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“Shaw_FM” — 2014/11/8 — 17:24 — page 1 — #1 LEARN RUBY THE HARD WAY Third Edition “Shaw_FM” — 2014/11/8 — 17:24 — page 2 — #2 “Shaw_FM” — 2014/11/8 — 17:24 — page 3 — #3 LEARN RUBY THE HARD WAY A Simple and Idiomatic Introduction to the Imaginative World of Computational Thinking with Code Third Edition Zed A. Shaw Upper Saddle River, NJ • Boston • Indianapolis • San Francisco New York • Toronto • Montreal • London • Munich • Paris • Madrid Capetown • Sydney • Tokyo • Singapore • Mexico City “Shaw_FM” — 2014/11/8 — 17:24 — page 4 — #4 Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and the publisher was aware of a trademark claim, the designations have been printed with initial capital letters or in all capitals. The author and publisher have taken care in the preparation of this book, but make no expressed or implied warranty of any kind and assume no responsibility for errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of the use of the information or programs contained herein. For information about buying this title in bulk quantities, or for special sales opportunities (which may include electronic versions; custom cover designs; and content particular to your business, training goals, marketing focus, or branding interests), please contact our corporate sales department at [email protected] or (800) 382-3419. For government sales inquiries, please contact [email protected]. For questions about sales outside the United States, please contact [email protected]. Visit us on the Web: informit.com/hardway Library of Congress Cataloging-in-Publication Data Shaw, Zed, author. Learn Ruby the hard way : a simple and idiomatic introduction to the imaginative world of computational thinking with code / Zed A. Shaw.—Third edition. pages cm Includes index. ISBN 978-0-321-88499-2 (pbk. : alk. paper) 1. Ruby (Computer program language) I. Title. QA76.73.R83S536 2014 005.1’17—dc23 2014033534 Copyright © 2015 Zed A. Shaw All rights reserved. Printed in the United States of America. This publication is protected by copyright, and permission must be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. To obtain permission to use material from this work, please submit a written request to Pearson Education, Inc., Permissions Department, One Lake Street, Upper Saddle River, New Jersey 07458, or you may fax your request to (201) 236-3290. ISBN-13: 978-0-321-88499-2 ISBN-10: 0-321-88499-X Text printed in the United States on recycled paper at RR Donnelley in Crawfordsville, Indiana. First printing, December 2014 “Shaw_FM” — 2014/11/8 — 17:24 — page v — #5 v Contents Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 The Hard Way Is Easier . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Reading and Writing . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Attention to Detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Spotting Differences . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Do Not Copy-Paste . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Using the Included Videos . . . . . . . . . . . . . . . . . . . . . . . . 3 A Note on Practice and Persistence . . . . . . . . . . . . . . . . . . . 3 A Warning for the Smarties . . . . . . . . . . . . . . . . . . . . . . . 4 Exercise 0 The Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Mac OS X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 OS X: What You Should See . . . . . . . . . . . . . . . . . . . . . 7 Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Windows: What You Should See . . . . . . . . . . . . . . . . . . . 8 Linux . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Linux: What You Should See . . . . . . . . . . . . . . . . . . . . . 9 Finding Things on the Internet . . . . . . . . . . . . . . . . . . . . . 10 Warnings for Beginners . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Exercise 1 A Good First Program . . . . . . . . . . . . . . . . . . . . . . 12 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 17 Exercise 2 Comments and Pound Characters . . . . . . . . . . . . . . . 18 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 19 Exercise 3 Numbers and Math . . . . . . . . . . . . . . . . . . . . . . . 20 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 22 “Shaw_FM” — 2014/11/8 — 17:24 — page vi — #6 vi CONTENTS Exercise 4 Variables and Names . . . . . . . . . . . . . . . . . . . . . . 24 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 25 Exercise 5 More Variables and Printing . . . . . . . . . . . . . . . . . . 28 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 29 Exercise 6 Strings and Text . . . . . . . . . . . . . . . . . . . . . . . . . 30 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Common Student Question . . . . . . . . . . . . . . . . . . . . . . . 31 Exercise 7 More Printing . . . . . . . . . . . . . . . . . . . . . . . . . . 32 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 33 Exercise 8 Printing, Printing . . . . . . . . . . . . . . . . . . . . . . . . 34 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 35 Exercise 9 Printing, Printing, Printing . . . . . . . . . . . . . . . . . . . 36 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 37 Exercise 10 What Was That? . . . . . . . . . . . . . . . . . . . . . . . . 38 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Escape Sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 40 Exercise 11 Asking Questions . . . . . . . . . . . . . . . . . . . . . . . . 42 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Common Student Question . . . . . . . . . . . . . . . . . . . . . . . 43 Exercise 12 Prompting People for Numbers . . . . . . . . . . . . . . . 44 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 “Shaw_FM” — 2014/11/8 — 17:24 — page vii — #7 CONTENTS Exercise 13 Parameters, Unpacking, Variables . . . . . . . . . . . . . . 46 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 47 Exercise 14 Prompting and Passing . . . . . . . . . . . . . . . . . . . . 50 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 51 Exercise 15 Reading Files . . . . . . . . . . . . . . . . . . . . . . . . . . 52 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 54 Exercise 16 Reading and Writing Files . . . . . . . . . . . . . . . . . . . 56 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 58 Exercise 17 More Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 61 Exercise 18 Names, Variables, Code, Functions . . . . . . . . . . . . . . 62 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 65 Exercise 19 Functions and Variables . . . . . . . . . . . . . . . . . . . . 66 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 67 Exercise 20 Functions and Files . . . . . . . . . . . . . . . . . . . . . . . 70 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 71 Exercise 21 Functions Can Return Something . . . . . . . . . . . . . . 74 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 76 vii “Shaw_FM” — 2014/11/8 — 17:24 — page viii — #8 viii CONTENTS Exercise 22 What Do You Know So Far? . . . . . . . . . . . . . . . . . 78 What You Are Learning . . . . . . . . . . . . . . . . . . . . . . . . . . 78 Exercise 23 Read Some Code . . . . . . . . . . . . . . . . . . . . . . . . 80 Exercise 24 More Practice . . . . . . . . . . . . . . . . . . . . . . . . . . 82 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 83 Exercise 25 Even More Practice . . . . . . . . . . . . . . . . . . . . . . . 84 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 87 Exercise 26 Congratulations, Take a Test! . . . . . . . . . . . . . . . . . 88 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 88 Exercise 27 Memorizing Logic . . . . . . . . . . . . . . . . . . . . . . . 90 The Truth Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 The Truth Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 Common Student Question . . . . . . . . . . . . . . . . . . . . . . . 92 Exercise 28 Boolean Practice . . . . . . . . . . . . . . . . . . . . . . . . 94 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 96 Exercise 29 What If . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 Common Student Question . . . . . . . . . . . . . . . . . . . . . . . 99 Exercise 30 Else and If . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Common Student Question . . . . . . . . . . . . . . . . . . . . . . . 101 Exercise 31 Making Decisions . . . . . . . . . . . . . . . . . . . . . . . . 102 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 103 Exercise 32 Loops and Arrays . . . . . . . . . . . . . . . . . . . . . . . . 106 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 “Shaw_FM” — 2014/11/8 — 17:24 — page ix — #9 CONTENTS Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 108 Exercise 33 While Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 112 Exercise 34 Accessing Elements of Arrays . . . . . . . . . . . . . . . . . 114 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 Exercise 35 Branches and Functions . . . . . . . . . . . . . . . . . . . . 116 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 118 Exercise 36 Designing and Debugging . . . . . . . . . . . . . . . . . . 120 Rules for If-Statements . . . . . . . . . . . . . . . . . . . . . . . . . . 120 Rules for Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 Tips for Debugging . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Homework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Exercise 37 Symbol Review . . . . . . . . . . . . . . . . . . . . . . . . . 122 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 String Escape Sequences . . . . . . . . . . . . . . . . . . . . . . . . . 124 Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 Reading Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 Common Student Question . . . . . . . . . . . . . . . . . . . . . . . 127 Exercise 38 Doing Things to Arrays . . . . . . . . . . . . . . . . . . . . 128 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 What Arrays Can Do . