Book Image

Mastering Linux Shell Scripting

By : Andrew Mallett
Book Image

Mastering Linux Shell Scripting

By: Andrew Mallett

Overview of this book

Shell scripting is a quick method to prototype a complex application or a problem by automating tasks when working on Linux-based systems. Using both simple one-line commands and command sequences complex problems can be solved with ease, from text processing to backing up sysadmin tools. In this book, you’ll discover everything you need to know to master shell scripting and make informed choices about the elements you employ. Get to grips with the fundamentals of creating and running a script in normal mode, and in debug mode. Learn about various conditional statements' code snippets, and realize the power of repetition and loops in your shell script. Implement functions and edit files using the Stream Editor, script in Perl, program in Python – as well as complete coverage of other scripting languages to ensure you can choose the best tool for your project.
Table of Contents (21 chapters)
Mastering Linux Shell Scripting
About the Author
About the Reviewer

Arithmetic operations using ((

When using bash and some other advanced shells, we may make use of the (( )) notation to simplify mathematical operations with scripts.

Simple math

The double parenthesis construct in bash allows for arithmetic expansion. Using this in the simplest format, we can easily carry out integer arithmetic. This becomes a replacement for the let built-in. The following examples show the use of the let command and the double parenthesis to achieve the same result:

$ a=(( 2 + 3 ))
$ let a=2+3

In both cases, the a parameter is populated with the sum of 2 + 3.

Parameter manipulation

Perhaps, a little more useful to us in scripting is the C-style parameter manipulation that we can include using the double parenthesis. We can often use this to increment a counter within a loop and also put a limit on the number of times the loop iterates. Consider the following code:

$ (( COUNT++ ))
echo $COUNT

Within this example, we first set COUNT to 1 and then we increment it with...