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Command Line Fundamentals
Command Line Fundamentals

Command Line Fundamentals: Learn to use the Unix command-line tools and Bash shell scripting

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Profile Icon Vivek Nagarajan
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€29.99
Paperback Dec 2018 314 pages 1st Edition
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€15.99 €23.99
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Arrow left icon
Profile Icon Vivek Nagarajan
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€29.99
Paperback Dec 2018 314 pages 1st Edition
eBook
€15.99 €23.99
Paperback
€29.99
Subscription
Free Trial
Renews at €18.99p/m
eBook
€15.99 €23.99
Paperback
€29.99
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Renews at €18.99p/m

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Command Line Fundamentals

Command-Line Building Blocks

Learning Objectives

By the end of the chapter, you will be able to:

  • Use redirection to control command input and output
  • Construct pipelines between commands
  • Use commands for text filtering
  • Use text transformation commands
  • Analyze tabular data using data-processing commands

This chapter introduces you to the two main composing mechanisms of command lines: redirection and piping. You will also expand your vocabulary of commands to be able to perform a wide variety of data-processing tasks.

Introduction

So far, we have learned the basics of how to work with the filesystem with the shell. We also looked at some shell mechanisms such as wildcards and completion that simplify life in the command line. In this chapter, we will examine the building blocks that are used to perform data-processing tasks on the shell.

The Unix approach is to favor small, single-purpose utilities with very well-defined interfaces. Redirection and pipes let us connect these small commands and files together so that we can compose them like the elements of an electronic circuit to perform complex tasks. This concept of joining together small units into a more complex mechanism is a very powerful technique.

Most data that we typically work with is textual in nature, so we will study the most useful text-oriented commands in this chapter, along with various practical examples of their usage.

Redirection

Redirection is a method of connecting files to a command. This mechanism is used to capture the output of a command or to feed input to it.

Note

During this section, we will introduce a few commands briefly, in order to illustrate some concepts. The commands are only used as examples, and their usage does not have any connection to the main topics being covered here. The detailed descriptions of all the features and uses of those commands will be covered in the topic on text-processing commands.

Input and Output Streams

Every command that is run has a channel for data input, termed standard input (stdin), data output, termed standard output (stdout) and standard error (stderr). A command reads data from stdin and writes its results to stdout. If any error occurs, the error messages are written to stderr. These channels can also be thought of as streams through which data flows.

By convention, stdin, stdout, and stderr are assigned the numbers 0, 1, and 2...

Pipes

A shell pipeline or simply a pipeline refers to a construct where data is pushed from one command to another in an assembly line fashion. It is expressed as a series of commands separated by a pipe symbol |. These pipes connect the stdout of each command to the stdin of the subsequent command. Internally, a pipe is a special memory FIFO (first in, first out) buffer provided by the OS.

The basic syntax of a pipeline is as follows:

command1 | command2

Any number of commands can be linked:

command1 | command2 | command3 | command4

Pipelines are analogous to assembly lines in a factory. Like an assembly line lets multiple workers simultaneously do one designated job repeatedly, ending up with a finished product, a pipeline lets a series of commands work on a stream of data, each doing one task, eventually leading to the desired output.

Pipelines ensure maximum throughput and optimal usage of computing power. The time taken for a pipeline task in most cases will...

Text-Processing Commands

In the previous sections, we learned about the two main composing mechanisms of command lines: redirection and piping. In this topic, we will expand our vocabulary of commands that, when combined, let us do a wide variety of data-processing tasks.

We focus on text-processing because it applies to a wide range of real-life data, and will be useful to professionals in any field. A huge amount of data on the internet is in textual form, and text happens to be the easiest way to share data in a portable way as simple columnar CSV (comma-separated values) or TSV (tab-separated values) files. Once you learn these commands, you do not have to rely on the knowledge of any specific software GUI tool, and you can run complex tasks on the shell itself. In many cases, running a quick shell pipeline is much faster than setting up the data in a more complex GUI tool. In a later chapter, you will learn how to save your commands as a sort of automatic recipe, with shell...

Summary

In this chapter, you have been introduced to several concepts such as input, output, redirection, and pipelines. You have also learned basic text-processing tools, along with both common and uncommon use cases of these tools, to demonstrate their flexibility. At a conceptual level, several techniques related to processing tabular data have been explored.

A large number of details have been covered. If you are being introduced to these for the first time, you should attempt to understand the concepts at an abstract level and not be overwhelmed by details (which you can always refer to when in doubt). To this end, some additional complexities have been avoided in order to focus on the essential concepts. The students can pick up more nuances as they continue to learn and practice in the future, beyond this brief book.

In the next chapter, you will learn about several more concepts related to the shell, including basic regular expressions, shell expansion, and command substitution...

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Key benefits

  • Learn why the Bash shell is widely used on Linux and iOS
  • Explore advanced shell concepts, such as pipes and redirection
  • Understand how to use Unix command-line tools as building blocks for different tasks

Description

The most basic interface to a computer—the command line—remains the most flexible and powerful way of processing data and performing and automating various day-to-day tasks. Command Line Fundamentals begins by exploring the basics, and then focuses on the most common tool, the Bash shell (which is standard on all Linux and iOS systems). As you make your way through the book, you'll explore the traditional Unix command-line programs as implemented by the GNU project. You'll also learn to use redirection and pipelines to assemble these programs to solve complex problems. By the end of this book, you'll have explored the basics of shell scripting, allowing you to easily and quickly automate tasks.

Who is this book for?

Command Line Fundamentals is for programmers who use GUIs but want to understand how to use the command line to complete tasks faster.

What you will learn

  • Use the Bash shell to run commands
  • Utilize basic Unix utilities such as cat, tr, sort, and uniq
  • Explore shell wildcards to manage groups of files
  • Apply useful keyboard shortcuts in shell
  • Employ redirection and pipes to process data
  • Write both basic and advanced shell scripts to automate tasks
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Product Details

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Publication date, Length, Edition, Language, ISBN-13
Publication date : Dec 24, 2018
Length: 314 pages
Edition : 1st
Language : English
ISBN-13 : 9781789807769
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Product Details

Publication date : Dec 24, 2018
Length: 314 pages
Edition : 1st
Language : English
ISBN-13 : 9781789807769
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Table of Contents

4 Chapters
Introduction to the Command Line Chevron down icon Chevron up icon
Command-Line Building Blocks Chevron down icon Chevron up icon
Advanced Command-Line Concepts Chevron down icon Chevron up icon
Shell Scripting Chevron down icon Chevron up icon
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