Learning Linux Shell Scripting电子书

Learning Linux Shell Scripting

Table of Contents

Learning Linux Shell Scripting

Credits

About the Author

Acknowledgments

About the Reviewers

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Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Downloading the color images of this book

Errata

Piracy

Questions

1. Getting Started and Working with Shell Scripting

Comparison of shells

Tasks done by shell

Working in shell

Learning basic Linux commands

Our first script – Hello World

Compiler and interpreter – difference in process

When not to use scripts

Various directories

Working more effectively with shell – basic commands

Working with permissions

Changing file permissions

Command chmod

Technique one – the symbolic method

Technique two – the numeric method

Setting umask

Setuid

Setgid

Sticky bit

Summary

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

Introducing process basics

Monitoring processes using ps

Process management

Process monitoring tools – top, iostat, and vmstat

Understanding "at"

Understanding "crontab"

Summary

3. Using Text Processing and Filters in Your Scripts

Text filtering tools

Head and tail

The diff command

The cut command

The paste command

The join command

The uniq command

The comm command

The tr command

IO redirection

File descriptors

Redirection

Brace expansion

Pattern matching with the vi editor

Pattern searching using grep

Summary

4. Working with Commands

Learning shell interpretation of commands

Checking and disabling shell internal commands

The exit status

Command substitution

Command separators

Command1; command2

Command grouping

Logical operators

Command1 & command2

Command1 && command2

Command1 || command2

Pipes

Summary

5. Exploring Expressions and Variables

Understanding variables

Working with environment variables

The local variable and its scope

Exporting variables

Working with read-only variables

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

Understanding set

Understanding shift

Resetting positional parameters

Understanding getopts

Understanding default parameters

Working with arrays

Creating an array and initializing it

Accessing array values

Summary

6. Neat Tricks with Shell Scripting

Interactive Shell scripts – reading user input

Summarizing the read command with options

The here document and the << operator

The here operator with the sort command

The here operator with the wc command

The utility ed and here operator

A script for sending messages to all logged-in users

Using the << here operator for FTP usage and data transfer

Turning off variable substitution

The here string and the <<< operator

File handling

Introducing file handling

Using exec to assign file descriptor (fd) to file

Understanding the opening, writing, and closing of a file

Understanding reading from a file

Understanding reading and writing to a file

Using command read on file descriptor (fd)

Reading from one file and writing to another file

Displaying the file descriptor information from the /proc folder

File handling – reading line by line

Executing the command and storing the results in a file

Summarizing usage of the exec command

Debugging

Debugging mode – disabling the shell (option -n)

Debugging mode – displaying commands (option -v)

Debugging mode – the tracing execution (option -x)

Summarizing the debugging options for the Bash shell

Using the set command

Summary of debugging options for set command

The vi editor setting for debugging

Good practices for Shell scripts

Summary

7. Performing Arithmetic Operations in Shell Scripts

Using a command declare for arithmetic

Listing integers

Using the let command for arithmetic

Using the expr command for arithmetic

Using an arithmetic expansion

Binary, octal, and hex arithmetic operations

A floating-point arithmetic

Summary

8. Automating Decision Making in Scripts

Checking the exit status of commands

Understanding the test command

Using the test command with single brackets

Using the test command with double brackets

String comparison options for the test command

Numerical comparison operators for the test command

File test options for the test command

File testing binary operators

Logical test operators

Conditional constructs – if else

Numerical handling if constructs

Using the command exit and the ? variable

String handling with the if construct

Checking for null values

File handling with the if command

Multiple test commands and if constructs

The if/elif/else command

The null command

Switching case

Implementing simple menus with select

Looping with the for command

Exiting from the current loop iteration with the continue command

Exiting from a loop with a break

Working with the do while loop

Using until

Piping the output of a loop to a Linux command

Running loops in the background

The IFS and loops

Summary

9. Working with Functions

Understanding functions

Displaying functions

Removing functions

Passing arguments or parameters to functions

Sharing the data by many functions

Declaring local variables in functions

Returning information from functions

Returning a word or string from a function

Running functions in the background

Command source and period (.)

Creating a library of functions

Summary

10. Using Advanced Functionality in Scripts

Understanding signals and traps

Using the trap command

Ignoring signals

Resetting signals

Listing traps

Using traps in function

Running scripts or processes even if the user logs out

Creating dialog boxes with the dialog utility

Creating a message box (msgbox)

Creating a message box (msgbox) with a title

The yes/no box (yesno)

The input box (inputbox)

The textbox (textbox)

A password box

The menu box (menu)

The checklist box (checklist)

The radiolist box (radiolist)

The progress meter box (gauge)

Summary

11. System Startup and Customizing a Linux System

System startup, inittab, and run levels

The kernel startup and init process

Understanding run levels

System initialization boot scripts

User initialization scripts

Systemwide settings scripts

User level settings – default files

Summary

12. Pattern Matching and Regular Expressions with sed and awk

The basics of regular expressions

sed – noninteractive stream editor

Understanding sed

Understanding regular expression usage in sed

Addressing in sed

How to modify a file with sed

Printing – the p command

Deleting – the d command

Substitution – the s command

Range of selected lines: the comma

Multiple edits – the e command

Reading from files – the r command

Writing to files – the w command

Appending – the a command

Inserting – the i command

Changing – the c command

Transform – the y command

Quit – the q command

Holding and getting – the h and g commands

Holding and exchanging – the h and x commands

sed scripting

Using awk

The meaning of awk

Using awk

Input from files

Input from commands

How awk works

awk commands from within a file

Records and fields

Records

The record separator

The $0 variable

The NR variable

Fields

Field separators

The input field separator

Patterns and actions

Patterns

Actions

Regular expressions

Writing the awk script file

Using variables in awk

Decision making using an if statement

Using the for loop

Using the while loop

Using the do while loop

Summary

Index