Search icon CANCEL
Subscription
0
Cart icon
Your Cart (0 item)
Close icon
You have no products in your basket yet
Arrow left icon
Explore Products
Best Sellers
New Releases
Books
Videos
Audiobooks
Learning Hub
Free Learning
Arrow right icon
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

eBook
$29.99 $43.99
Paperback
$54.99
Subscription
Free Trial
Renews at $19.99p/m

What do you get with Print?

Product feature icon Instant access to your digital eBook copy whilst your Print order is Shipped
Product feature icon Paperback book shipped to your preferred address
Product feature icon Download this book in EPUB and PDF formats
Product feature icon Access this title in our online reader with advanced features
Product feature icon DRM FREE - Read whenever, wherever and however you want
OR
Modal Close icon
Payment Processing...
tick Completed

Shipping Address

Billing Address

Shipping Methods
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
Estimated delivery fee Deliver to Ukraine

Economy delivery 10 - 13 business days

$6.95

Premium delivery 6 - 9 business days

$21.95
(Includes tracking information)

Product Details

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

What do you get with Print?

Product feature icon Instant access to your digital eBook copy whilst your Print order is Shipped
Product feature icon Paperback book shipped to your preferred address
Product feature icon Download this book in EPUB and PDF formats
Product feature icon Access this title in our online reader with advanced features
Product feature icon DRM FREE - Read whenever, wherever and however you want
OR
Modal Close icon
Payment Processing...
tick Completed

Shipping Address

Billing Address

Shipping Methods
Estimated delivery fee Deliver to Ukraine

Economy delivery 10 - 13 business days

$6.95

Premium delivery 6 - 9 business days

$21.95
(Includes tracking information)

Product Details

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

Packt Subscriptions

See our plans and pricing
Modal Close icon
$19.99 billed monthly
Feature tick icon Unlimited access to Packt's library of 7,000+ practical books and videos
Feature tick icon Constantly refreshed with 50+ new titles a month
Feature tick icon Exclusive Early access to books as they're written
Feature tick icon Solve problems while you work with advanced search and reference features
Feature tick icon Offline reading on the mobile app
Feature tick icon Simple pricing, no contract
$199.99 billed annually
Feature tick icon Unlimited access to Packt's library of 7,000+ practical books and videos
Feature tick icon Constantly refreshed with 50+ new titles a month
Feature tick icon Exclusive Early access to books as they're written
Feature tick icon Solve problems while you work with advanced search and reference features
Feature tick icon Offline reading on the mobile app
Feature tick icon Choose a DRM-free eBook or Video every month to keep
Feature tick icon PLUS own as many other DRM-free eBooks or Videos as you like for just $5 each
Feature tick icon Exclusive print discounts
$279.99 billed in 18 months
Feature tick icon Unlimited access to Packt's library of 7,000+ practical books and videos
Feature tick icon Constantly refreshed with 50+ new titles a month
Feature tick icon Exclusive Early access to books as they're written
Feature tick icon Solve problems while you work with advanced search and reference features
Feature tick icon Offline reading on the mobile app
Feature tick icon Choose a DRM-free eBook or Video every month to keep
Feature tick icon PLUS own as many other DRM-free eBooks or Videos as you like for just $5 each
Feature tick icon Exclusive print discounts

Frequently bought together


Stars icon
Total $ 148.97
Learning Linux Shell Scripting
$54.99
Mastering Linux Shell Scripting
$38.99
Mastering Linux Network Administration
$54.99
Total $ 148.97 Stars icon
Banner background image

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
Get free access to Packt library with over 7500+ books and video courses for 7 days!
Start Free Trial

FAQs

What is the delivery time and cost of print book? Chevron down icon Chevron up icon

Shipping Details

USA:

'

Economy: Delivery to most addresses in the US within 10-15 business days

Premium: Trackable Delivery to most addresses in the US within 3-8 business days

UK:

Economy: Delivery to most addresses in the U.K. within 7-9 business days.
Shipments are not trackable

Premium: Trackable delivery to most addresses in the U.K. within 3-4 business days!
Add one extra business day for deliveries to Northern Ireland and Scottish Highlands and islands

EU:

Premium: Trackable delivery to most EU destinations within 4-9 business days.

