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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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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

Extending if with else


When a script is required to continue regardless of the result of the if condition, it is often necessary to deal with both conditions of the evaluation. What to do when it is true, as well as, false. This is where we can make use of the else keyword. This allows the execution of one block of code when the condition is true and another when the condition is evaluated as false. The pseudo-code for this is shown in the next illustration:

If we consider extending the hello5.sh script that we created earlier, it is easily possible to allow for correct execution regardless of the parameter being present or not. We can recreate this as hello6.sh, as follows:

#!/bin/bash
# Welcome script to display a message to users
# Author: @theurbanpenguin
# Date: 1/1/1971
if [ $# -lt 1 ] ; then
read -p "Enter a name: "
name=$REPLY
else
name=$1
fi
echo "Hello $name"
exit 0

The script sets a named variable now, it helps readability and we can assign the correct value to $name from the input...

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