Book Image

Bash Cookbook

By : Ron Brash, Ganesh Sanjiv Naik
Book Image

Bash Cookbook

By: Ron Brash, Ganesh Sanjiv Naik

Overview of this book

In Linux, one of the most commonly used and most powerful tools is the Bash shell. With its collection of engaging recipes, Bash Cookbook takes you through a series of exercises designed to teach you how to effectively use the Bash shell in order to create and execute your own scripts. The book starts by introducing you to the basics of using the Bash shell, also teaching you the fundamentals of generating any input from a command. With the help of a number of exercises, you will get to grips with the automation of daily tasks for sysadmins and power users. Once you have a hands-on understanding of the subject, you will move on to exploring more advanced projects that can solve real-world problems comprehensively on a Linux system. In addition to this, you will discover projects such as creating an application with a menu, beginning scripts on startup, parsing and displaying human-readable information, and executing remote commands with authentication using self-generated Secure Shell (SSH) keys. By the end of this book, you will have gained significant experience of solving real-world problems, from automating routine tasks to managing your systems and creating your own scripts.
Table of Contents (15 chapters)
Title Page
Copyright and Credits
Packt Upsell
Contributors
Preface
Index

Using file attributes with conditional logic


Earlier in this book, we touched upon various tests for strings, numbers, and variables. Using a similar concept built into Bash, we can also use various attributes to test against files and directories. This extends upon the introduction conditional logic to perform tests on files. Does an example exist? Is it a directory? and so on.

For a moment, though, couldn't we just use the results from executing and checking the return code? Absolutely! This is another method you can use, especially if you are using a version of Bash that supports all of Bashes features. It is just another way to "skin the rabbit".

Let's start off first with some of the common flags, which return true if:

  • -e: The file exists
  • -f: This is a regular file and not a directory or device file
  • -s: The file is not empty or zero in size
  • -d: This is a directory
  • -r: This has read permissions
  • -w: This has write permissions
  • -x:This has execute permissions
  • -O: This is the owner of the file the...