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

Reading input from files

Now, it may seem that these loops can do a little more than just count down numbers. We may want to read data in from a text file and process each line. The shell built-in read command that we saw earlier in this book can be used to read a file line by line. In this way, we can use a loop to process each line of a file.

To demonstrate some of these functionalities, we will use a file that contains the server addresses. These could be hostnames or IP addresses. In the following example, we will make use of the IP addresses of Google DNS Servers. The following command shows the contents of the servers.txt file:

$cat servers.txt

Using the read command in the condition of the while loop, we can loop as long as we have more lines to read from the file. We specify the input file directly after the done keyword. For each line that we read from the file, we can test if the server is up with the command ping and if the server is responding, we append it to a...