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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

Recapping test

So far we have used the built-in test command to drive our conditional statements. Using other options with test, we can look at the returned value to determine the status of files in the file system. Running the test without any option will return a false output:

$ test

Testing files

Commonly, we can use test to check the conditions based around files. For example, to test that a file is present, or not, we can use the-e option. The following command will test the existence of the /etc/hosts file:

test -e /etc/hosts

We can run this test again, but this time check that the file not only exists but is a regular file as opposed to having some special purpose. Specific file types can be directories, pipes, links, and so on. The option for a regular file is -f.

$ test -f /etc/hosts

Adding logic

If we need to open a file from within our script, we will test that the file is both a regular file and has the read permission set. To achieve this with test, we can also include the -a option...

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