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Mastering Linux Shell Scripting
Mastering Linux Shell Scripting

Mastering Linux Shell Scripting: Master the complexities of Bash shell scripting and unlock the power of shell for your enterprise

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Mastering Linux Shell Scripting

Chapter 2. Creating Interactive Scripts

In Chapter 1, What and Why of Scripting with Bash, of this book we learned how to create a script and use some of its basics elements. These include optional parameters that we can pass through to the script when it is executed. In this chapter, we will extend this by using the read shell built-in command to allow for interactive scripts. Interactive scripts are scripts that prompt for information during the script execution. In doing so, we will cover the following topics:

  • Using echo with options
  • Basic script using read
  • Adding comments
  • Enhancing read scripts with prompts
  • Limiting the number of entered characters
  • Control the visibility of the entered text
  • Simple scripts to enforce our learning

Using echo with options

So far, in this book we have been able to see that the echo command is very useful and is going to be in many of our scripts, if not all. We have also seen that this is both a built-in command as well as a command file. When running the echo command, the built-in command will be used unless we state the full path to the file. We can test this with the following command:

$ test -a echo

To gain help on the built-in command, we can use man bash and search for echo; however, the echo command is identical to the internal command so I will recommend that you use man echo in most cases in order to display command options.

The basic use of echo that we have seen so far will produce a text output and a new line. This is often the desired response so we don't have to be concerned that the next prompt will append to the end of the echoed text. The new line separates the script output from the next shell prompt. If we do not supply any text string to print, echo will print...

Basic script using read

When used as a part of a script that prompts for user input, the suppression of the line feed is exactly what we want. We will begin by copying the existing hello2.sh script to hello3.sh and build an interactive script. Initially, we will use echo as the prompt mechanism but as we gradually enhance the script, we will generate the prompt directly from the shell built-in read command:

$ cp $HOME/bin/hello2.sh $HOME/bin/hello3.sh
$ chmod +x $HOME/bin/hello3.sh

Edit the $HOME/bin/hello3.sh script so that it reads as the following:

#!/bin/bash
echo -n "Hello I  $(basename $0) may I ask your name: "
read
echo "Hello $REPLY"
exit 0

As we execute the script, we will be greeted and prompted with our own name. This is echoed out using the $REPLY variable in the echo statement. As we have not yet supplied a variable name to the read built-in command the default $REPLY variable is used. The script execution and output is shown in the following screenshot. Take...

Script comments

We should always introduce commenting scripts early in the piece. A script comment is prefaced with a # symbol. Anything after the # symbol is a comment and is not evaluated by the script. The shebang, #!/bin/bash, is primarily a comment and, as such, is not evaluated by the script. The shell running the script reads the shebang so it knows which command interpreter to hand the script over to. A comment may be at the start of a line or partly into the line. Shell scripting does not have the notion of multi-line comments.

If you are not already familiar with comments, then they are added to the script to tell all about who wrote the script, when it was written and last updated, and what the script does. It is the metadata of the script.

The following is an example of comments in scripts:

#!/bin/bash
# Welcome script to display a message to users on login
# Author: @theurbanpenguin
# Date: 1/1/1971

It is a good practice to comment and add comments that explain what the code is...

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Key benefits

  • Identify the high level steps such as verifying user input, using command lines and conditional statements in creating and executing simple shell scripts
  • Create and edit dynamic shell scripts to manage complex and repetitive tasks
  • Learn about scripting in Perl and programming in Python as a BASH scripting alternative with this practical, step-by-step guide

Description

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.

Who is this book for?

Mastering Linux Shell Scripting has been written for Linux administrators who want to automate tasks in their daily lives, saving time and effort. You’ll need to have command-line experience and be familiar with the tasks that you need to automate.

What you will learn

  • Use the type command to identify the order of command evaluation
  • 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 Perl and Python with BASH
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Publication date : Dec 24, 2015
Length: 198 pages
Edition : 1st
Language : English
ISBN-13 : 9781784396978
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Table of Contents

15 Chapters
1. What and Why of Scripting with Bash Chevron down icon Chevron up icon
2. Creating Interactive Scripts Chevron down icon Chevron up icon
3. Conditions Attached Chevron down icon Chevron up icon
4. Creating Code Snippets Chevron down icon Chevron up icon
5. Alternative Syntax Chevron down icon Chevron up icon
6. Iterating with Loops Chevron down icon Chevron up icon
7. Creating Building Blocks with Functions Chevron down icon Chevron up icon
8. Introducing sed Chevron down icon Chevron up icon
9. Automating Apache Virtual Hosts Chevron down icon Chevron up icon
10. Awk Fundamentals Chevron down icon Chevron up icon
11. Summarizing Logs with Awk Chevron down icon Chevron up icon
12. A Better lastlog with Awk Chevron down icon Chevron up icon
13. Using Perl as a Bash Scripting Alternative Chevron down icon Chevron up icon
14. Using Python as a Bash Scripting Alternative Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon

Customer reviews

Top Reviews
Rating distribution
Full star icon Full star icon Full star icon Full star icon Half star icon 4.3
(10 Ratings)
5 star 70%
4 star 10%
3 star 10%
2 star 0%
1 star 10%
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SuJo Feb 27, 2016
Full star icon Full star icon Full star icon Full star icon Full star icon 5
I was extremely skeptical at first glance; however after reading this book it truly covers each topic with enough detail to give a clear understanding of the tasks at hand. Doing a lot of automation work with frameworks like Puppet which can benefit from shell scripts, and all I can say is wow.. you really need to pickup a copy of this book as it is well worth the cost.
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C.P. Feb 26, 2017
Full star icon Full star icon Full star icon Full star icon Full star icon 5
This book so far has been very useful and I am very pleased with the contents so far. I have read about 1/3 and so far an A+ from me.
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Mark Smith Apr 16, 2016
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Great Book and highly recommend.
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Perry Nally Mar 02, 2016
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Almost all you need, and certainly all you need to get you up and running. Gave me the ins and outs of the bash shell as well as pointed me in the right direction with the intro to Peral and Python as additional resources to use when bash shell does allow my to do what I need. I'll have this book as a reference for a very long time when I start building linux embedded devices. I know I'll be turning to this book for references on creating the scripts I need.
Amazon Verified review Amazon
Tim Crothers Mar 10, 2016
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Really, really good coverage of bash scripting core fundamentals. Literally one of the best I've read and I've read many of them. I wouldn't go nearly as far as to say complete as some of the other reviews have stated but it definitely does a really good job of getting you started down the road. The only issue I had in the end is the "mastering" part of the title. I don't think any book under 200 pages should claim to provide mastery of a topic, especially one as complex as bash shell scripting, but in the end I decided not to dock it a start because it does such a good job at what it does cover. My preference would be to drop the small sections on Perl and Python. They are topics worthy of their own treatment and the pages could have been put to better use going deeper on shell scripting.
Amazon Verified review Amazon
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