Mastering Linux shell scripting a practical guide to Linux command- line, Bash scripting, and Shell programming, 2nd edition

Cover Copyright and Credits Packt Upsell Contributors Table of Contents Preface Chapter 1: The What and Why of Scripting with Bash Technical requirements Types of Linux shells What is bash scripting? The bash command hierarchy Command type Command PATH Preparing text editors for scripting Configuring vim Configuring nano Configuring gedit Creating and executing scripts Hello World! Executing the script Checking the exit status Ensuring a unique name Hello Dolly! Running the script with arguments The importance of correct quotes Printing the script name Declaring variables User-defined variables Environment variables Variable scope Command substitution Debugging your scripts Summary Questions Further reading Chapter 2: Creating Interactive Scripts Technical requirements Using echo with options Basic script using read Script comments Enhancing scripts with read prompts Limiting the number of entered characters Controlling the visibility of the entered text Passing options Passing parameters with options Read options values Try to be standard Enhancing learning with simple scripts Backing-up with scripts Connecting to a server Version 1 – ping Version 2 – SSH Version 3 – MySQL/MariaDB Reading files Summary Questions Further reading Chapter 3: Conditions Attached Technical requirements Simple decision paths using command-line lists Verifying user input with lists Using the test shell built-in Testing strings Testing integers Testing file types Creating conditional statements using if Extending if with else Test command with the if command Checking strings Checking files and directories Checking numbers Combining tests More conditions with elif Creating the backup2.sh using elif Using case statements Recipe – building a frontend with grep Summary Questions Further reading Chapter 4: Creating Code Snippets Technical requirements Abbreviations Using code snippets Bringing color to the Terminal Creating snippets using VS Code Summary Questions Further reading Chapter 5: Alternative Syntax Technical requirement Recapping the test command Testing files Adding logic Square brackets as not seen before Providing parameter defaults Variables Special parameters Setting defaults When in doubt – quote! Advanced tests using [[ White space Other advanced features Pattern matching Regular expressions Regular expression script Arithmetic operations using (( Simple math Parameter manipulation Standard arithmetic tests Summary Questions Further reading Chapter 6: Iterating with Loops Technical requirement for loops Advanced for loops The IFS Counting directories and files C-style for loops Nested loops Redirecting loop output Controlling the loop while loops and until loops Reading input from files Creating operator menus Summary Questions Further reading Chapter 7: Creating Building Blocks with Functions Technical requirements Introducing functions Passing parameters to functions Passing arrays Variable scope Returning values from functions Recursive functions Using functions in menus Summary Questions Further reading Chapter 8: Introducing the Stream Editor Technical requirements Using grep to display text Displaying received data on an interface Displaying user account data Listing the number of CPUs in a system Parsing CSV files The CSV file Isolating catalog entries Understanding the basics of sed The substitute command Global replacement Limiting substitution Editing the file Other sed commands The delete command The insert and append commands The change command The transform command Multiple sed commands Summary Questions Further reading Chapter 9: Automating Apache Virtual Hosts Technical requirements Apache name-based Virtual Hosts Creating the virtual host template First steps Isolating lines sed script files Automating virtual host creation Prompting for data during site creation Summary Questions Further reading Chapter 10: AWK Fundamentals Technical requirements The history behind AWK Displaying and filtering content from files AWK variables User-defined variables Conditional statements The if command while loops for loops Formatting output Further filtering to display users by UID AWK control files Built-in functions Summary Questions Further reading Chapter 11: Regular Expressions Technical requirements Regular expression engines Defining BRE patterns Anchor characters The dot character The character class Ranges of characters Special character classes The asterisk Defining ERE patterns The question mark The plus sign Curly braces The pipe character Expression grouping Using grep Summary Questions Further reading Chapter 12: Summarizing Logs with AWK Technical requirements The HTTPD log file format Displaying data from web logs Selecting entries by date Summarizing 404 errors Summarizing HTTP access codes Resources hits Identify image hotlinking Displaying the highest ranking IP address Displaying the browser data Working with email logs Summary Questions Further reading Chapter 13: A Better lastlog with AWK Technical requirements Using AWK ranges to exclude data The lastlog command Horizontally filtering rows with AWK Counting matched rows Conditions based on the number of fields Manipulating the AWK record separator to report on XML data Apache Virtual Hosts XML catalog Summary Questions Further reading Chapter 14: Using Python as a Bash Scripting Alternative Technical requirements What is Python? Saying Hello World the Python way Pythonic arguments Supplying arguments Counting arguments Significant whitespace Reading user input Using Python to write to files String manipulation Summary Questions Further reading Appendix: Assessments Other Books You May Enjoy Index Master the complexities of Bash shell scripting and unlock the power of shell for your enterprise About This Book • Identify high-level steps such as verifying user input • Using the command line and conditional statements in creating/executing simple shell scripts • Create and edit dynamic shell scripts to manage complex and repetitive tasks • Leverage the command-line to bypass GUI and automate common tasks Who This Book Is For If you are a Linux administrator or a system administrator and are interested in automating tasks in your daily lives, saving time and effort, this book is for you. Basic shell scripting and command-line experience will be required. Familiarity with the tasks you need to automate will be helpful. What You Will Learn • Make, execute, and debug your first Bash script • Create interactive scripts that prompt for user input • Foster menu structures for operators with little command-line experience • Develop scripts that dynamically edit web configuration files to produce a new virtual host • Write scripts that use AWK to search and reports on log files • Draft effective scripts using functions as building blocks, reducing maintenance and build time • Make informed choices by comparing different script languages such as Python with BASH In Detail In this book, you'll discover everything you need to know to master shell scripting and make informed choices about the elements you employ. Grab your favorite editor and start writing your best Bash scripts step by step. 