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 When to Use Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 131 Exercise 39 Hashes, Oh Lovely Hashes . . . . . . . . . . . . . . . . . . . 132 A Hash Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 What Hashes Can Do . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 ix “Shaw_FM” — 2014/11/8 — 17:24 — page x — #10 x CONTENTS Making Your Own Hash Module . . . . . . . . . . . . . . . . . . . . 136 The Code Description . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 Three Levels of Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 What You Should See (Again) . . . . . . . . . . . . . . . . . . . . . . 142 When to Use Hashes or Arrays . . . . . . . . . . . . . . . . . . . . . . 143 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 144 Exercise 40 Modules, Classes, and Objects . . . . . . . . . . . . . . . . 146 Modules Are Like Hashes . . . . . . . . . . . . . . . . . . . . . . . . . 146 Classes Are Like Modules . . . . . . . . . . . . . . . . . . . . . . . 148 Objects Are Like Require . . . . . . . . . . . . . . . . . . . . . . . 148 Getting Things from Things A First Class Example . . . . . . . . . . . . . . . . . . . . . 150 . . . . . . . . . . . . . . . . . . . . . . . . . 150 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 Common Student Question . . . . . . . . . . . . . . . . . . . . . . . 151 Exercise 41 Learning to Speak Object Oriented . . . . . . . . . . . . . 152 Word Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 Phrase Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 Combined Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 A Reading Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 Practice English to Code . . . . . . . . . . . . . . . . . . . . . . . . . 156 Reading More Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 156 Exercise 42 Is-A, Has-A, Objects, and Classes . . . . . . . . . . . . . . . 158 How This Looks in Code . . . . . . . . . . . . . . . . . . . . . . . . . 159 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 161 Exercise 43 Basic Object-Oriented Analysis and Design . . . . . . . . . 164 The Analysis of a Simple Game Engine . . . . . . . . . . . . . . . . . 165 Write or Draw about the Problem . . . . . . . . . . . . . . . . . . 165 Extract Key Concepts and Research Them . . . . . . . . . . . . . 166 Create a Class Hierarchy and Object Map for the Concepts . . . 167 Code the Classes and a Test to Run Them . . . . . . . . . . . . . . 168 “Shaw_FM” — 2014/11/8 — 17:24 — page xi — #11 CONTENTS Repeat and Re ne . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 Top Down Versus Bottom Up . . . . . . . . . . . . . . . . . . . . . . 170 The Code for ”Gothons from Planet Percal #25” . . . . . . . . . . . 170 What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 Common Student Question . . . . . . . . . . . . . . . . . . . . . . . 177 Exercise 44 Inheritance Versus Composition . . . . . . . . . . . . . . . 178 What Is Inheritance? . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 Implicit Inheritance . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Override Explicitly . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 Alter Before or After . . . . . . . . . . . . . . . . . . . . . . . . . 180 All Three Combined . . . . . . . . . . . . . . . . . . . . . . . . . . 182 Using super() with initialize . . . . . . . . . . . . . . . . . . 183 Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 When to Use Inheritance or Composition . . . . . . . . . . . . . . . 185 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 186 Exercise 45 You Make a Game . . . . . . . . . . . . . . . . . . . . . . . 188 Evaluating Your Game . . . . . . . . . . . . . . . . . . . . . . . . . . 188 Function Style . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 Class Style . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 Code Style . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 Good Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 Evaluate Your Game . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 Exercise 46 A Project Skeleton . . . . . . . . . . . . . . . . . . . . . . . 192 Creating the Skeleton Project Directory . . . . . . . . . . . . . . . . 192 Final Directory Structure . . . . . . . . . . . . . . . . . . . . . . . 193 Testing Your Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 Using the Skeleton . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 Required Quiz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 196 Exercise 47 Automated Testing . . . . . . . . . . . . . . . . . . . . . . 198 Writing a Test Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 Testing Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 xi “Shaw_FM” — 2014/11/8 — 17:24 — page xii — #12 xii CONTENTS What You Should See . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 202 Exercise 48 Advanced User Input . . . . . . . . . . . . . . . . . . . . . 204 Our Game Lexicon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 Breaking Up a Sentence . . . . . . . . . . . . . . . . . . . . . . . . 205 Lexicon Tuples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 Scanning Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 Exceptions and Numbers . . . . . . . . . . . . . . . . . . . . . . . 206 A Test First Challenge . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 What You Should Test . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 210 Exercise 49 Making Sentences . . . . . . . . . . . . . . . . . . . . . . . 212 Match and Peek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212 The Sentence Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . 213 A Word on Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . 213 The Parser Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 Playing with the Parser . . . . . . . . . . . . . . . . . . . . . . . . . . 216 What You Should Test . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 Common Student Question . . . . . . . . . . . . . . . . . . . . . . . 217 Exercise 50 Your First Website . . . . . . . . . . . . . . . . . . . . . . . 218 Installing Sinatra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 Make a Simple ”Hello World” Project . . . . . . . . . . . . . . . . . 219 What’s Happening Here? . . . . . . . . . . . . . . . . . . . . . . . . . 220 Stopping and Reloading Sinatra . . . . . . . . . . . . . . . . . . . . . 221 Fixing Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 Create Basic Templates . . . . . . . . . . . . . . . . . . . . . . . . . . 222 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 Common Student Questions . . . . . . . . . . . . . . . . . . . . . . . 223 Exercise 51 Getting Input from a Browser . . . . . . . . . . . . . . . . 224 How the Web Works . . . . . . . . . . . . . . . . . . . . . . . . . . . 224 How Forms Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 “Shaw_FM” — 2014/11/8 — 17:24 — page xiii — #13 CONTENTS Creating HTML Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 Creating a Layout Template . . . . . . . . . . . . . . . . . . . . . . . 228 Writing Automated Tests for Forms . . . . . . . . . . . . . . . . . . . 229 Study Drills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230 Common Student Question . . . . . . . . . . . . . . . . . . . . . . . 231 Exercise 52 The Start of Your Web Game . . . . . . . . . . . . . . . . . 232 Refactoring the Exercise 43 Game . . . . . . . . . . . . . . . . . . . . 232 Sessions and Tracking Users . . . . . . . . . . . . . . . . . . . . . . . 237 Creating an Engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 Your Final Exam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 Next Steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242 How to Learn Any Programming Language . . . . . . . . . . . . . . 243 Advice from an Old Programmer . . . . . . . . . . . . . . . . . . . . . . 246 Appendix Command Line Crash Course . . . . . . . . . . . . . . . . . . 249 Introduction: Shut Up and Shell . . . . . . . . . . . . . . . . . . . . . 249 How to Use This Appendix . . . . . . . . . . . . . . . . . . . . . . 249 You Will Be Memorizing Things . . . . . . . . . . . . . . . . . . . 250 The Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 Do This . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 You Learned This . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252 Do More . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252 Paths, Folders, and Directories (pwd) . . . . . . . . . . . . . . . . . . 254 Do This . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255 You Learned This . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 Do More . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 If You Get Lost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 Do This . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 You Learned This . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 Make a Directory (mkdir) . . . . . . . . . . . . . . . . . . . . . . . . . 257 Do This . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 You Learned This . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 Do More . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 Change Directory (cd) . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 Do This . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 xiii “Shaw_FM” — 2014/11/8 — 17:24 — page xiv — #14 xiv CONTENTS You Learned This . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263 Do More . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264 List Directory (ls) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264 Do This . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264 You Learned This . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 Do More . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 Remove Directory (rmdir) . . . . . . . . . . . . . . . . . . . . . . . . . 269 Do This . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270 You Learned This . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 Do More . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 Moving Around (pushd, popd) . . . . . . . . . . . . . . . . . . . . . 