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Learning Linux Shell Scripting
Learning Linux Shell Scripting

Learning Linux Shell Scripting: Unleash the power of shell scripts to solve real-world problems by breaking through the practice of writing tedious code

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Profile Icon Ganesh Sanjiv Naik
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Full star icon Full star icon Full star icon Full star icon Full star icon 5 (5 Ratings)
Paperback Dec 2015 306 pages 1st Edition
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Arrow left icon
Profile Icon Ganesh Sanjiv Naik
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Full star icon Full star icon Full star icon Full star icon Full star icon 5 (5 Ratings)
Paperback Dec 2015 306 pages 1st Edition
eBook
₱1571.99 ₱2245.99
Paperback
₱2806.99
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₱1571.99 ₱2245.99
Paperback
₱2806.99
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Table of content icon View table of contents Preview book icon Preview Book

Learning Linux Shell Scripting

Chapter 2. Drilling Deep into Process Management, Job Control, and Automation

In the last chapter, we introduced ourselves to the Bash shell environment in Linux. You learned basic commands and wrote your first Shell script as well.

You also learned about process management and job control. This information will be very useful for system administrators in automation and solving many problems.

In this chapter, we will cover the following topics:

  • Monitoring processes with ps
  • Job management—working with fg, bg, jobs, and kill
  • Exploring at and crontab

Introducing process basics

A running instance of a program is called as process. A program stored in the hard disk or pen drive is not a process. When that stored program starts executing, then we say that process has been created and is running.

Let's very briefly understand the Linux operating system boot-up sequence:

  1. In PCs, initially the BIOS chip initializes system hardware, such as PCI bus, display device drivers, and so on.
  2. Then the BIOS executes the boot loader program.
  3. The boot loader program then copies kernel in memory, and after basic checks, it calls a kernel function called start_kenel().
  4. The kernel then initiates the OS and creates the first process called init.
  5. You can check the presence of this process with the following command:
    $ ps –ef
    
  6. Every process in the OS has one numerical identification associated with it. It is called a process ID. The process ID of the init process is 1. This process is the parent process of all user space processes.
  7. In the OS, every new...

Monitoring processes using ps

We have used the command ps in the introduction. Let's learn more about it:

  • To list the process associated with our current Bash shell terminal, enter the following command:
    $ ps
    
    Monitoring processes using ps
  • To list processes along with the parent process ID associated with the current terminal, enter the following command:
    $ ps –f
    
    Monitoring processes using ps

    We can see the process ID in the PID column and the parent process ID in the PPID column in the preceding output.

  • To list processes with the parent process ID along with the process state, enter the following command:
    $ ps –lf
    
    Monitoring processes using ps

    In the preceding output, the column with S (state) shows the current state of a process, such as R for running and S for suspended state.

  • To list all the processes running in the operating system including system processes, enter the following command:
    $ ps –ef
    
    Monitoring processes using ps

    The process names in [] are kernel threads. If you are interested in more options to learn about the ps command, you can use the following command:

    $ man ps.
    

    To...

Process management

Since we have understood the command to check processes, we will learn more about managing different processes as follows:

  • In a Bash shell, when we enter any command or start any program, it starts running in foreground. In such a situation, we cannot run more than one command in the foreground. We need to create many terminal windows for starting many processes. If we need to start many processes or programs from the same terminal, then we will need to start them as background processes.
  • If we want to start a process in the background, then we need to append the command in the Bash shell by &.
  • If I want to start my program Hello as the background process, then the command would be as follows:
    $ Hello &
    
  • If we terminate any command by &, then it starts running as the background process.

For example, we will issue a simple sleep command, which creates a new process. This process sleeps for the duration, which is mentioned in the integer value next to the sleep command...

Process monitoring tools – top, iostat, and vmstat

We can view the native performance of various processes in OS using tools which will be discussed further. To view a dynamic real-time view of the top running processes in OS, use the following command:

$top
Process monitoring tools – top, iostat, and vmstat

An explanation of the top command generated output is as follows:

The $top command displays a lot of information about the running system.

