Linux Shell Scripting Essentials

Book Image

Linux Shell Scripting Essentials

Book Image

Linux Shell Scripting Essentials

Overview of this book

Linux Shell Scripting Essentials

Linux Shell Scripting Essentials

Credits

About the Author

About the Author

About the Reviewers

About the Reviewers

www.PacktPub.com

www.PacktPub.com

Preface

Free Chapter

The Beginning of the Scripting Journey

The Beginning of the Scripting Journey

Hello World in shell

Define variables of choice

Builtin shell variables

Shell expansions

Construct commands using eval

Make bash behave using set

Getting Hands-on with I/O, Redirection Pipes, and Filters

Getting Hands-on with I/O, Redirection Pipes, and Filters

Standard I/O and error streams

Redirecting the standard I/O and error streams

Pipe and pipelines – connecting commands

Regular expressions

Filtering an output using grep

Editing output using sed

Duplicating a stream using tee

Sorting and finding unique text

Character-based translation using tr

Filtering based on lines—head and tail

The Cut-based selection

Effective Script Writing

Effective Script Writing

Exiting from scripts and exit codes

Testing expressions with a test

Using conditional statements with if and else

Indexed arrays and associative arrays

Looping around with for

The select, while, and until loops

Switch to my choice

Passing stdout as a parameter using xargs

Using functions and positional parameters

Modularizing and Debugging

Modularizing and Debugging

Modularizing your scripts

Passing command line parameters to script

Debugging your scripts

Command completion

Customizing the Environment

Customizing the Environment

Knowing the default environment

Modifying a shell environment

Using bash startup files

Knowing your history

Task management

Working with Files

Working with Files

Performing basic file operations

Moving and copying files

Comparing files

Links to a file

Temporary files

Permission and ownership

Getting the list of open files

Configuration files

Welcome to the Processes

Welcome to the Processes

Process management

Listing and monitoring processes

Process substitution

Process scheduling priorities

Inter-process communication

Scheduling Tasks and Embedding Languages in Scripts

Scheduling Tasks and Embedding Languages in Scripts

Running tasks at a specific time

Managing the crontab entry

Embedding languages

Index

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Character-based translation using tr

Another interesting shell command is tr. This translates, squeezes, or deletes characters from the standard input. The syntax will be as follows:

tr [OPTION]... SET1 [SET2]

The options for the tr commands are explained in the following table:

Option	Description
`-c, -C`	Use complement of SET1
`-d`	This deletes a range of characters specified in SET1.
`-s`	This replaces consecutive multiple occurrences of characters in SET1 with a single occurrence.
`-t`	This truncates SET1 to the length of SET2. Any extra characters in SET1 will be not considered for translation.

SETs are a string of characters that can be specified using the following:

A character class: [:alnum:], [:digit:], [:alpha:] and so on
A character range: 'a-z', 'A-Z', and '0-9'
An escape character: \\, \b, \r, \n, \f, \v, and \t

To provide an input text from a file and an output to a file, we can use the file redirection operators: < (less than for input) and > (greater than for...