Australia:

Economy: Can deliver to P. O. Boxes and private residences.
Trackable service with delivery to addresses in Australia only.
Delivery time ranges from 7-9 business days for VIC and 8-10 business days for Interstate metro
Delivery time is up to 15 business days for remote areas of WA, NT & QLD.

Premium: Delivery to addresses in Australia only
Trackable delivery to most P. O. Boxes and private residences in Australia within 4-5 days based on the distance to a destination following dispatch.

India:

Premium: Delivery to most Indian addresses within 5-6 business days

Rest of the World:

Premium: Countries in the American continent: Trackable delivery to most countries within 4-7 business days

Asia:

Premium: Delivery to most Asian addresses within 5-9 business days

Disclaimer:
All orders received before 5 PM U.K time would start printing from the next business day. So the estimated delivery times start from the next day as well. Orders received after 5 PM U.K time (in our internal systems) on a business day or anytime on the weekend will begin printing the second to next business day. For example, an order placed at 11 AM today will begin printing tomorrow, whereas an order placed at 9 PM tonight will begin printing the day after tomorrow.


Unfortunately, due to several restrictions, we are unable to ship to the following countries:

  1. Afghanistan
  2. American Samoa
  3. Belarus
  4. Brunei Darussalam
  5. Central African Republic
  6. The Democratic Republic of Congo
  7. Eritrea
  8. Guinea-bissau
  9. Iran
  10. Lebanon
  11. Libiya Arab Jamahriya
  12. Somalia
  13. Sudan
  14. Russian Federation
  15. Syrian Arab Republic
  16. Ukraine
  17. Venezuela
What is custom duty/charge? Chevron down icon Chevron up icon

Customs duty are charges levied on goods when they cross international borders. It is a tax that is imposed on imported goods. These duties are charged by special authorities and bodies created by local governments and are meant to protect local industries, economies, and businesses.

Do I have to pay customs charges for the print book order? Chevron down icon Chevron up icon

The orders shipped to the countries that are listed under EU27 will not bear custom charges. They are paid by Packt as part of the order.

List of EU27 countries: www.gov.uk/eu-eea:

A custom duty or localized taxes may be applicable on the shipment and would be charged by the recipient country outside of the EU27 which should be paid by the customer and these duties are not included in the shipping charges been charged on the order.

How do I know my custom duty charges? Chevron down icon Chevron up icon

The amount of duty payable varies greatly depending on the imported goods, the country of origin and several other factors like the total invoice amount or dimensions like weight, and other such criteria applicable in your country.

For example:

  • If you live in Mexico, and the declared value of your ordered items is over $ 50, for you to receive a package, you will have to pay additional import tax of 19% which will be $ 9.50 to the courier service.
  • Whereas if you live in Turkey, and the declared value of your ordered items is over € 22, for you to receive a package, you will have to pay additional import tax of 18% which will be € 3.96 to the courier service.
How can I cancel my order? Chevron down icon Chevron up icon

Cancellation Policy for Published Printed Books:

You can cancel any order within 1 hour of placing the order. Simply contact [email protected] with your order details or payment transaction id. If your order has already started the shipment process, we will do our best to stop it. However, if it is already on the way to you then when you receive it, you can contact us at [email protected] using the returns and refund process.

Please understand that Packt Publishing cannot provide refunds or cancel any order except for the cases described in our Return Policy (i.e. Packt Publishing agrees to replace your printed book because it arrives damaged or material defect in book), Packt Publishing will not accept returns.