The first line of the display is shown as follows:

Process monitoring tools – top, iostat, and vmstat

The description of fields in the first line is as follows:

  • Current time
  • System uptime
  • Number of users logged in
  • Load average of 5, 10, and 15 minutes, respectively

The second line is shown as follows:

Process monitoring tools – top, iostat, and vmstat

This line shows the summary of tasks or processes. It shows the total number of all the processes, which includes the total number of running, sleeping, stopped, and zombie processes.

The third line is shown as follows:

Process monitoring tools – top, iostat, and vmstat

This line shows information about CPU usage in % in different modes as follows:

  • * us (user): CPU usage in % for running (un-niced) the user...

Understanding "at"

Many a times we need to schedule a task for a future time, say in the evening at 8 P.M. on a specific day. We can use the at command in such a situation.

Sometimes we need to repeat the same task at a specific time, periodically, every day, or every month. In such situations, we can use the crontab command.

Let's learn more about the utility of the at command. To use the at command, the syntax is as follows:

$ at time date

The following are the examples of the at command:

  • The Control + D command will save the at job. The task will be executed at 11.15 A.M. This command will log messages to the log.txt file at 11.15 A.M.:
    $ at 11.15 AM
    at >  echo "Hello World" > $HOME/log.txt
    at >  Control + D
    
  • The following command will send an e-mail on March 31, 2015 at 10 A.M.:
    $ at 10am mar 31 2015
    at> echo "taxes due" | mail jon
    at> ^D
    
  • The following command will make the task run on May 20 at 11 A.M.:
    $ at 11 am may 20
    
  • All the jobs which...

Introducing process basics


A running instance of a program is called as process. A program stored in the hard disk or pen drive is not a process. When that stored program starts executing, then we say that process has been created and is running.

Let's very briefly understand the Linux operating system boot-up sequence:

  1. In PCs, initially the BIOS chip initializes system hardware, such as PCI bus, display device drivers, and so on.

  2. Then the BIOS executes the boot loader program.

  3. The boot loader program then copies kernel in memory, and after basic checks, it calls a kernel function called start_kenel().

  4. The kernel then initiates the OS and creates the first process called init.

  5. You can check the presence of this process with the following command:

    $ ps –ef
    
  6. Every process in the OS has one numerical identification associated with it. It is called a process ID. The process ID of the init process is 1. This process is the parent process of all user space processes.

  7. In the OS, every new process is created...

Monitoring processes using ps


We have used the command ps in the introduction. Let's learn more about it:

  • To list the process associated with our current Bash shell terminal, enter the following command:

    $ ps
    
  • To list processes along with the parent process ID associated with the current terminal, enter the following command:

    $ ps –f
    

    We can see the process ID in the PID column and the parent process ID in the PPID column in the preceding output.

  • To list processes with the parent process ID along with the process state, enter the following command:

    $ ps –lf
    

    In the preceding output, the column with S (state) shows the current state of a process, such as R for running and S for suspended state.

  • To list all the processes running in the operating system including system processes, enter the following command:

    $ ps –ef
    

    The process names in [] are kernel threads. If you are interested in more options to learn about the ps command, you can use the following command:

    $ man ps.
    

    To find a particular process...

Left arrow icon Right arrow icon

Key benefits

  • Learn how to efficiently and effectively build shell scripts and develop advanced applications with this handy book
  • Develop high quality and efficient solutions by writing professional and real-world scripts, and debug scripts by checking and shell tracing
  • A step-by-step tutorial to automate routine tasks by developing scripts from a basic level to very advanced functionality

Description

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.

Who is this book for?

This book is ideal for those who are proficient at working with Linux and who want to learn about shell scripting to improve their efficiency and practical skills. By the end of this book, you will be able to confidently use your own shell scripts in the real world.

What you will learn

  • Familiarize yourself with the various text filtering tools available in Linux
  • Combine the fundamental text and file processing commands to process data and automate repetitive tasks
  • Understand expressions and variables and how to use them practically
  • Automate decision-making and save a lot of time and effort of revisiting code
  • Get to grips with advanced functionality such as using traps and signals and using dialogs to develop screens
  • Start up a system and customize a Linux system
  • Take an in-depth look at regular expressions and pattern matching to understand the capabilities of scripting

Product Details

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Publication date, Length, Edition, Language, ISBN-13
Publication date : Dec 31, 2015
Length: 306 pages
Edition : 1st
Language : English
ISBN-13 : 9781785286216