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. You will also learn to write complex shell scripts. This book will also deep dive into file system administration, directories, and system administration like networking, process management, user authentications, and package installation and regular expressions. Towards the end of the book, you will learn how to use Python as a BASH Scripting alternative. By the end of this book, you will know shell scripts at the snap of your fingers and will be able to automate and communicate with your system with keyboard expressions. Style and approach The book will capture your attention and keep you engaged with the simplicity and clarity of each explanation. Every step is accompanied by screenshots so you can cross-check the results before moving on. Master the complexities of Bash shell scripting and unlock the power of shell for your enterprise About This Book Identify high-level steps such as verifying user input Using the command line and conditional statements in creating/executing simple shell scripts Create and edit dynamic shell scripts to manage complex and repetitive tasks Leverage the command-line to bypass GUI and automate common tasks Who This Book Is For If you are a Linux administrator or a system administrator and are interested in automating tasks in your daily lives, saving time and effort, this book is for you. Basic shell scripting and command-line experience will be required. Familiarity with the tasks you need to automate will be helpful. What You Will Learn Make, execute, and debug your first Bash script Create interactive scripts that prompt for user input Foster menu structures for operators with little command-line experience Develop scripts that dynamically edit web configuration files to produce a new virtual host Write scripts that use AWK to search and reports on log files Draft effective scripts using functions as building blocks, reducing maintenance and build time Make informed choices by comparing different script languages such as Python with BASH In Detail In this book, you'll discover everything you need to know to master shell scripting and make informed choices about the elements you employ. Grab your favorite editor and start writing your best Bash scripts step by step. 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. You will also learn to write complex shell scripts. This book will also deep dive into file system administration, directories, and system administration like networking, process management, user authentications, and package installation and regular expressions. Towards the end of the book, you will learn how to use Python as a BASH Scripting alternative. By the end of this book, you will know shell scripts at the snap of your fingers and will be able to automate and communicate with your system with keyboard expressions. Style and approach The book will capture your attention and keep you engaged with the simplicity and clarity of each explanation. Every step is accompanied by screenshots so you can cross-check the results before moving on. Downloading the e.. Master the complexities of Bash shell scripting and unlock the power of shell for your enterpriseKey FeaturesIdentify high-level steps such as verifying user inputUsing the command line and conditional statements in creating/executing simple shell scriptsCreate and edit dynamic shell scripts to manage complex and repetitive tasksLeverage the command-line to bypass GUI and automate common tasksBook DescriptionIn this book, you'll discover everything you need to know to master shell scripting and make informed choices about the elements you employ. Grab your favorite editor and start writing your best Bash scripts step by step. 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. You will also learn to write complex shell scripts. This book will also deep dive into file system administration, directories, and system administration like networking, process management, user authentications, and package installation and regular expressions. Towards the end of the book, you will learn how to use Python as a BASH Scripting alternative. By the end of this book, you will know shell scripts at the snap of your fingers and will be able to automate and communicate with your system with keyboard expressions.What you will learnMake, execute, and debug your first Bash scriptCreate interactive scripts that prompt for user inputFoster menu structures for operators with little command-line experienceDevelop scripts that dynamically edit web configuration files to produce a new virtual hostWrite scripts that use AWK to search and reports on log filesDraft effective scripts using functions as building blocks, reducing maintenance and build timeMake informed choices by comparing different script languages such as Python with BASHWho this book is forIf you are a Linux administrator or a system administrator and are interested in automating tasks in your daily lives, saving time and effort, this book is for you. Basic shell scripting and command-line experience will be required. Familiarity with the tasks you need to automate will be helpful. Shell scripting is a quick method to prototype a complex application or a problem by automating tasks when working on Linux-based systems. This book will make use of both simple one-line commands and command sequences and complex problems can be solved with ease, from text processing to backing up sysadmin tools