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  • Book Overview & Buying Mastering Linux Shell Scripting
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Mastering Linux Shell Scripting

Mastering Linux Shell Scripting

By : Andrew Mallett
4.3 (10)
Buy this Book
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Mastering Linux Shell Scripting

Mastering Linux Shell Scripting

4.3 (10)
By: Andrew Mallett
Buy this Book

Overview of this book

Shell scripting is a quick method to prototype a complex application or a problem by automating tasks when working on Linux-based systems. Using both simple one-line commands and command sequences complex problems can be solved with ease, from text processing to backing up sysadmin tools. In this book, you’ll discover everything you need to know to master shell scripting and make informed choices about the elements you employ. Get to grips with the fundamentals of creating and running a script in normal mode, and in debug mode. Learn about various conditional statements' code snippets, and realize the power of repetition and loops in your shell script. Implement functions and edit files using the Stream Editor, script in Perl, program in Python – as well as complete coverage of other scripting languages to ensure you can choose the best tool for your project.
Table of Contents (16 chapters)
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Preface
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Preface
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What this book covers
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What you need for this book
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Who this book is for
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Conventions
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Reader feedback
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Customer support
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1
1. What and Why of Scripting with Bash
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1. What and Why of Scripting with Bash
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Bash vulnerabilities
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The bash command hierarchy
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Preparing text editors for scripting
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Creating and executing scripts
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Debugging your scripts
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Summary
2
2. Creating Interactive Scripts
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2. Creating Interactive Scripts
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Using echo with options
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Basic script using read
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Script comments
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Enhancing scripts with read prompts
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Limiting the number of entered characters
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Controlling the visibility of entered text
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Enhancing learning with simple scripts
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Summary
3
3. Conditions Attached
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3. Conditions Attached
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Simple decision paths using command-line lists
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Verifying user input with lists
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Using the test shell builtin
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Creating conditional statements using if
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Extending if with else
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More conditions with elif
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Using case statements
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Script – building a front-end with grep
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Summary
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4. Creating Code Snippets
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4. Creating Code Snippets
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Abbreviations
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Using code snippets
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Summary
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5. Alternative Syntax
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5. Alternative Syntax
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Recapping test
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Providing parameter defaults
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When in doubt – Quote!
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Advanced test using [[
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Arithmetic operations using ((
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Summary
6
6. Iterating with Loops
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6. Iterating with Loops
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For loops
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Controlling the loop
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Reading input from files
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Creating operator menus
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Summary
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7. Creating Building Blocks with Functions
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7. Creating Building Blocks with Functions
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Introducing functions
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Passing parameters to functions
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Returning values from functions
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Using functions in menus
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Summary
8
8. Introducing sed
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8. Introducing sed
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Using grep to display text
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Using regular expressions
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Understanding the basics of sed
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Summary
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9. Automating Apache Virtual Hosts
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9. Automating Apache Virtual Hosts
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Apache name-based Virtual Hosts
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Automating Virtual Host creation
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Summary
10
10. Awk Fundamentals
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10. Awk Fundamentals
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The history behind awk
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Displaying and filtering content from files
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Formatting output
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Further filtering to display users by UID
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Awk control files
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Summary
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11. Summarizing Logs with Awk
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11. Summarizing Logs with Awk
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The HTTPD log file format
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Displaying data from web logs
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Displaying the highest ranking IP address
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Displaying the browser data
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Working with e-mail logs
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Summary
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12. A Better lastlog with Awk
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12. A Better lastlog with Awk
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Using awk ranges to exclude data
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Conditions based on the number of fields
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Manipulating the awk record separator to report on XML data
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Summary
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13. Using Perl as a Bash Scripting Alternative
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13. Using Perl as a Bash Scripting Alternative
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What is Perl?
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Hello World
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Perl arrays
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Conditional statements in Perl
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Using functions within Perl
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Summary
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14. Using Python as a Bash Scripting Alternative
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14. Using Python as a Bash Scripting Alternative
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What is Python?
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Saying Hello World the Python way
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Pythonic arguments
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Significant whitespace
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Reading user input
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Summary
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Index
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Index

Chapter 7. Creating Building Blocks with Functions

In this chapter, we will dive into the wonderful world of functions. We can look at these as modular building blocks creating powerful and adaptive scripts. By creating functions, we add the code in a single building block isolated from the rest of the script. Focusing on improvements of a single function is a lot easier than trying to improve the script as a single object. Without functions, it is difficult to hone in on problem areas and the code is often repeated, it means that updates need to happen in many locations. Functions are named as blocks of code or scripts within scripts and they can overcome many problems associated with a more complex code.

As we make our way through the chapter, we will cover the following topics:

  • Functions
  • Passing parameters to functions
  • Returning values
  • Menu using functions
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Programming languages
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