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Publication date : Dec 31, 2015
Length: 306 pages
Edition : 1st
Language : English
ISBN-13 : 9781785286216

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Table of Contents

13 Chapters
1. Getting Started and Working with Shell Scripting Chevron down icon Chevron up icon
2. Drilling Deep into Process Management, Job Control, and Automation Chevron down icon Chevron up icon
3. Using Text Processing and Filters in Your Scripts Chevron down icon Chevron up icon
4. Working with Commands Chevron down icon Chevron up icon
5. Exploring Expressions and Variables Chevron down icon Chevron up icon
6. Neat Tricks with Shell Scripting Chevron down icon Chevron up icon
7. Performing Arithmetic Operations in Shell Scripts Chevron down icon Chevron up icon
8. Automating Decision Making in Scripts Chevron down icon Chevron up icon
9. Working with Functions Chevron down icon Chevron up icon
10. Using Advanced Functionality in Scripts Chevron down icon Chevron up icon
11. System Startup and Customizing a Linux System Chevron down icon Chevron up icon
12. Pattern Matching and Regular Expressions with sed and awk Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Full star icon Full star icon Full star icon Full star icon 5
(5 Ratings)
5 star 100%
4 star 0%
3 star 0%
2 star 0%
1 star 0%
Andras Pasztirak Feb 02, 2016
Full star icon Full star icon Full star icon Full star icon Full star icon 5
One of the better, more comprehensive guides on the topic of shell scripting I've ever seen. It goes through all the necessary basics and dwells into the more advanced topics but in a way that the pacing is great, easy to follow, not jarring. The chapters are built up logically for the most part, the one tiny gripe I'd have is that regular expressions are only brought up in the very last chapter, I feel they should be featured a lot earlier in the book as they are an integral part of scripts and command line work. Still, I don't think that's enough reason to deprive it of 5 stars.I'd highly recommend this ebook for either a complete beginner in shell scripting or someone who has experience in the field but is looking to refresh their memory, perhaps after not touching the shell after a long time.
Amazon Verified review Amazon
Laurent Jan 06, 2016
Full star icon Full star icon Full star icon Full star icon Full star icon 5
This book is well structured about shell scripting used to manage daily tasks on a Linux computer.Of course it is more for people likes terminal.A very good book to grow up your knowledge of this intimacy with the essential tools of shell.
Amazon Verified review Amazon
Andrea Jan 31, 2016
Full star icon Full star icon Full star icon Full star icon Full star icon 5
For sure is not the only book about shell scripting (books on this topic have started since '70 years), but it's really good and with a step by step approach.You start learning some common Unix commands (included some Unix/Linux concepts), the job control, the text filtering features.With all this basis you start build some scripts using variables, flows, conditions.Several tricks are included and also several examples.Finally it's included also a part to build text based window interface with dialog.Considering that shell scripting is still used (also if languages like Perl, Ptyton, Ruby can totally replace them), this book is really useful for Linux/Unix system administrator and people that need to learn on how programming with shell script language.
Amazon Verified review Amazon
CC Dec 03, 2017
Full star icon Full star icon Full star icon Full star icon Full star icon 5
I LOVE this book!!! Ganesh takes the time to explain and give examples on almost everything. Give it a read and you will not regret it. Thank you to Ganesh and all who have contributed to a totally AWESOME book! Please keep writing!!!
Amazon Verified review Amazon
adnan baloch Jan 15, 2016
Full star icon Full star icon Full star icon Full star icon Full star icon 5
This book is borne out of the author's own experiences over the years solving day to day problems in his work. That should give anyone confidence that the examples in this book are as real-world as they can be. Veterans from the DOS days will fondly remember creating batch files to accomplish a myriad of tasks. If you are one of them and switched to an OS like Unix or Linux, this is the book to get. Everything from file permissions, process management, task scheduling, text processing to interactive shell scripting is covered here. Want to backup a folder in the middle of the night and want its status emailed to you? Check. Have a complex operation in mind involving loops, file handling, arrays, functions and message dialogs? The author arms you with the necessary information to achieve that. The final chapters take the readers through understanding the Linux startup process and customizing the system environment as well as using regular expressions for complex pattern matching. Apart from networking, this book is all you need to handle common Linux system admin duties.
Amazon Verified review Amazon
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