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Mastering Linux Shell Scripting

You're reading from   Mastering Linux Shell Scripting Master the complexities of Bash shell scripting and unlock the power of shell for your enterprise

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Product type Paperback
Published in Dec 2015
Publisher
ISBN-13 9781784396978
Length 198 pages
Edition 1st Edition
Tools
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Author (1):
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Andrew Mallett Andrew Mallett
Author Profile Icon Andrew Mallett
Andrew Mallett
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Toc

Table of Contents (16) Chapters Close

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

Verifying user input with lists

In this script, we will ensure that a value has been supplied to the first positional parameter. We can modify the hello2.sh script that we created in Chapter 1, What and Why of Scripting with Bash, to check for user input before displaying the hello text.

You can copy the hello2.sh script to hello4.sh or simply create a new script from scratch. There will not be a lot a typing and the script will be created as $HOME/bin/hello4.sh, as shown:

Verifying user input with lists

We can ensure that the script is executable with the following command:

$ chmod +x $HOME/bin/hello4.sh

We can then run the script with or without arguments. The test statement is looking for the $1 variable to be zero bytes. If it is, then we will not see the hello statement; otherwise it will print the Hello message. In simple terms, we will see the hello message if we supply a name.

The following screenshot shows the output that you will see when you do not supply a parameter to the script, followed by the supplied parameter...

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