Book Image

Learning Linux Shell Scripting

By : Ganesh Sanjiv Naik
Book Image

Learning Linux Shell Scripting

By: Ganesh Sanjiv Naik

Overview of this book

Linux is the one of the most powerful and universally adopted OSes. Shell is a program that gives the user direct interaction with the operating system. Scripts are collections of commands that are stored in a file. The shell can read this file and act on the commands as if they were typed on the keyboard. Shell scripting is used to automate day-to-day administration, and for testing or product development tasks. This book covers Bash, GNU Bourne Again SHell, preparing you to work in the exciting world of Linux shell scripting. We start with an introduction to the Shell environment and explain basic commands used in Shell. Next we move on to check, kill, and control the execution of processes in Linux OS. Further, we teach you about the filter tools available in Linux and explain standard output and standard errors devices. Then we will ensure you understand Shell’s interpretation of commands and get a firmer grasp so you use them in practice. Next, you’ll experience some real-world essentials such as debugging and perform Shell arithmetic fluently. Then you’ll take a step ahead and learn new and advanced topics in Shell scripting, such as starting up a system and customizing a Linux system. Finally, you’ll get to understand the capabilities of scripting and learn about Grep, Stream Editor, and Awk.
Table of Contents (20 chapters)
Learning Linux Shell Scripting
Credits
About the Author
Acknowledgments
About the Reviewers
www.PacktPub.com
Preface
Index

Interactive Shell scripts – reading user input


The read command is a shell built-in command for reading data from a file or keyboard.

The read command receives the input from the keyboard or a file until it receives a newline character. Then, it converts the newline character into a null character:

  1. Read a value and store it in the variable, shown as follows:

    read variable
    echo $variable
    

    This will receive text from the keyboard. The received text will be stored in the variable.

  2. Command read with prompt. Whenever we need to display the prompt with certain text, we use the –p option. The option -p displays the text that is placed after –p on the screen:

    #!/bin/bash
    # following line will print "Enter value: " and then read data
    # The received text will be stored in variable value
    read -p "Enter value :  " value

    Output:

    Enter value : abcd
    
  3. If the variable name is not supplied next to the read command, then the received data or text will be stored in a special built-in variable called REPLY. Let's write...