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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

Conditions based on the number of fields

If a user logs onto the server's physical console directly rather than logging on through a remote or graphical pseudo-terminal, then the lastlog output will not display the host field. To demonstrate this, I have logged onto my CentOS host directly to the tty1 console and avoided the GUI. The output from the previous awk control file shows that we now have the users tux and bob; bob though is lacking the host field as he is connected to a console.

Conditions based on the number of fields

Although in itself it's not an issue but it will be if we want to filter the fields and the two row's field numbers will vary where a field is omitted from some lines. For lastlog we will have 9 fields for most connections and only 8 fields for those that connect directly to the server console. The desire for the application is that we print the username and the date, but not the time of the last login. We will also print our own header in the BEGIN block. To ensure that we use the correct...

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