowledgement
Acknowledgement
About the Reviewer
About the Reviewer
www.PacktPub.com
www.PacktPub.com
Customer Feedback
Customer Feedback
Preface
Preface
Free Chapter
1
Getting Started with Shell Scripting
Getting Started with Shell Scripting
Getting started
Demonstrating the use of scripts
Summary
2
Working with Variables
Working with Variables
Using variables in scripts
Validating parameters using conditional statements
Comparison operators for strings
Environment variables
Summary
3
Using Loops and the sleep Command
Using Loops and the sleep Command
Using loops
Screen manipulation
Indenting your code
Using the for statement
Leaving a loop early
The sleep command
Watching a process
Creating numbered backup files
Summary
4
Creating and Calling Subroutines
Creating and Calling Subroutines
Clearing the screen
File redirection
Command piping
Subroutines
Using parameters
Making a current backup of your work
Summary
5
Creating Interactive Scripts
Creating Interactive Scripts
Chapter 5 - Script 1
Summary
6
Automating Tasks with Scripts
Automating Tasks with Scripts
Chapter 6 - Script 1
Summary
7
Working with Files
Working with Files
Writing files
Reading files
Reading and writing files
Reading and writing files interactively
File checksums
File encryption
Summary
8
Working with wget and curl
Working with wget and curl
Introducing the wget program
wget and recursion
wget options
curl
Summary
9
Debugging Scripts
Debugging Scripts
Syntax errors
Automatic backups
More syntax errors
Logic errors
Using set to debug scripts
Summary
10
Scripting Best Practices
Scripting Best Practices
Verifying backups
ssh and scp
Find and use a good text editor
Environment variables and aliases
ssh prompt
Testing an archive
Progress indicator
Creating new commands from a template
Alerting the user
Summary
Index
Index

Using the for statement

Another way to loop is to use the for statement. It is commonly used when working with files and other lists. The general syntax of a for loop is as follows:

 for variable in list
 do
     some commands
 done

The list can be a collection of strings, or a filename wildcard, and so on. We can take a look at this in the example given in the next section.

Chapter 3 - Script 7

#!/bin/sh
#
# 5/4/2017
#
echo "script7 - Linux Scripting Book"

for i in jkl.c bob Linux "Hello there" 1 2 3
do
 echo -n "$i "
done

for i in script*             # returns the scripts in this directory
do
 echo $i
done

echo "End of script7"
exit 0

And the output on my system. This is my chap3 directory:

The next script shows how the for statement can be used with files:

Chapter 3 - Script 8

#!/bin/sh
#
# 5/3/2017
#
echo "script8 - Linux Scripting Book"

if [ $# -eq 0 ] ; then
 echo "Please enter at least 1 parameter."
 exit 255
fi

for i in $*                  # the "$*" returns every parameter given 
do...
Previous Section
End of Section 5
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