273 Do This . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 You Learned This . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 Do More . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 Making Empty Files (Touch, New-Item) . . . . . . . . . . . . . . . . . 276 Do This . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276 You Learned This . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 Do More . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 Copy a File (cp) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 Do This . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 You Learned This . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 Do More . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 Moving a File (mv) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 Do This . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 You Learned This . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 Do More . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 View a File (less, MORE) Do This . . . . . . . . . . . . . . . . . . . . . . . . . 283 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 You Learned This . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 Do More . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 Stream a File (cat) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 Do This . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 You Learned This . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286 Do More . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286 “Shaw_FM” — 2014/11/8 — 17:24 — page xv — #15 CONTENTS Removing a File (rm) . . . . . . . . . . . . . . . . . . . . . . . . . . . 286 Do This . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286 You Learned This . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 Do More . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 Exiting Your Terminal (exit) . . . . . . . . . . . . . . . . . . . . . . . 289 Do This . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 You Learned This . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 Do More . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 Command Line Next Steps . . . . . . . . . . . . . . . . . . . . . . . . 290 UNIX Bash References . . . . . . . . . . . . . . . . . . . . . . . . . 290 PowerShell References . . . . . . . . . . . . . . . . . . . . . . . . 290 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 xv This page intentionally left blank “Shaw_Preface” — 2014/11/8 — 17:27 — page 1 — #1 1 Preface T his simple book is meant to get you started in programming. The title says it’s the hard way to learn to write code, but it’s actually not. It’s only the ”hard” way because it uses a technique called instruction. Instruction is where I tell you to do a sequence of controlled exercises designed to build a skill through repetition. This technique works very well with beginners, who know nothing and need to acquire basic skills before they can understand more complex topics. It’s used in everything from martial arts to music, to even basic math and reading skills. This book instructs you in Ruby by slowly building and establishing skills through techniques like practice and memorization, then applying them to increasingly dif cult problems. By the end of the book you will have the tools needed to begin learning more complex programming topics. I like to tell people that my book gives you your ”programming black belt.” What this means is that you know the basics well enough to now start learning programming. If you work hard, take your time, and build these skills, you will learn to code. Acknowledgments I would like to thank Angela for helping me with the rst two versions of this book. Without her, I probably wouldn’t have bothered to nish it at all. She did the copyediting of the rst draft, and supported me immensely while I wrote it. I also want to thank Rob Sobers for suggesting I make a Ruby version of my Python book and doing the initial work helping me convert it to use Ruby. I’d also like to thank Greg Newman for doing the original cover art, Brian Shumate for early website designs, and all of the people who read this book and took the time to send me feedback and corrections. Thank you. “Shaw_Ex00” — 2014/11/7 — 18:41 — page 2 — #1 2 The Hard Way Is Easier W ith the help of this book, you will do the incredibly simple things that all programmers do to learn a programming language: 1. Go through each exercise. 2. Type in each sample exactly. 3. Make it run. That’s it. This will be very dif cult at rst, but stick with it. If you go through this book, and do each exercise for one or two hours a night, you will have a good foundation for moving onto another book about Ruby to continue your studies. This book won’t turn you into a programmer overnight, but it will get you started on the path to learning how to code. This book’s job is to teach you the three most essential skills that a beginning programmer needs to know: reading and writing, attention to detail, and spotting differences. Reading and Writing If you have a problem typing, you will have a problem learning to code, and especially if you have a problem typing the fairly odd characters in source code. Without this simple skill you will be unable to learn even the most basic things about how software works. Typing the code samples and getting them to run will help you learn the names of the symbols, get familiar with typing them, and get you reading the language. Attention to Detail The one skill that separates bad programmers from good programmers is attention to detail. In fact, it’s what separates the good from the bad in any profession. You must pay attention to the tiniest details of your work or you will miss important elements of what you create. In programming, this is how you end up with bugs and dif cult-to-use systems. By going through this book, and copying each example exactly, you will be training your brain to focus on the details of what you are doing, as you are doing it. “Shaw_Ex00” — 2014/11/7 — 18:41 — page 3 — #2 THE HARD WAY IS EASIER 3 Spotting Differences A very important skill (that most programmers develop over time) is the ability to visually notice differences between things. An experienced programmer can take two pieces of code that are slightly different and immediately start pointing out the differences. Programmers have invented tools to make this even easier, but we won’t be using any of these. You rst have to train your brain the hard way; then use the tools. While you do these exercises, typing each one in, you will be making mistakes. It’s inevitable; even seasoned programmers would make a few. Your job is to compare what you have written to what’s required, and x all the differences. By doing so, you will train yourself to notice mistakes, bugs, and other problems. Do Not Copy-Paste You must type each of these exercises in, manually. If you copy and paste, you might as well not even do them. The point of these exercises is to train your hands, your brain, and your mind in how to read, write, and see code. If you copy-paste, you are cheating yourself out of the effectiveness of the lessons. Using the Included Videos Learn Ruby the Hard Way has more than ve hours of instructional videos to help you with the book. There is one video for each exercise where I either demonstrate the exercise, or give you tips for completing the exercise. The best way to use the videos is if you are stuck when attempting an exercise or for review after you have completed an exercise. This will slowly wean you off of using videos to learn programming and build your skills at understanding code directly. Stick with it, and slowly you won’t need the videos, or any videos, to learn programming. You’ll be able to just read for the information you need. A Note on Practice and Persistence While you are studying programming, I’m studying how to play guitar. I practice it every day for at least two hours. I play scales, chords, and arpeggios for an hour; and then I learn music theory, ear training, songs, and anything else I can. Some days I study guitar and music for eight hours because I feel like it and it’s fun. To me, repetitive practice is natural and just how to learn something. I know that to get good at anything I have to practice every day, even if I suck that day (which is often) or it’s dif cult. Keep trying and eventually it’ll be easier and fun. “Shaw_Ex00” — 2014/11/7 — 18:41 — page 4 — #3 4 LEARN RUBY THE HARD WAY Between the time that I wrote Learn Python the Hard Way and Learn Ruby the Hard Way, I discovered drawing and painting. I fell in love with making visual art at the age of 39; and I have been spending every day studying it in much the same way that I studied guitar, music, and programming. I collected books of instructional material, did what the books said, painted every day, and focused on enjoying the process of learning. I am by no means an ”artist,” or even that good, but I can now say that I can draw and paint. The same method I’m teaching you in this book applied to my adventures in art. If you break the problem down into small exercises and lessons, and do them every day, you can learn to do almost anything. If you focus on slowly improving and enjoying the learning process, then you will bene t no matter how good you are at it. As you study this book, and continue with programming, remember that anything worth doing is dif cult at rst. Maybe you are the kind of person who is afraid of failure, so you give up at the rst sign of dif culty. Maybe you never learned self-discipline, so you can’t do anything that’s ”boring.” Maybe you were told that you are ”gifted,” so you never attempt anything that might make you seem stupid or not a prodigy. Maybe you are competitive and unfairly compare yourself to someone like me who’s been programming for more than 20 years. Whatever your reason for wanting to quit, keep at it. Force yourself. If you run into a Study Drill you can’t do, or