Linux Shell Scripting Cookbook, Second Edition电子书

Linux Shell Scripting Cookbook

Table of Contents

Linux Shell Scripting Cookbook

Credits

About the Authors

About the Reviewers

www.PacktPub.com

Support files, eBooks, discount offers and more

Why Subscribe?

Free Access for Packt account holders

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Downloading the example code

Errata

Piracy

Questions

1. Shell Something Out

Introduction

Printing in the terminal

How to do it...

How it works...

There's more...

Escaping newline in echo

Printing a colored output

Playing with variables and environment variables

Getting ready

How to do it...

There's more...

Finding the length of a string

Identifying the current shell

Checking for super user

Modifying the Bash prompt string (username@hostname:~$)

Function to prepend to environment variables

How to do it...

How it works...

Math with the shell

Getting ready

How to do it...

Playing with file descriptors and redirection

Getting ready

How to do it...

How it works...

There's more...

Redirection from a file to a command

Redirecting from a text block enclosed within a script

Custom file descriptors

Arrays and associative arrays

Getting ready

How to do it...

There's more...

Defining associative arrays

Listing of array indexes

Visiting aliases

How to do it...

There's more...

Escaping aliases

Grabbing information about the terminal

Getting ready

How to do it...

Getting and setting dates and delays

Getting ready

How to do it...

How it works...

There's more...

Producing delays in a script

Debugging the script

How to do it...

How it works...

There's more...

Shebang hack

Functions and arguments

How to do it...

There's more...

The recursive function

Exporting functions

Reading the return value (status) of a command

Passing arguments to commands

Reading the output of a sequence of commands in a variable

Getting ready

How to do it...

There's more...

Spawning a separate process with subshell

Subshell quoting to preserve spacing and the newline character

Reading n characters without pressing the return key

How to do it...

Running a command until it succeeds

How to do it...

How it works...

There's more...

A faster approach

Adding a delay

Field separators and iterators

Getting ready

How to do it...

Comparisons and tests

How to do it...

2. Have a Good Command

Introduction

Concatenating with cat

How to do it...

How it works…

There's more...

Getting rid of extra blank lines

Displaying tabs as ^I

Line numbers

Recording and playing back of terminal sessions

Getting ready

How to do it...

How it works...

Finding files and file listing

Getting ready

How to do it...

There's more...

Search based on filename or regular expression match

Negating arguments

Search based on the directory depth

Search based on file type

Search on file times

Search based on file size

Deleting based on the file matches

Match based on the file permissions and ownership

Executing commands or actions with find

Skipping specified directories when using the find command

Playing with xargs

Getting ready

How to do it...

How it works…

There's more...

Passing formatted arguments to a command by reading stdin

Using xargs with find

Counting the number of lines of C code in a source code directory

While and subshell trick with stdin

Translating with tr

Getting ready

How to do it...

How it works…

There's more...

Deleting characters using tr

Complementing character set

Squeezing characters with tr

Character classes

Checksum and verification

Getting ready

How to do it...

How it works...

There's more...

Checksum for directories

Cryptographic tools and hashes

How to do it...

Sorting unique and duplicates

Getting ready

How to do it...

How it works…

There's more...

Sorting according to the keys or columns

uniq

Temporary file naming and random numbers

How to do it...

How it works…

Splitting files and data

How to do it...

There's more…

Specifying a filename prefix for the split files

Slicing filenames based on extension

How to do it…

How it works…

Renaming and moving files in bulk

Getting ready

How to do it...

How it works…

Spell checking and dictionary manipulation

How to do it...

How it works...

Automating interactive input

Getting ready

How to do it...

How it works…

There's more...

Automating with expect

Making commands quicker by running parallel processes

How to do it...

How it works...

3. File In, File Out

Introduction

Generating files of any size

How to do it...

The intersection and set difference (A-B) on text files

Getting ready

How to do it...

How it works...

Finding and deleting duplicate files

Getting ready

How to do it...

How it works...

Working with file permissions, ownership, and the sticky bit

How to do it...

There's more...

Changing ownership

Setting sticky bit

Applying permissions recursively to files

Applying ownership recursively

Running an executable as a different user (setuid)

Making files immutable

Getting ready

How to do it...

Generating blank files in bulk

Getting ready

How to do it...

Finding symbolic links and their targets

How to do it...

How it works...

Enumerating file type statistics

Getting ready

How to do it...

How it works...

Using loopback files

How to do it...

How it works...

There's more...

Creating partitions inside loopback images

Quicker way to mount loopback disk images with partitions

Mounting ISO files as loopback

Flush changing immediately with sync

Creating ISO files and hybrid ISO

Getting ready

How to do it...