What is your returns and refunds policy? Chevron down icon Chevron up icon

Return Policy:

We want you to be happy with your purchase from Packtpub.com. We will not hassle you with returning print books to us. If the print book you receive from us is incorrect, damaged, doesn't work or is unacceptably late, please contact Customer Relations Team on [email protected] with the order number and issue details as explained below:

  1. If you ordered (eBook, Video or Print Book) incorrectly or accidentally, please contact Customer Relations Team on [email protected] within one hour of placing the order and we will replace/refund you the item cost.
  2. Sadly, if your eBook or Video file is faulty or a fault occurs during the eBook or Video being made available to you, i.e. during download then you should contact Customer Relations Team within 14 days of purchase on [email protected] who will be able to resolve this issue for you.
  3. You will have a choice of replacement or refund of the problem items.(damaged, defective or incorrect)
  4. Once Customer Care Team confirms that you will be refunded, you should receive the refund within 10 to 12 working days.
  5. If you are only requesting a refund of one book from a multiple order, then we will refund you the appropriate single item.
  6. Where the items were shipped under a free shipping offer, there will be no shipping costs to refund.

On the off chance your printed book arrives damaged, with book material defect, contact our Customer Relation Team on [email protected] within 14 days of receipt of the book with appropriate evidence of damage and we will work with you to secure a replacement copy, if necessary. Please note that each printed book you order from us is individually made by Packt's professional book-printing partner which is on a print-on-demand basis.

What tax is charged? Chevron down icon Chevron up icon

Currently, no tax is charged on the purchase of any print book (subject to change based on the laws and regulations). A localized VAT fee is charged only to our European and UK customers on eBooks, Video and subscriptions that they buy. GST is charged to Indian customers for eBooks and video purchases.

What payment methods can I use? Chevron down icon Chevron up icon

You can pay with the following card types:

  1. Visa Debit
  2. Visa Credit
  3. MasterCard
  4. PayPal
What is the delivery time and cost of print books? Chevron down icon Chevron up icon

Shipping Details

USA:

'

Economy: Delivery to most addresses in the US within 10-15 business days

Premium: Trackable Delivery to most addresses in the US within 3-8 business days

UK:

Economy: Delivery to most addresses in the U.K. within 7-9 business days.
Shipments are not trackable

Premium: Trackable delivery to most addresses in the U.K. within 3-4 business days!
Add one extra business day for deliveries to Northern Ireland and Scottish Highlands and islands

EU:

Premium: Trackable delivery to most EU destinations within 4-9 business days.

Australia:

Economy: Can deliver to P. O. Boxes and private residences.
Trackable service with delivery to addresses in Australia only.
Delivery time ranges from 7-9 business days for VIC and 8-10 business days for Interstate metro
Delivery time is up to 15 business days for remote areas of WA, NT & QLD.

Premium: Delivery to addresses in Australia only
Trackable delivery to most P. O. Boxes and private residences in Australia within 4-5 days based on the distance to a destination following dispatch.

India:

Premium: Delivery to most Indian addresses within 5-6 business days

Rest of the World:

Premium: Countries in the American continent: Trackable delivery to most countries within 4-7 business days

Asia:

Premium: Delivery to most Asian addresses within 5-9 business days

Disclaimer:
All orders received before 5 PM U.K time would start printing from the next business day. So the estimated delivery times start from the next day as well. Orders received after 5 PM U.K time (in our internal systems) on a business day or anytime on the weekend will begin printing the second to next business day. For example, an order placed at 11 AM today will begin printing tomorrow, whereas an order placed at 9 PM tonight will begin printing the day after tomorrow.


Unfortunately, due to several restrictions, we are unable to ship to the following countries:

  1. Afghanistan
  2. American Samoa
  3. Belarus
  4. Brunei Darussalam
  5. Central African Republic
  6. The Democratic Republic of Congo
  7. Eritrea
  8. Guinea-bissau
  9. Iran
  10. Lebanon
  11. Libiya Arab Jamahriya
  12. Somalia
  13. Sudan
  14. Russian Federation
  15. Syrian Arab Republic
  16. Ukraine
  17. Venezuela