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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

Understanding the basics of sed


Having built a little foundation, we can now start to look at some of the operations of sed. The commands will be supplied with most Linux systems and are core commands.

We will dive directly into some simple examples:

$ sed 'p' /etc/passwd

The p operator will print the matched pattern. In this case, we have not specified a pattern so we will match everything. Printing the matched lines without suppressing STDOUT will duplicate lines. The result of this operation is to print all the lines in the passwd file twice. To suppress STDOUT, we use the -n option:

$ sed -n 'p' /etc/passwd

Brilliant!!We have just reinvented the cat command. We can now specifically work with just a range of lines:

$ sed -n '1,3 p ' /etc/passwd

Now we have reinvented the head command, but we can also specify the range in an RE to recreate the grep command:

$ sed -n '/^root/ p' /etc/passwd

We can see this demonstrated in the following screenshot:

Substituting command

We have seen the p command...

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