a lesson you just do not understand, then skip it and come back to it later. Just keep going, because with programming there’s this very odd thing that happens. At rst, you will not understand anything. It’ll be weird, just like with learning any human language. You will struggle with words, and not know what symbols are what, and it’ll all be very confusing. Then one day BANG—your brain will snap and you will suddenly ”get it.” If you keep doing the exercises and keep trying to understand them, you will get it. You might not be a master coder, but you will at least understand how programming works. If you give up, you won’t ever reach this point. You will hit the rst confusing thing (which is everything at rst) and then stop. If you keep trying—keep typing it in, trying to understand it and reading about it—you will eventually get it. If you go through this whole book, and you still do not understand how to code, at least you gave it a shot. You can say you tried your best and a little more and it didn’t work out, but at least you tried. You can be proud of that. A Warning for the Smarties Sometimes people who already know a programming language will read this book and feel I’m insulting them. There is nothing in this book that is intended to be interpreted as condescending, insulting, or belittling. I simply know more about programming than my intended readers. If you think you are smarter than me, then you will feel talked down to and there’s nothing I can do about that because you are not my intended reader. “Shaw_Ex00” — 2014/11/7 — 18:41 — page 5 — #4 THE HARD WAY IS EASIER 5 If you are reading this book and ipping out at every third sentence because you feel I’m insulting your intelligence, then I have three points of advice for you: 1. Stop reading my book. I didn’t write it for you. I wrote it for people who don’t already know everything. 2. Empty before you ll. You will have a hard time learning from someone with more knowledge if you already know everything. 3. Go learn Lisp. I hear people who know everything really like Lisp. For everyone else who’s here to learn, just read everything as if I’m smiling and I have a mischievous little twinkle in my eye. “Shaw_Ex01” — 2014/11/7 — 14:08 — page 12 — #1 12 EXERCISE 1 A Good First Program Y ou should have spent a good amount of time in Exercise 0 learning how to install a text editor, run the text editor, run Terminal, and work with both of them. If you haven’t done that, then do not go on. You will not have a good time. This is the only time I’ll start an exercise with a warning that you should not skip or get ahead of yourself. Type the following text into a single le named ex1.rb. Ruby works best with les ending in .rb. 1 2 3 4 5 6 7 puts puts puts puts puts puts puts "Hello World!" "Hello Again" "I like typing this." "This is fun." "Yay! Printing." "I'd much rather you 'not'." 'I "said" do not touch this.' ex1.rb If you are on Mac OS X, then this is what your text editor might look like if you use TextWrangler: “Shaw_Ex01” — 2014/11/7 — 14:08 — page 13 — #2 A GOOD FIRST PROGRAM 13 If you are on Windows using Notepad++, then this is what it would look like: Don’t worry if your editor doesn’t look exactly the same, it should be close though. When you create this le, keep in mind these points: 1. I did not type the line numbers on the left. Those are printed in the book so I can talk about speci c lines by saying, ”See line 5.” You do not type line numbers into Ruby scripts. 2. I have the puts at the beginning of the line and it looks exactly the same as what I have in ex1.rb. Exactly means exactly, not kind of sort of the same. Every single character has to match for it to work. Color doesn’t matter, only the characters you type. In Terminal run the le by typing: ruby ex1.rb If you did it right, then you should see the same output as in the What You Should See section of this exercise. If not, you have done something wrong. No, the computer is not wrong. “Shaw_Ex01” — 2014/11/7 — 14:08 — page 14 — #3 14 LEARN RUBY THE HARD WAY What You Should See On Mac OS X in Terminal you should see this: “Shaw_Ex01” — 2014/11/7 — 14:08 — page 15 — #4 A GOOD FIRST PROGRAM 15 On Windows in PowerShell you should see this: You may see different names before the ruby ex1.rb command, but the important part is that you type the command and see the output is the same as mine. “Shaw_Ex01” — 2014/11/7 — 14:08 — page 16 — #5 16 LEARN RUBY THE HARD WAY If you have an error, it will look like this: > ruby ex1.rb ex1.rb:3: syntax error, unexpected tCONSTANT, expecting $end puts "I like typing this." It’s important that you can read these error messages, because you will be making many of these mistakes. Even I make many of these mistakes. Let’s look at this line by line. 1. 2. We ran our command in Terminal to run the ex1.rb script. Ruby tells us that the le ex1.rb has an error on line 3. The type of error is ”syntax error,” and then some programmer jargon you can usually ignore. 3. It prints the offending line of code for us to see. WARNING! If you are from another country, and you get errors about ASCII encodings, then put this at the top of your Ruby scripts: # −*− coding: utf−8 −*− It will x them so that you can use Unicode UTF-8 in your scripts without a problem. Study Drills The Study Drills contain things you should try to do. If you can’t, skip it and come back later. For this exercise, try these things: 1. Make your script print another line. 2. Make your script print only one of the lines. 3. Put a # (octothorpe) character at the beginning of a line. What did it do? Try to nd out what this character does. From now on, I won’t explain how each exercise works unless an exercise is different. NOTE: An ”octothorpe” is also called a ”pound,” ”hash,” ”mesh,” or any number of names. Pick the one that makes you chill out. “Shaw_Ex01” — 2014/11/7 — 14:08 — page 17 — #6 A GOOD FIRST PROGRAM 17 Common Student Questions These are actual questions that real students have asked when doing this exercise. How do you get colors in your editor? Save your le rst as a .rb le, such as ex1.rb. Then you’ll have color when you type. I get ruby: No such file or directory – ex1.rb (LoadError). You need to be in the same directory as the le you created. Make sure you use the cd command to go there rst. For example, if you saved your le in lrthw/ex1.rb, then you would type cd lrthw/ before trying to run ruby ex1.rb. If you don’t know what any of that means, then go through Appendix A. “Shaw_Ex02” — 2014/11/7 — 14:10 — page 18 — #1 18 EXERCISE 2 Comments and Pound Characters C omments are very important in your programs. They are used to tell you what something does in English, and they are used to disable parts of your program if you need to remove them temporarily. Here’s how you use comments in Ruby: 1 2 3 4 5 6 7 8 9 # A comment, this is so you can read your program later. # Anything after the # is ignored by ruby. ex2.rb puts "I could have code like this." # and the comment after is ignored # You can also use a comment to "disable" or comment out a piece of code: # puts "This won't run." puts "This will run." From now on, I’m going to write code like this. It is important for you to understand that everything does not have to be literal. Your screen and program may visually look different, but what’s important is the text you type into the le you’re writing in your text editor. In fact, I could work with any text editor and the results would be the same. What You Should See $ ruby ex2.rb I could have code like this. This will run. Exercise 2 Session Again, I’m not going to show you screenshots of all the Terminals possible. You should understand that the above is not a literal translation of what your output should look like visually, but the text between the rst $ ruby ... and last $ lines will be what you focus on. Study Drills 1. Find out if you were right about what the # character does and make sure you know what it’s called (octothorpe or pound character). 2. Take your ex2.rb le and review each line going backward. Start at the last line, and check each word in reverse against what you should have typed. “Shaw_Ex02” — 2014/11/7 — 14:10 — page 19 — #2 COMMENTS AND POUND CHARACTERS 19 3. Did you nd more mistakes? Fix them. 4. Read what you typed out loud, including saying each character by its name. Did you nd more mistakes? Fix them. Common Student Questions Are you sure # is called the pound character? I call it the octothorpe because that is the only name that no country uses, and that works in every country. Every country thinks its name for this one character is both the most important way to do it and the only way it’s done. To me, this is simply arrogance and, really, y’all should just chill out and focus on more important things like learning to code. If # is for comments, then how come # -*- coding: utf-8 -*- works? Ruby still ignores that as code, but it’s used as a kind of ”hack” or workaround for problems with setting and detecting the format of a le. You will also nd a similar kind of comment for editor settings. Why does the # in puts "Hi # there." not get ignored? The # in that code is inside a string, so it will be put into the string until the ending " character is hit. These pound characters are just considered characters and aren’t considered comments. How do I comment out multiple lines? Put a # in front of each one. I can’t gure out how to type a # character on my country’s keyboard. Some countries use the Alt key and combinations of other keys to print characters foreign to their language. You’ll have to look online in a search engine to see how to type it. Why do I have to read code backward? It’s a trick to make your brain not attach meaning to each part of the code, and doing that makes you process each piece exactly. This catches errors and is a handy error-checking technique. This page intentionally left blank “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 249 — #1 249 APPENDIX Command Line Crash Course T his appendix is a quick, super-fast course in using the command