There's more...

Hybrid ISO that boots off a flash drive or hard disk

Burning an ISO from the command line

Playing with the CD-ROM tray

Finding the difference between files, patching

How to do it...

There's more...

Generating difference against directories

Using head and tail for printing the last or first 10 lines

How to do it...

Listing only directories – alternative methods

Getting ready

How to do it...

How it works...

Fast command-line navigation using pushd and popd

Getting ready

How to do it...

There's more...

Most frequently used directory switching

Counting the number of lines, words, and characters in a file

How to do it...

Printing the directory tree

Getting ready

How to do it...

There's more...

HTML output for tree

4. Texting and Driving

Introduction

Using regular expressions

How to do it...

How it works...

There's more...

Treatment of special characters

Visualizing regular expressions

Searching and mining a text inside a file with grep

How to do it...

There's more...

Recursively search many files

Ignoring case of pattern

grep by matching multiple patterns

Including and excluding files in a grep search

Using grep with xargs with zero-byte suffix

Silent output for grep

Printing lines before and after text matches

Cutting a file column-wise with cut

How to do it...

There's more

Specifying the range of characters or bytes as fields

Using sed to perform text replacement

How to do it…

There's more...

Removing blank lines

Performing replacement directly in the file

Matched string notation (&)

Substring match notation (\1)

Combination of multiple expressions

Quoting

Using awk for advanced text processing

Getting ready...

How to do it…

How it works…

There's more…

Special variables

Passing an external variable to awk

Reading a line explicitly using getline

Filtering lines processed by awk with filter patterns

Setting delimiter for fields

Reading the command output from awk

Using loop inside awk

String manipulation functions in awk

Finding the frequency of words used in a given file

Getting ready

How to do it...

How it works...

See also

Compressing or decompressing JavaScript

Getting ready

How to do it...

How it works...

See also

Merging multiple files as columns

How to do it...

See also

Printing the nth word or column in a file or line

How to do it...

See also

Printing text between line numbers or patterns

Getting ready

How to do it...

See also

Printing lines in the reverse order

Getting ready

How to do it...

How it works...

Parsing e-mail addresses and URLs from text

How to do it...

How it works...

See also

Removing a sentence in a file containing a word

Getting ready

How to do it...

How it works...

See also

Replacing a pattern with text in all the files in a directory

How to do it...

How it works...

There's more...

Text slicing and parameter operations

How to do it...

See also

5. Tangled Web? Not At All!

Introduction

Downloading from a web page

Getting ready

How to do it...

How it works...

There's more...

Restricting the download speed

Resume downloading and continue

Copying a complete website (mirroring)

Accessing pages with HTTP or FTP authentication

Downloading a web page as plain text

How to do it...

A primer on cURL

Getting ready

How to do it…

How it works...

There's more...

Continuing and resuming downloads

Setting the referer string with cURL

Cookies with cURL

Setting a user agent string with cURL

Specifying a bandwidth limit on cURL

Specifying the maximum download size

Authenticating with cURL

Printing response headers excluding the data

See also

Accessing Gmail e-mails from the command line

How to do it...

How it works...

See also

Parsing data from a website

How to do it...

How it works...

See also

Image crawler and downloader

How to do it...

How it works...

See also

Web photo album generator

Getting ready

How to do it...

How it works...

See also

Twitter command-line client

Getting ready

How to do it...

How it works...

See also

Creating a "define" utility by using the Web backend

Getting ready

How to do it...

How it works...

See also

Finding broken links in a website

Getting ready

How to do it...

How it works...

See also

Tracking changes to a website

Getting ready

How to do it...

How it works...

See also

Posting to a web page and reading the response

Getting ready

How to do it...

How it works...

See also

6. The Backup Plan

Introduction

Archiving with tar

Getting ready

How to do it...

How it works...

There's more...

Appending files to an archive

Extracting files and folders from an archive

stdin and stdout with tar

Concatenating two archives

Updating files in an archive with a timestamp check

Comparing files in the archive and file system

Deleting files from the archive

Compression with the tar archive

Excluding a set of files from archiving

Excluding version control directories

Printing total bytes

See also

Archiving with cpio

How to do it...

How it works...

Compressing data with gzip

How to do it...

There's more...

Gzip with tarball

zcat - reading gzipped files without extracting

Compression ratio

Using bzip2

Using lzma

See also

Archiving and compressing with zip

How to do it...

How it works...

Faster archiving with pbzip2

Getting ready

How to do it...

How it works...

