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

Running scripts or processes even if the user logs out


Sometimes we may need our script to run even after we log out, such as when taking a back up and similar activities. In this case, even if we log out, the system is powered on and running. In such situations, we can use the nohup command. The nohup command prevents the process from terminating using the SIGHUP signal.

The nohup command makes our script run without attaching it to a terminal. Therefore, if we use the echo command to print text on the terminal. It will not be printed in a terminal, since the script is not attached to a terminal. In such cases, we need to redirect the output to the file, or nohup will automatically redirect the output to a nohup.out file.

Therefore, if we need to run a process, even if we log out, we need to use the nohup command as follows:

$ nohup command &

The example is as follows:

$ nohup sort emp.lst &

This will run a program to sort the emp.lst file in the background.

$ nohup date &