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  • Book Overview & Buying Linux Shell Scripting Cookbook, Second Edition
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Linux Shell Scripting Cookbook, Second Edition

Linux Shell Scripting Cookbook, Second Edition - Second Edition

4.3 (9)
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Linux Shell Scripting Cookbook, Second Edition

Linux Shell Scripting Cookbook, Second Edition

4.3 (9)
Buy this Book

Overview of this book

The shell remains one of the most powerful tools on a computer system — yet a large number of users are unaware of how much one can accomplish with it. Using a combination of simple commands, we will see how to solve complex problems in day to day computer usage.Linux Shell Scripting Cookbook, Second Edition will take you through useful real-world recipes designed to make your daily life easy when working with the shell. The book shows the reader how to effectively use the shell to accomplish complex tasks with ease.The book discusses basics of using the shell, general commands and proceeds to show the reader how to use them to perform complex tasks with ease.Starting with the basics of the shell, we will learn simple commands with their usages allowing us to perform operations on files of different kind. The book then proceeds to explain text processing, web interaction and concludes with backups, monitoring and other sysadmin tasks.Linux Shell Scripting Cookbook, Second Edition serves as an excellent guide to solving day to day problems using the shell and few powerful commands together to create solutions.
Table of Contents (16 chapters)
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Linux Shell Scripting Cookbook
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Linux Shell Scripting Cookbook
Credits
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Credits
About the Authors
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About the Authors
About the Reviewers
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About the Reviewers
www.PacktPub.com
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www.PacktPub.com
Preface
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Preface
Lock Free Chapter
1
Shell Something Out
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Shell Something Out
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Introduction
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Printing in the terminal
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Playing with variables and environment variables
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Function to prepend to environment variables
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Math with the shell
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Playing with file descriptors and redirection
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Arrays and associative arrays
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Visiting aliases
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Grabbing information about the terminal
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Getting and setting dates and delays
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Debugging the script
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Functions and arguments
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Reading the output of a sequence of commands in a variable
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Reading n characters without pressing the return key
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Running a command until it succeeds
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Field separators and iterators
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Comparisons and tests
2
Have a Good Command
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Have a Good Command
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Introduction
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Concatenating with cat
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Recording and playing back of terminal sessions
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Finding files and file listing
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Playing with xargs
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Translating with tr
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Checksum and verification
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Cryptographic tools and hashes
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Sorting unique and duplicates
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Temporary file naming and random numbers
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Splitting files and data
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Slicing filenames based on extension
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Renaming and moving files in bulk
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Spell checking and dictionary manipulation
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Automating interactive input
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Making commands quicker by running parallel processes
3
File In, File Out
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File In, File Out
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Introduction
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Generating files of any size
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The intersection and set difference (A-B) on text files
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Finding and deleting duplicate files
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Working with file permissions, ownership, and the sticky bit
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Making files immutable
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Generating blank files in bulk
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Finding symbolic links and their targets
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Enumerating file type statistics
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Using loopback files
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Creating ISO files and hybrid ISO
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Finding the difference between files, patching
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Using head and tail for printing the last or first 10 lines
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Listing only directories – alternative methods
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Fast command-line navigation using pushd and popd
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Counting the number of lines, words, and characters in a file
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Printing the directory tree
4
Texting and Driving
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Texting and Driving
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Introduction
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Using regular expressions
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Searching and mining a text inside a file with grep
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Cutting a file column-wise with cut
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Using sed to perform text replacement
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Using awk for advanced text processing
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Finding the frequency of words used in a given file
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Compressing or decompressing JavaScript
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Merging multiple files as columns
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Printing the nth word or column in a file or line
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Printing text between line numbers or patterns
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Printing lines in the reverse order
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Parsing e-mail addresses and URLs from text
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Removing a sentence in a file containing a word
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Replacing a pattern with text in all the files in a directory
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Text slicing and parameter operations
5
Tangled Web? Not At All!
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Tangled Web? Not At All!
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Introduction
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Downloading from a web page
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Downloading a web page as plain text
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A primer on cURL
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Accessing Gmail e-mails from the command line
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Parsing data from a website
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Image crawler and downloader
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Web photo album generator
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Twitter command-line client
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Creating a "define" utility by using the Web backend
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Finding broken links in a website
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Tracking changes to a website
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Posting to a web page and reading the response
6
The Backup Plan
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The Backup Plan
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Introduction
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Archiving with tar
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Archiving with cpio
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Compressing data with gzip
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Archiving and compressing with zip
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Faster archiving with pbzip2
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Creating filesystems with compression
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Backup snapshots with rsync
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Version control-based backup with Git
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Creating entire disk images using fsarchiver
7
The Old-boy Network
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The Old-boy Network
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Introduction
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Setting up the network
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Let us ping!
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Listing all the machines alive on a network
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Running commands on a remote host with SSH
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Transferring files through the network
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Connecting to a wireless network
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Password-less auto-login with SSH
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Port forwarding using SSH
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Mounting a remote drive at a local mount point
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Network traffic and port analysis
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Creating arbitrary sockets
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Sharing an Internet connection
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Basic firewall using iptables
8
Put on the Monitor's Cap
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Put on the Monitor's Cap
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Introduction
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Monitoring disk usage
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Calculating the execution time for a command
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Collecting information about logged in users, boot logs, and boot failures
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Listing the top 10 CPU consuming processes in an hour
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Monitoring command outputs with watch
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Logging access to files and directories
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Logfile management with logrotate
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Logging with syslog
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Monitoring user logins to find intruders
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Remote disk usage health monitor
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Finding out active user hours on a system
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Measuring and optimizing power usage
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Monitoring disk activity
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Checking disks and filesystems for errors
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Administration Calls
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Administration Calls
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Introduction
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Gathering information about processes
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Killing processes and send or respond to signals
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Sending messages to user terminals
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Gathering system information
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Using /proc for gathering information
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Scheduling with cron
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Writing and reading the MySQL database from Bash
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User administration script
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Bulk image resizing and format conversion
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Taking screenshots from the terminal
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Managing multiple terminals from one
1
Index
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Index

Calculating the execution time for a command

While testing an application's efficiency or comparing different algorithms to solve a given problem, the execution time taken is very critical. A good algorithm should execute in a minimum amount of time. Let's see how to calculate the execution time.

How to do it...

  1. To measure the execution time, just prefix time to the command you want to run.

    For example:

    $ time COMMAND

    The command will execute and its output will be shown. Along with the output, the time command appends the time taken in stderr. An example is as follows:

    $ time ls
test.txt
next.txt
real    0m0.008s
user    0m0.001s
sys     0m0.003s

    It will show real, user, and system times for execution.

    Note

    An executable binary of the time command is available at /usr/bin/time, as well as a shell built-in named time exists. When we run time, it calls the shell built-in by default. The shell built-in time has limited options. Hence, we should use an absolute path for the executable (/usr/bin...

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Tech Concepts
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Programming languages
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Linux Shell Scripting Cookbook, Second Edition
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