Book Image

Linux Shell Scripting Essentials

By : Sinny Kumari, Khem Raj
Book Image

Linux Shell Scripting Essentials

By: Sinny Kumari, Khem Raj

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Table of Contents (15 chapters)
Linux Shell Scripting Essentials
Linux Shell Scripting Essentials
Credits
Credits
About the Author
About the Author
About the Reviewers
About the Reviewers
www.PacktPub.com
www.PacktPub.com
Preface
Preface
Free Chapter
1
The Beginning of the Scripting Journey
The Beginning of the Scripting Journey
Hello World in shell
Define variables of choice
Builtin shell variables
Operators
Shell expansions
Construct commands using eval
Make bash behave using set
Summary
2
Getting Hands-on with I/O, Redirection Pipes, and Filters
Getting Hands-on with I/O, Redirection Pipes, and Filters
Standard I/O and error streams
Redirecting the standard I/O and error streams
Pipe and pipelines – connecting commands
Regular expressions
Filtering an output using grep
Editing output using sed
Duplicating a stream using tee
Sorting and finding unique text
Character-based translation using tr
Filtering based on lines—head and tail
The Cut-based selection
Summary
3
Effective Script Writing
Effective Script Writing
Exiting from scripts and exit codes
Testing expressions with a test
Using conditional statements with if and else
Indexed arrays and associative arrays
Looping around with for
The select, while, and until loops
Switch to my choice
Passing stdout as a parameter using xargs
Using functions and positional parameters
Alias
pushd and popd
Summary
4
Modularizing and Debugging
Modularizing and Debugging
Modularizing your scripts
Passing command line parameters to script
Debugging your scripts
Command completion
Summary
5
Customizing the Environment
Customizing the Environment
Knowing the default environment
Modifying a shell environment
Using bash startup files
Knowing your history
Task management
Summary
6
Working with Files
Working with Files
Performing basic file operations
Moving and copying files
Comparing files
Finding files
Links to a file
Special files
Temporary files
Permission and ownership
Getting the list of open files
Configuration files
Summary
7
Welcome to the Processes
Welcome to the Processes
Process management
Listing and monitoring processes
Process substitution
Process scheduling priorities
Signals
Traps
Inter-process communication
Summary
8
Scheduling Tasks and Embedding Languages in Scripts
Scheduling Tasks and Embedding Languages in Scripts
Running tasks at a specific time
Cron jobs
Managing the crontab entry
systemd
Embedding languages
Summary
Index
Index

Listing and monitoring processes

In a running system, we often notice that suddenly a system is responding slowly. This can be because a running application is consuming a lot of memory or a process is doing CPU-intensive work. It's hard to predict which application is causing the system to respond slower. To know the reason, it is good to know what all processes are running and also know the monitoring behavior (such as the amount of CPU or memory being consumed) of processes.

Listing processes

To know a list of processes running in the system, we can use the ps command.

Syntax

The syntax of the ps command is as follows:

ps [option]

There are a lot of options to use the ps command. The commonly used options are explained in the following table.

Simple process selection

The following table shows the multiple options that can be clubbed together and used to get a better selection of results:

Option

Description

-A, -e

Selects all processes

-N

Selects all processes that don't fulfill a condition...

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