Book Image

Learning Linux Shell Scripting - Second Edition

By : Ganesh Sanjiv Naik
Book Image

Learning Linux Shell Scripting - Second Edition

By: Ganesh Sanjiv Naik

Overview of this book

Linux is the most powerful and universally adopted OS. 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 reads this file and acts on commands as if they were typed on the keyboard. Learning Linux Shell Scripting covers Bash, GNU Bourne Again Shell, preparing you to work in the exciting world of Linux shell scripting. CentOS is a popular rpm-based stable and secured Linux distribution. Therefore, we have used CentOS distribution instead of Ubuntu distribution. Linux Shell Scripting is independent of Linux distributions, but we have covered both types of distros. We start with an introduction to the Shell environment and basic commands used. Next, we explore process management in Linux OS, real-world essentials such as debugging and perform Shell arithmetic fluently. You'll then take a step ahead and learn new and advanced topics in Shell scripting, such as decision making, starting up a system, and customizing a Linux environment. You will also learn about grep, stream editor, and AWK, which are very powerful text filters and editors. Finally, you'll get to grips with taking backup, using other language scripts in Shell Scripts as well as automating database administration tasks for MySQL and Oracle. By the end of this book, you will be able to confidently use your own shell scripts in the real world.
Table of Contents (17 chapters)

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 making a backup 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 by 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...