line. It is intended to be done rapidly in about a day or two, and is not meant to teach you advanced shell usage. Introduction: Shut Up and Shell This appendix is a crash course in using the command line to make your computer perform tasks. As a crash course, it’s not as detailed or extensive as my other books. It is simply designed to get you barely capable enough to start using your computer like a real programmer does. When you’re done with this appendix, you will be able to give most of the basic commands that every shell user touches every day. You’ll understand the basics of directories and a few other concepts. The only piece of advice I am going to give you is this: Shut up and type all of this in. Sorry to be mean, but that’s what you have to do. If you have an irrational fear of the command line, the only way to conquer an irrational fear is to just shut up and ght through it. You are not going to destroy your computer. You are not going to be thrown into some jail at the bottom of Microsoft’s Redmond campus. Your friends won’t laugh at you for being a nerd. Simply ignore any stupid weird reasons you have for fearing the command line. Why? Because if you want to learn to code, then you must learn this. Programming languages are advanced ways to control your computer with language. The command line is the little baby brother of programming languages. Learning the command line teaches you to control the computer using language. Once you get past that, you can then move on to writing code and feeling like you actually own the hunk of metal you just bought. How to Use This Appendix The best way to use this appendix is to do the following: • Get yourself a small paper notebook and a pen. • Start at the beginning of the appendix and do each exercise exactly as you’re told. • When you read something that doesn’t make sense or that you don’t understand, write it down in your notebook. Leave a little space so you can write an answer. “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 250 — #2 250 LEARN RUBY THE HARD WAY • After you nish an exercise, go back through your notebook and review the questions you have. Try to answer them by searching online and asking friends who might know the answer. Email me at [email protected] and I’ll help you, too. Just keep going through this process of doing an exercise, writing down questions you have, then going back through and answering the questions you can. By the time you’re done, you’ll actually know a lot more than you think about using the command line. You Will Be Memorizing Things I’m warning you ahead of time that I’m going to make you memorize things right away. This is the quickest way to get you capable at something, but for some people memorization is painful. Just ght through it and do it anyway. Memorization is an important skill in learning things, so you should get over your fear of it. Here’s how you memorize things: • Tell yourself you will do it. Don’t try to nd tricks or easy ways out of it, just sit down and do it. • Write what you want to memorize on some index cards. Put one half of what you need to learn on one side, then the other half on the other side. • Every day for about 15–30 minutes, drill yourself on the index cards, trying to recall each one. Put any cards you don’t get right into a different pile, just drill those cards until you get bored, and then try the whole deck and see if you improve. • Before you go to bed, drill just the cards you got wrong for about 5 minutes, then go to sleep. There are other techniques, like you can write what you need to learn on a sheet of paper, laminate it, then stick it to the wall of your shower. While you’re bathing, drill the knowledge without looking, and when you get stuck glance at it to refresh your memory. If you do this every day, you should be able to memorize most of the things I tell you to memorize in about a week to a month. Once you do, nearly everything else becomes easier and intuitive, which is the purpose of memorization. It’s not to teach you abstract concepts, but rather to ingrain the basics so that they are intuitive and you don’t have to think about them. Once you’ve memorized these basics, they stop being speed bumps preventing you from learning more advanced abstract concepts. “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 251 — #3 COMMAND LINE CRASH COURSE 251 The Setup In this appendix you will be instructed to do three things: • Do some things in your shell (command line, Terminal, PowerShell). • Learn about what you just did. • Do more on your own. For this rst exercise, you’ll be expected to get your Terminal open and working so that you can do the rest of the appendix. Do This Get your Terminal, shell, or PowerShell working so you can access it quickly and know that it works. Mac OS X For Mac OS X you’ll need to do this: • Hold down the command key and hit the spacebar. • In the top right corner, the blue ”search bar” will pop up. • Type: terminal • Click on the Terminal application that looks kind of like a black box. • This will open Terminal. • You can now go to your dock and CTRL-click to pull up the menu, then select Options->Keep In dock. Now you have your Terminal open and it’s in your dock so you can get to it. Linux I’m assuming that if you have Linux, then you already know how to get at your Terminal. Look through the menu for your window manager for anything named ”Shell” or ”Terminal.” “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 252 — #4 252 LEARN RUBY THE HARD WAY Windows On Windows, we’re going to use PowerShell. People used to work with a program called cmd.exe, but it’s not nearly as usable as PowerShell. If you have Windows 7 or later, do this: • Click Start. • In ”Search programs and les” type: powershell • Hit Enter. If you don’t have Windows 7, you should seriously consider upgrading. If you still insist on not upgrading then you can try installing it from Microsoft’s download center. Search online to nd ”powershell downloads” for your version of Windows. You are on your own, though, since I don’t have Windows XP, but hopefully the PowerShell experience is the same. You Learned This You learned how to get your Terminal open, so you can do the rest of this appendix. WARNING! If you have that really smart friend who already knows Linux, ignore him when he tells you to use something other than bash. I’m teaching you bash. That’s it. He will claim that zsh will give you 30 more IQ points and win you millions in the stock market. Ignore him. Your goal is to get capable enough and at this level it doesn’t matter which shell you use. The next warning is stay off IRC or other places where ”hackers” hang out. They think it’s funny to hand you commands that can destroy your computer. The command rm -rf / is a classic that you must never type. Just avoid them. If you need help, make sure you get it from someone you trust and not from random idiots on the Internet. Do More This exercise has a large ”do more” part. The other exercises are not as involved as this one, but I’m having you prime your brain for the rest of the appendix by doing some memorization. Just trust me: this will make things silky smooth later on. Linux/Mac OS X Take this list of commands and create index cards with the names on the left on one side, and the de nitions on the other side. Drill them every day while continuing with the lessons in this appendix. “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 253 — #5 COMMAND LINE CRASH COURSE pwd print working directory hostname mkdir my computer’s network name make directory cd change directory ls list directory rmdir remove directory pushd push directory popd pop directory cp copy a le or directory mv move a le or directory less page through a le cat print the whole le xargs execute arguments nd nd les grep nd things inside les man read a manual page apropos env look at your environment echo print some arguments export exit sudo nd which man page is appropriate export/set a new environment variable exit the shell DANGER! become super user root DANGER! Windows If you’re using Windows, then here’s your list of commands: pwd print working directory hostname mkdir my computer’s network name make directory 253 “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 254 — #6 254 LEARN RUBY THE HARD WAY cd change directory ls list directory rmdir remove directory pushd push directory popd cp pop directory copy a le or directory robocopy mv move a le or directory more type robust copy page through a le print the whole le for les run a command on lots of les dir -r nd les select-string help read a manual page helpctr echo set exit runas nd things inside les nd which manual page is appropriate print some arguments export/set a new environment variable exit the shell DANGER! become super user root DANGER! Drill, drill, drill! Drill until you can say these phrases right away when you see that word. Then drill the inverse, so that you read the phrase and know which command will do that. You’re building your vocabulary by doing this, but don’t spend so much time you go nuts and get bored. Paths, Folders, and Directories (pwd) In this exercise you learn how to print your working directory with the pwd command. “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 255 — #7 COMMAND LINE CRASH COURSE 255 Do This I’m going to teach you how to read these ”sessions” that I show you. You don’t have to type everything I list here, just some of the parts: You do not type in the $ (UNIX) or > (Windows). That’s just me showing you my session • so you can see what I got. You type in the stuff after $ or >, then hit Enter. So if I have $ pwd, you type just pwd • and hit Enter. You can then see what I have for output followed by another $ or > prompt. That content • is the output and you should see the same output. Let’s do a simple rst command so you can get the hang of this: Linux/OS X $ pwd Exercise 2 Session /Users/zedshaw $ Windows PS C:\Users\zed> pwd Exercise 2 Windows Session Path ---- C:\Users\zed PS C:\Users\zed> WARNING! In this appendix I need to save