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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

For loops

All our looping controls can be simple and we will begin by looking at for loops. The word for is a keyword in bash and in working it is similar to if. We can use the command type to verify this, as shown in the following example:

$ type for
for is a shell keyword

As a reserved shell keyword, we can use a for loop both in scripts and directly at the command line. In this way, we can utilize loops within and without the scripts optimizing the use of the command line. A simple for loop is shown in the following example code:

# for u in bob joe ; do
useradd $u
echo '$u:Password1' | chpasswd
passwd -e $u
done

Within a for loop, we read from the list on the right to populate the variable parameter on the left, in this case we will read from the list containing bob and joe into the parameter variable u. Each item from the list is inserted into the variable, one item at a time. In this way, as long as there are items to be processed in the list, the loop will execute until the...

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