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

Working with command line arguments (special variables, set and shift, getopt)


Command line arguments are required for the following reasons:

  • They inform the utility or command as to which file or group of files to process (reading/writing of files)

  • Command line arguments tell the command/utility which option to use

Check the following command line:

student@ubuntu:~$  my_program   arg1  arg2  arg3

If my_command is a bash Shell script, then we can access every command line positional parameters inside the script as follows:

$0 would contain "my_program"    # Command
$1 would contain "arg1"      # First parameter
$2 would contain "arg2"      # Second parameter
$3 would contain "arg3"      # Third parameter

The following is the summary of positional parameters:

$0

Shell script name or command

$1–$9

Positional parameters 1–9

${10}

Positional parameter 10

$#

Total number of parameters

$*

Evaluates to all the positional parameters

$@

Same as $*, except when double quoted

"$*"

Displays...