space so that you can focus on the important details of the commands. To do this, I’m going to strip out the rst part of the prompt (the PS C:\Users\zed above) and leave just the little > part. This means your prompt won’t look exactly the same, but don’t worry about that. Remember that from now on I’ll include only the > to tell you that’s the prompt. I’m doing the same thing for the UNIX prompts, but UNIX prompts are so varied that most people get used to $ meaning ”just the prompt.” “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 256 — #8 256 LEARN RUBY THE HARD WAY You Learned This Your prompt will look different from mine. You may have your user name before the $ and the name of your computer. On Windows it will probably look different, too. The key is that you see this pattern: • There’s a prompt. • You type a command there. In this case, it’s pwd. • It printed something. • Repeat. You just learned what pwd does, which means ”print working directory.” What’s a directory? It’s a folder. Folder and directory are the same thing, and they’re used interchangeably. When you open your le browser on your computer to graphically nd les, you are walking through folders. Those folders are the exact same things as these ”directories” we’re going to work with. Do More • • Type pwd 20 times and each time say ”print working directory.” Write down the path that this command gives you. Find it with your graphical le browser of choice. • No, seriously, type it 20 times and say it out loud. Sssh. Just do it. If You Get Lost As you go through these instructions, you may get lost. You may not know where you are or where a le is and have no idea how to continue. To solve this problem, I am going to teach you the commands to type to stop being lost. Whenever you get lost, it is most likely because you were typing commands and have no idea where you’ve ended up. What you should do is type pwd to print your current directory. This tells you where you are. The next thing you need is a way of getting back to where you are safe, your home. To do this, type cd ~ and you are back in your home. “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 257 — #9 COMMAND LINE CRASH COURSE 257 This means if you get lost at any time, you should type: pwd cd ~ The rst command pwd tells you where you are. The second command cd ~ takes you home so you can try again. Do This Right now gure out where you are, and then go home using pwd and cd ~. This will ensure that you are always in the right place. You Learned This How to get back to your home if you ever get lost. Make a Directory (mkdir) In this exercise you learn how to make a new directory (folder) using the mkdir command. Do This Remember! You need to go home rst! Do your pwd and then cd ~ before doing this exercise. Before you do all exercises in this appendix, always go home rst! Linux/OS X $ pwd $ cd ~ $ mkdir temp $ mkdir temp/stuff $ mkdir temp/stuff/things $ mkdir -p temp/stuff/things/frank/joe/alex/john $ Exercise 4 Session “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 258 — #10 258 LEARN RUBY THE HARD WAY Windows Exercise 4 Windows Session > pwd > cd ~ > mkdir temp Directory: C:\Users\zed Mode ---- d---- LastWriteTime ------------- 12/17/2011 9:02 AM Length Name ------ ---temp > mkdir temp/stuff Directory: C:\Users\zed\temp Mode ---- d---- LastWriteTime ------------- 12/17/2011 9:02 AM Length Name ------ ---- stuff > mkdir temp/stuff/things Directory: C:\Users\zed\temp\stuff Mode ---- d---- LastWriteTime ------------- 12/17/2011 9:03 AM Length Name ------ ---- things > mkdir temp/stuff/things/frank/joe/alex/john “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 259 — #11 COMMAND LINE CRASH COURSE 259 Directory: C:\Users\zed\temp\stuff\things\frank\joe\alex Mode ---- d---- LastWriteTime ------------- 12/17/2011 9:03 AM Length Name ------ ---john > This is the only time I’ll list the pwd and cd ~ commands. They are expected in the exercises every time. Do them all the time. You Learned This Now we get into typing more than one command. These are all the different ways you can run mkdir. What does mkdir do? It make directories. Why are you asking that? You should be doing your index cards and getting your commands memorized. If you don’t know that ”mkdir makes directories,” then keep working the index cards. What does it mean to make a directory? You might call directories ”folders.” They’re the same thing. All you did in this exercise is create directories inside directories inside of more directories. This is called a ”path” and it’s a way of saying ” rst temp, then stuff, then things, and that’s where I want it.” It’s a set of directions to the computer of where you want to put something in the tree of folders (directories) that make up your computer’s hard disk. WARNING! In this appendix I’m using the / (slash) character for all paths since it works the same on all computers now. However, Windows users need to know that you can also use the \ (backslash) character and other Windows users will expect that at times. Do More • The concept of a ”path” might confuse you at this point. Don’t worry. We’ll do a lot more with them and then you’ll get it. • Make 20 other directories inside the temp directory in various levels. Go look at them with a graphical le browser. • • Make a directory with a space in the name by putting quotes around it: mkdir "I Have Fun" If the temp directory already exists, then you’ll get an error. Use cd to change to a work directory that you can control and try it there. On Windows, Desktop is a good place. “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 260 — #12 260 LEARN RUBY THE HARD WAY Change Directory (cd) In this exercise you learn how to change from one directory to another using the cd command. Do This I’m going to give you the instructions for these sessions one more time: • • You do not type in the $ (UNIX) or > (Windows). You type in the stuff after this, then hit Enter. If I have $ cd temp you just type cd temp and hit Enter. • • The output comes after you hit Enter, followed by another $ or > prompt. Always go home rst! Do pwd and then cd ~ so you go back to your starting point. Linux/OS X $ cd temp $ pwd ~/temp $ cd stuff $ pwd ~/temp/stuff $ cd things $ pwd ~/temp/stuff/things $ cd frank/ $ pwd ~/temp/stuff/things/frank $ cd joe/ $ pwd ~/temp/stuff/things/frank/joe $ cd alex/ $ pwd ~/temp/stuff/things/frank/joe/alex $ cd john/ $ pwd ~/temp/stuff/things/frank/joe/alex/john Exercise 5 Session “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 261 — #13 COMMAND LINE CRASH COURSE 261 $ cd .. $ cd .. $ pwd ~/temp/stuff/things/frank/joe $ cd .. $ cd .. $ pwd ~/temp/stuff/things $ cd ../../.. $ pwd ~/ $ cd temp/stuff/things/frank/joe/alex/john $ pwd ~/temp/stuff/things/frank/joe/alex/john $ cd ../../../../../../../ $ pwd ~/ $ Windows > cd temp > pwd Path ---- C:\Users\zed\temp > cd stuff > pwd Path ---- C:\Users\zed\temp\stuff > cd things Exercise 5 Windows Session “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 262 — #14 262 LEARN RUBY THE HARD WAY > pwd Path ---- C:\Users\zed\temp\stuff\things > cd frank > pwd Path ---- C:\Users\zed\temp\stuff\things\frank > cd joe > pwd Path ---- C:\Users\zed\temp\stuff\things\frank\joe > cd alex > pwd Path ---- C:\Users\zed\temp\stuff\things\frank\joe\alex > cd john > pwd Path ---- C:\Users\zed\temp\stuff\things\frank\joe\alex\john > cd .. “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 263 — #15 COMMAND LINE CRASH COURSE 263 > cd .. > cd .. > pwd Path ---- C:\Users\zed\temp\stuff\things\frank > cd ../.. > pwd Path ---- C:\Users\zed\temp\stuff > cd .. > cd .. > cd temp/stuff/things/frank/joe/alex/john > cd ../../../../../../../ > pwd Path ---- C:\Users\zed > You Learned This You made all these directories in the last exercise, and now you’re just moving around inside them with the cd command. In my session, I also use pwd to check where I am, so remember not to type the output that pwd prints. For example, on line 3 you see ~/temp but that’s the output of pwd from the prompt above it. Do not type this in. You should also see how I use the .. to move ”up” in the tree and path. “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 264 — #16 264 LEARN RUBY THE HARD WAY Do More A very important part of learning to use the command line interface (CLI) on a computer with a graphical user interface (GUI) is guring out how they work together. When I started using computers, there was no ”GUI” and you did everything with the DOS prompt (the CLI). Later, when computers became powerful enough that everyone could have graphics, it was simple for me to match CLI directories with GUI windows and folders. Most people today, however, have no comprehension of the CLI, paths, and directories. In fact, it’s very dif cult to teach it to them and the only way to learn about the connection is for you to constantly work with the CLI until one day it clicks that things you do in the GUI will show up in the CLI. The way you do this is by spending some time nding directories with your GUI le browser, then going to them with your CLI. This is what you’ll do next. • • • • cd to the joe directory with one command. cd back to temp with one command, but not further above that. Find out how to cd to your ”home directory” with one command. cd to your Documents directory, then nd it with your GUI le browser (e.g., Finder, Windows Explorer, etc.). • • • cd to your Downloads directory, then nd it with your le browser. Find another directory with your le browser, then cd to it. Remember when you put quotes around a directory with spaces in it? You can do that with any command. For example, if you have a directory I Have Fun, then you can do: cd "I Have Fun" List Directory (ls) In this exercise you learn how to list the contents of a directory with the ls command. Do This Before you start, make sure you cd back to the directory above temp. If you have no idea where you are, use pwd to gure it out and then move there. “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 265 — #17 COMMAND LINE CRASH COURSE Linux/OS X $ cd