There's more...

Manually specifying the number of CPUs

Specifying the compression ratio

Creating filesystems with compression

Getting ready

How to do it...

There's more...

Excluding files while creating a squashfs file

Backup snapshots with rsync

How to do it...

How it works...

There's more...

Excluding files while archiving with rsync

Deleting non-existent files while updating rsync backup

Scheduling backups at intervals

Version control-based backup with Git

Getting ready

How to do it...

Creating entire disk images using fsarchiver

Getting ready

How to do it...

How it works...

7. The Old-boy Network

Introduction

Setting up the network

Getting ready

How to do it...

There's more...

Printing the list of network interfaces

Displaying IP addresses

Spoofing the hardware address (MAC address)

Name server and DNS (Domain Name Service)

DNS lookup

Showing routing table information

See also

Let us ping!

How to do it...

There's more

Round trip time

Limiting the number of packets to be sent

Return status of the ping command

Traceroute

Listing all the machines alive on a network

Getting ready

How to do it...

How it works...

There's more...

Parallel pings

Using fping

See also

Running commands on a remote host with SSH

Getting ready

How to do it...

There's more...

SSH with compression

Redirecting data into stdin of remote host shell commands

Running graphical commands on a remote machine

See also

Transferring files through the network

Getting ready

How to do it...

There's more...

Automated FTP transfer

SFTP (Secure FTP)

The rsync command

SCP (secure copy program)

Recursive copying with SCP

See also

Connecting to a wireless network

Getting ready

How to do it...

How it works...

See also

Password-less auto-login with SSH

Getting ready

How to do it...

Port forwarding using SSH

How to do it...

There's more...

Non-interactive port forward

Reverse port forwarding

Mounting a remote drive at a local mount point

Getting ready

How to do it...

See also

Network traffic and port analysis

Getting ready

How to do it...

How it works...

There's more...

Opened port and services using netstat

Creating arbitrary sockets

Getting ready

How to do it...

There's more...

Quickly copying files over the network

Sharing an Internet connection

Getting ready

How to do it...

Basic firewall using iptables

How to do it...

How it works...

There's more...

8. Put on the Monitor's Cap

Introduction

Monitoring disk usage

Getting ready

How to do it...

There's more...

Displaying disk usage in KB, MB, or Blocks

Displaying the grand total sum of disk usage

Printing files in specified units

Excluding files from the disk usage calculation

Finding the 10 largest size files from a given directory

Disk free information

Calculating the execution time for a command

How to do it...

How it works...

Collecting information about logged in users, boot logs, and boot failures

Getting ready

How to do it...

Listing the top 10 CPU consuming processes in an hour

Getting ready

How to do it...

How it works...

See also

Monitoring command outputs with watch

How to do it...

There's more

Highlighting the differences in the watch output

Logging access to files and directories

Getting ready

How to do it...

How it works...

Logfile management with logrotate

Getting ready

How to do it...

How it works...

Logging with syslog

Getting ready

How to do it...

See also

Monitoring user logins to find intruders

Getting ready

How to do it…

How it works…

Remote disk usage health monitor

Getting ready

How to do it…

How it works…

See also

Finding out active user hours on a system

Getting ready

How to do it…

How it works…

Measuring and optimizing power usage

Getting ready

How to do it...

Monitoring disk activity

Getting ready

How to do it...

Checking disks and filesystems for errors

Getting ready

How to do it...

How it works...

9. Administration Calls

Introduction

Gathering information about processes

Getting ready

How to do it...

How it works...

There's more...

top

Sorting the ps output with respect to a parameter

Finding the process ID when given command names

Filters with ps for real user or ID, effective user or ID

TTY filter for ps

Information about process threads

Specifying output width and columns to be displayed

Showing environment variables for a process

About which, whereis, file, whatis, and load average

See also

Killing processes and send or respond to signals

Getting ready

How to do it...

There's more...

The kill family of commands

Capturing and responding to signals

Sending messages to user terminals

Getting ready

How to do it...

How it works...

Gathering system information

How to do it...

Using /proc for gathering information

How to do it...

Scheduling with cron

Getting ready

How to do it…

How it works...

There's more…

Specifying environment variables

Running commands at system start up/boot

Viewing the cron table

Removing the cron table

Writing and reading the MySQL database from Bash

Getting ready

How to do it…

How it works…

User administration script

How to do it…

How it works…

Bulk image resizing and format conversion

Getting ready

How to do it..

How it works…

See also

Taking screenshots from the terminal

Getting ready

How to do it...

Managing multiple terminals from one

Getting ready

How to do it...

Index