Name: Learning Linux Shell Scripting
Author: Ganesh Naik
ISBN: 9781788991537

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Learning Linux Shell Scripting

Ganesh Naik

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Dedication
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Contributors
About the author
About the reviewer
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Preface
Who this book is for
What this book covers
To get the most out of this book
Download the example code files
Conventions used
Get in touch
Reviews
Getting Started and Working with Shell Scripting
Comparison of shells
Tasks done by the shell
Working in the shell
Learning basic Linux commands
Our first script – Hello World
Compiler and interpreter – differences in process
When not to use scripts
Various directories
Working more effectively with Shell – basic commands
Working with permissions
Changing file permissions
The chmod command
Technique one – the symbolic method
Technique two – the numeric method
Setting umask
Setuid
Setgid
Sticky bit
Summary
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
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
The sort command
IO redirection
File descriptors
Redirection
Brace expansion
Pattern matching with the vi editor
Pattern searching using grep
Summary
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
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
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 a 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 the read command on a 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 the set command
The vi editor setting for debugging
Good practices for Shell scripts
Summary
Performing Arithmetic Operations in Shell Scripts
Using a declare command 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
Floating-point arithmetic
Summary
Automating Decision-Making in Scripts
Checking the exit status of commands
Understanding the test command
Using the test command
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 exit command 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
Summary
Automating Repetitive Tasks
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
Working with Functions
Understanding functions
Displaying functions
Removing functions
Passing arguments or parameters to functions
Sharing the data with 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
Using Advanced Functionality in Scripts
Understanding signals and traps
Using the trap command
Ignoring signals
Resetting signals
Listing traps
Using traps inside a 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 checklist box (checklist)
The menu box (menu)
The radiolist box (radiolist)
The progress meter box (gauge)
Summary
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
System-wide setting scripts
User level settings – default files
Summary
Pattern Matching and Regular Expressions with sed and awk
The basics of regular expressions
sed – non-interactive 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
Taking Backup and Embedding Other Languages in Shell Scripts
Backup of files from command line
Backup command rsync
Backup across the network
Automating backup activity
Embedding other language codes or scripts in Bash shell scripts
Embedding other language code in Bash shell script
Sending output to Bash Script
Storing other language output to Bash variable
Sending data to an embedded language code
Using data from file by embedded language
Sending user input to the embedded code
Embedding Python code in Bash shell Script
Embedding Ruby code
Embedding other language code in Bash – comparative study
A summary of commands for embedding other programming languages
Summary
Database Administration Using Shell Scripts
Introduction to database administration
Working with a MySQL Database
Checking the version of MySQL database
Creating a database
Show databases
Creating a user
Creating a table in MySQL
Inserting data into table
Retrieving data from the table
Updating data
Deleting data
Altering a table
Describing a table
Drop the table
Drop the database
Working with Oracle Database
Switching to an Oracle user
Creating a user in Oracle SQL command line
The Grant statement
The Define command
Predefined variables
Create user through a shell script
Creating a table
Inserting the data into table
Retrieving data from a table
Update the data
Delete the data
Drop the table
Summary
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Learning Linux Shell Scripting