temp 265 Exercise 6 Session $ ls stuff $ cd stuff $ ls things $ cd things $ ls frank $ cd frank $ ls joe $ cd joe $ ls alex $ cd alex $ ls $ cd john $ ls $ cd .. $ ls john $ cd ../../../ $ ls frank $ cd ../../ $ ls stuff $ Windows > cd temp > ls Exercise 6 Windows Session “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 266 — #18 266 LEARN RUBY THE HARD WAY Directory: C:\Users\zed\temp Mode ---- d---- LastWriteTime ------------- 12/17/2011 9:03 AM Length Name ------ ---- stuff > cd stuff > ls Directory: C:\Users\zed\temp\stuff Mode ---- d---- LastWriteTime ------------- 12/17/2011 9:03 AM Length Name ------ ---- things > cd things > ls Directory: C:\Users\zed\temp\stuff\things Mode ---- d---> cd frank > ls LastWriteTime ------------- 12/17/2011 9:03 AM Length Name ------ ---- frank “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 267 — #19 COMMAND LINE CRASH COURSE Directory: C:\Users\zed\temp\stuff\things\frank Mode ---- d---- LastWriteTime ------------- 12/17/2011 9:03 AM Length Name ------ ---joe > cd joe > ls Directory: C:\Users\zed\temp\stuff\things\frank\joe Mode ---- d---- LastWriteTime ------------- 12/17/2011 9:03 AM Length Name ------ ---alex > cd alex > ls Directory: C:\Users\zed\temp\stuff\things\frank\joe\alex Mode ---- d---> cd john > ls > cd .. > ls LastWriteTime ------------- 12/17/2011 9:03 AM Length Name ------ ---john 267 “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 268 — #20 268 LEARN RUBY THE HARD WAY Directory: C:\Users\zed\temp\stuff\things\frank\joe\alex Mode ---- d---- LastWriteTime ------------- 12/17/2011 9:03 AM Length Name ------ ---john > cd .. > ls Directory: C:\Users\zed\temp\stuff\things\frank\joe Mode ---- d---- LastWriteTime ------------- 12/17/2011 9:03 AM Length Name ------ ---alex > cd ../../.. > ls Directory: C:\Users\zed\temp\stuff Mode ---- d---> cd .. > ls LastWriteTime ------------- 12/17/2011 9:03 AM Length Name ------ ---- things “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 269 — #21 COMMAND LINE CRASH COURSE 269 Directory: C:\Users\zed\temp Mode ---- d---- LastWriteTime ------------- 12/17/2011 9:03 AM Length Name ------ ---- stuff > You Learned This The ls command lists out the contents of the directory you are currently in. You can see me use cd to change into different directories and then list what’s in them so I know which directory to go to next. There are a lot of options for the ls command, but you’ll learn how to get help on those later when we cover the help command. Do More • Type every one of these commands in! You have to actually type these to learn them. Just reading them is not good enough. I’ll stop yelling now. • • • On UNIX, try the ls -lR command while you’re in temp. On Windows, do the same thing with dir -R. Use cd to get to other directories on your computer and then use ls to see what’s in them. • Update your notebook with new questions. I know you probably have some, because I’m not covering everything about this command. • Remember that if you get lost, then use ls and pwd to gure out where you are, then go to where you need to be with cd. Remove Directory (rmdir) In this exercise you learn how to remove an empty directory. “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 270 — #22 270 LEARN RUBY THE HARD WAY Do This Linux/OS X $ cd temp Exercise 7 Session $ ls stuff $ cd stuff/things/frank/joe/alex/john/ $ cd .. $ rmdir john $ cd .. $ rmdir alex $ cd .. $ ls joe $ rmdir joe $ cd .. $ ls frank $ rmdir frank $ cd .. $ ls things $ rmdir things $ cd .. $ ls stuff $ rmdir stuff $ pwd ~/temp $ WARNING! If you try to do rmdir on Mac OS X and it refuses to remove the directory even though you are positive it’s empty, then there is actually a le in there called .DS_Store. In that case, type rm -rf <dir> instead (replace <dir> with the directory name). “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 271 — #23 COMMAND LINE CRASH COURSE Windows Exercise 7 Windows Session > cd temp > ls Directory: C:\Users\zed\temp Mode ---- d---- LastWriteTime ------------- 12/17/2011 9:03 AM Length Name ------ ---- stuff > cd stuff/things/frank/joe/alex/john/ > cd .. > rmdir john > cd .. > rmdir alex > cd .. > rmdir joe > cd .. > rmdir frank > cd .. > ls Directory: C:\Users\zed\temp\stuff Mode ---- d---- LastWriteTime > ls ------------- 12/17/2011 > rmdir things > cd .. 271 9:14 AM Length Name ------ ---- things “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 272 — #24 272 LEARN RUBY THE HARD WAY Directory: C:\Users\zed\temp Mode ---- d---- LastWriteTime ------------- 12/17/2011 9:14 AM Length Name ------ ---- stuff > rmdir stuff > pwd Path ---- C:\Users\zed\temp > cd .. > You Learned This I’m now mixing up the commands so make sure you type them exactly and pay attention. Every time you make a mistake, it’s because you aren’t paying attention. If you nd yourself making many mistakes, then take a break or just quit for the day. You’ve always got tomorrow to try again. In this example you’ll learn how to remove a directory. It’s easy. You just go to the directory right above it, then type rmdir <dir>, replacing <dir> with the name of the directory to remove. Do More • Make 20 more directories and remove them all. • Make a single path of directories that is 10 deep and remove them one at a time just like I did. • If you try to remove a directory with content you will get an error. I’ll show you how to remove these in later exercises. “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 273 — #25 COMMAND LINE CRASH COURSE 273 Moving Around (pushd, popd) In this exercise you learn how to save your current location and go to a new location with pushd. You then learn how to return to the saved location with popd. Do This Linux/OS X $ cd temp $ mkdir -p i/like/icecream $ pushd i/like/icecream ~/temp/i/like/icecream ~/temp $ popd ~/temp $ pwd ~/temp $ pushd i/like ~/temp/i/like ~/temp $ pwd ~/temp/i/like $ pushd icecream ~/temp/i/like/icecream ~/temp/i/like ~/temp $ pwd ~/temp/i/like/icecream $ popd ~/temp/i/like ~/temp $ pwd ~/temp/i/like $ popd ~/temp $ pushd i/like/icecream ~/temp/i/like/icecream ~/temp $ pushd ~/temp ~/temp/i/like/icecream $ pwd ~/temp $ pushd Exercise 8 Session “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 274 — #26 274 LEARN RUBY THE HARD WAY ~/temp/i/like/icecream ~/temp $ pwd ~/temp/i/like/icecream $ Windows Exercise 8 Windows Session > cd temp > mkdir -p i/like/icecream Directory: C:\Users\zed\temp\i\like Mode ---- d---- LastWriteTime ------------- 12/20/2011 > pushd i/like/icecream > popd > pwd Path ---- C:\Users\zed\temp > pushd i/like > pwd Path ---- C:\Users\zed\temp\i\like > pushd icecream > pwd 11:05 AM Length Name ------ ---- icecream “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 275 — #27 COMMAND LINE CRASH COURSE 275 Path ---- C:\Users\zed\temp\i\like\icecream > popd > pwd Path ---- C:\Users\zed\temp\i\like > popd > You Learned This You’re getting into programmer territory with these commands, but they’re so handy I have to teach them to you. These commands let you temporarily go to a different directory and then come back, easily switching between the two. The pushd command takes your current directory and ”pushes” it into a list for later, then it changes to another directory. It’s like saying, ”Save where I am, then go here.” The popd command takes the last directory you pushed and ”pops” it off, taking you back there. Finally, on UNIX, the command pushd, if you run it by itself with no arguments, will switch between your current directory and the last one you pushed. It’s an easy way to switch between two directories. This does not work in PowerShell. Do More • • Use these commands to move around directories all over your computer. Remove the i/like/icecream directories and make your own, then move around in them. • Explain to yourself the output that pushd and popd will print out for you. Notice how it works like a stack? “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 276 — #28 276 LEARN RUBY THE HARD WAY You already know this, but remember that mkdir -p will make an entire path even if all • the directories don’t exist. That’s what I did very rst for this exercise. Making Empty Files (Touch, New-Item) In this exercise you learn how to make an empty command. le using the touch (new-item on Windows) Do This Linux/OS X Exercise 9 Session $ cd temp $ touch iamcool.txt $ ls iamcool.txt $ Windows Exercise 9 Windows Session > cd temp > New-Item iamcool.txt -type file > ls Directory: C:\Users\zed\temp Mode ---- -a--> LastWriteTime ------------- 12/17/2011 9:03 AM Length Name ------ ---- iamcool.txt “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 277 — #29 COMMAND LINE CRASH COURSE 277 You Learned This You learned how to make an empty le. On UNIX touch does this, and it also changes the times on the le. I rarely use it for anything other than making empty les. On Windows, you don’t have this command, so you learned how to use the New-Item command, which does the same thing but can also make new directories. Do More • UNIX: Make a directory, change to it, and then make a le in it. Then move up one level and run the rmdir command in this directory. You should get an error. Try to understand why you got this error. • Windows: Do the same thing, but you won’t get an error. You’ll get a prompt asking if you really want to remove the directory. Copy a File (cp) In this exercise you learn how to copy a le from one location to another with the cp command. Do This Linux/OS X Exercise 10 Session $ cd temp $ cp iamcool.txt neat.txt $ ls iamcool.txt neat.txt $ cp neat.txt awesome.txt $ ls awesome.txt iamcool.txt neat.txt $ cp awesome.txt thefourthfile.txt $ ls awesome.txt iamcool.txt $ mkdir something neat.txt thefourthfile.txt $ cp awesome.txt something/ $ ls awesome.txt iamcool.txt neat.txt something thefourthfile.txt “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 278 — #30 278 LEARN RUBY THE HARD WAY $ ls something/ awesome.txt $ cp -r something newplace $ ls newplace/ awesome.txt $ Windows Exercise 10 Windows Session > cd temp > cp iamcool.txt neat.txt > ls Directory: C:\Users\zed\temp Mode ---- -a---a--- LastWriteTime ------------- 12/22/2011 12/22/2011 4:49 PM 4:49 PM Length Name ------ ---- 0 iamcool.txt 0 neat.txt > cp neat.txt awesome.txt > ls Directory: C:\Users\zed\temp Mode ---- LastWriteTime ------------- -a--- 12/22/2011 4:49 PM -a--- 12/22/2011 4:49 PM -a--- 12/22/2011 4:49 PM > cp awesome.txt thefourthfile.txt > ls Length Name ------ ---- 0 awesome.txt 0 iamcool.txt 0 neat.txt “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 279 — #31 COMMAND LINE CRASH COURSE Directory: C:\Users\zed\temp Mode ---- LastWriteTime ------------- -a--- 12/22/2011 4:49 PM -a--- 12/22/2011 4:49 PM -a---a--- 12/22/2011 12/22/2011 4:49 PM 4:49 PM Length Name ------ ---- 0 awesome.txt 0 iamcool.txt 0 neat.txt 0 thefourthfile.txt > mkdir something Directory: C:\Users\zed\temp Mode ---- d---- LastWriteTime ------------- 12/22/2011 4:52 PM Length Name ------ ---- something > cp awesome.txt something/ > ls Directory: C:\Users\zed\temp Mode ---- LastWriteTime ------------- d---- 12/22/2011 4:52 PM -a--- 12/22/2011 4:49 PM -a---a---a--- 12/22/2011 12/22/2011 12/22/2011 > ls something Length Name ------ ---- something 4:49 PM 0 awesome.txt 4:49 PM 0 neat.txt 4:49 PM 0 iamcool.txt 0 thefourthfile.txt 279 “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 280 — #32 280 LEARN RUBY THE HARD WAY Directory: C:\Users\zed\temp\something Mode ---- -a--- LastWriteTime ------------- 12/22/2011 4:49 PM Length Name ------ ---- 0 awesome.txt > cp -recurse something newplace > ls newplace Directory: C:\Users\zed\temp\newplace Mode ---- -a--- LastWriteTime ------------- 12/22/2011 4:49 PM Length Name ------ ---- 0 awesome.txt > You Learned This Now you can copy les. It’s simple to just take a le and copy it to a new one. In this exercise I also make a new directory and copy a le into that directory. I’m going to tell you a secret about programmers and system administrators now: they are lazy. I’m lazy. My friends are lazy. That’s why we use computers. We like to make computers do boring things for us. In the exercises so far you have been typing repetitive boring commands so that you can learn them, but usually it’s not like this. Usually if you nd yourself doing something boring and repetitive, there’s probably a programmer who has gured out how to make it easier. You just don’t know about it. The other thing about programmers is they aren’t nearly as clever as you think. If you overthink what to type, then you’ll probably get it wrong. Instead, try to imagine what the name of a command is and try it. Chances are that it’s a name or some abbreviation similar to what you thought it was. If you still can’t gure it out intuitively, then ask around and search online. Hopefully it’s not something really stupid like ROBOCOPY. “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 281 — #33 COMMAND LINE CRASH COURSE 281 Do More • Use the cp -r command to copy more directories with les in them. • Copy a le to your home directory or desktop. • Find these les in your graphical user interface and open them in a text editor. Notice how sometimes I put a / (slash) at the end of a directory? That makes sure the le • is really a directory, so if the directory doesn’t exist I’ll get an error. Moving a File (mv) In this exercise you learn how to move a le from one location to another using the mv command. Do This Linux/OS X Exercise 11 Session $ cd temp $ mv awesome.txt uncool.txt $ ls newplace uncool.txt $ mv newplace oldplace $ ls oldplace uncool.txt $ mv oldplace newplace $ ls newplace $ uncool.txt Windows > cd temp > mv awesome.txt uncool.txt > ls Exercise 11 Windows Session “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 282 — #34 282 LEARN RUBY THE HARD WAY Directory: C:\Users\zed\temp Mode ---- LastWriteTime ------------- Length Name ------ ---- d---- 12/22/2011 4:52 PM -a--- 12/22/2011 4:49 PM 0 iamcool.txt 4:49 PM 0 thefourthfile.txt d----a---a---a--- 12/22/2011 12/22/2011 12/22/2011 12/22/2011 4:52 PM 4:49 PM 4:49 PM newplace something 0 neat.txt 0 uncool.txt > mv newplace oldplace > ls Directory: C:\Users\zed\temp Mode ---- LastWriteTime ------------- Length Name ------ ---- d---- 12/22/2011 4:52 PM -a--- 12/22/2011 4:49 PM 0 iamcool.txt 4:49 PM 0 thefourthfile.txt d----a---a---a--- 12/22/2011 12/22/2011 12/22/2011 12/22/2011 > mv oldplace newplace > ls newplace 4:52 PM 4:49 PM 4:49 PM oldplace something 0 neat.txt 0 uncool.txt “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 283 — #35 COMMAND LINE CRASH COURSE 283 Directory: C:\Users\zed\temp\newplace Mode ---- -a--- LastWriteTime ------------- 12/22/2011 4:49 PM Length Name ------ ---- 0 awesome.txt > ls Directory: C:\Users\zed\temp Mode ---- LastWriteTime ------------- Length Name ------ ---- d---- 12/22/2011 4:52 PM -a--- 12/22/2011 4:49 PM 0 iamcool.txt 4:49 PM 0 thefourthfile.txt d----a---a---a--- 12/22/2011 12/22/2011 12/22/2011 12/22/2011 4:52 PM 4:49 PM 4:49 PM newplace something 0 neat.txt 0 uncool.txt > You Learned This Moving les or, rather, renaming them. It’s easy: give the old name and the new name. Do More • Move a le in the newplace directory to another directory, then move it back. View a File (less, MORE) To do this exercise you’re going to do some work using the commands you know so far. You’ll also need a text editor that can make plain text (.txt) les. Here’s what you do: • Open your text editor and type some stuff into a new le. On OS X this could be TextWrangler. On Windows this might be Notepad++. On Linux this could be gedit. Any editor will work. “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 284 — #36 284 LEARN RUBY THE HARD WAY Save that le to your desktop and name it test.txt. • • In your shell use the commands you know to copy this le to your temp directory that you’ve been working with. Once you’ve done that, complete this exercise. Do This Linux/OS X Exercise 12 Session $ less test.txt [displays file here] $ That’s it. To get out of less, just type q (as in quit). Windows > more test.txt Exercise 12 Windows Session [displays file here] > WARNING! In the output I’m showing [displays file here] to ”abbreviate” what that program shows. I’ll do this when I mean to say, ”Showing you the output of this program is too complex, so just insert what you see on your computer here and pretend I did show it to you.” Your screen will not actually show this. You Learned This This is one way to look at the contents of a le. It’s useful because, if the le has many lines, it will ”page” so that only one screenful at a time is visible. In the Do More section, you’ll play with this some more. Do More • Open your text le again and repeatedly copy-paste the text so that it’s about 50–100 lines long. • Copy it to your temp directory again so you can look at it. “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 285 — #37 COMMAND LINE CRASH COURSE • 285 Now do the exercise again, but this time page through it. On UNIX you use the spacebar and w (the letter w) to go down and up. Arrow keys also work. On Windows, just hit the spacebar to page through. • Look at some of the empty les you created. • The cp command will overwrite les that already exist, so be careful when copying les around. Stream a File (cat) You’re going to do some more setup for this one so you get used to making les in one program and then accessing them from the command line. With the same text editor from the last exercise, create another le named test2.txt but this time save it directly to your temp directory. Do This Linux/OS X $ less test2.txt Exercise 13 Session [displays file here] $ cat test2.txt I am a fun guy. Don't you know why? Because I make poems, that make babies cry. $ cat test.txt Hi there this is cool. $ Windows > more test2.txt [displays file here] > cat test2.txt I am a fun guy. Don't you know why? Exercise 13 Windows Session “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 286 — #38 286 LEARN RUBY THE HARD WAY Because I make poems, that make babies cry. > cat test.txt Hi there this is cool. > Remember that when I say [displays file here], I’m abbreviating the output of that command so I don’t have to show you exactly everything. You Learned This Do you like my poem? Totally going to win a Nobel. Anyway, you already know the rst command, and I’m just having you check that your le is there. Then you cat the le to the screen. This command spews the whole le to the screen with no paging or stopping. To demonstrate that, I have you do this to the test.txt, which should just spew a bunch of lines from that exercise. Do More • • • Make a few more text les and work with cat. UNIX: Try cat test.txt test2.txt and see what it does. Windows: Try cat test.txt,test2.txt and see what it does. Removing a File (rm) In this exercise you learn how to remove (delete) a le using the rm command. Do This Linux/OS X Exercise 14 Session $ cd temp $ ls uncool.txt iamcool.txt $ rm uncool.txt $ ls neat.txt something thefourthfile.txt “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 287 — #39 COMMAND LINE CRASH COURSE iamcool.txt neat.txt something 287 thefourthfile.txt $ rm iamcool.txt neat.txt thefourthfile.txt $ ls something $ cp -r something newplace $ $ rm something/awesome.txt $ rmdir something $ rm -rf newplace $ ls $ Windows Exercise 14 Windows Session > cd temp > ls Directory: C:\Users\zed\temp Mode ---- LastWriteTime ------------- Length Name ------ ---- d---- 12/22/2011 4:52 PM -a--- 12/22/2011 4:49 PM 0 iamcool.txt 4:49 PM 0 thefourthfile.txt d----a---a---a--- 12/22/2011 12/22/2011 12/22/2011 12/22/2011 > rm uncool.txt > ls 4:52 PM 4:49 PM 4:49 PM newplace something 0 neat.txt 0 uncool.txt “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 288 — #40 288 LEARN RUBY THE HARD WAY Directory: C:\Users\zed\temp Mode ---- LastWriteTime ------------- Length Name ------ ---- d---- 12/22/2011 4:52 PM -a--- 12/22/2011 4:49 PM 0 iamcool.txt 4:49 PM 0 thefourthfile.txt d----a---a--- 12/22/2011 12/22/2011 12/22/2011 4:52 PM 4:49 PM newplace something 0 neat.txt > rm iamcool.txt > rm neat.txt > rm thefourthfile.txt > ls Directory: C:\Users\zed\temp Mode ---- d---d---- LastWriteTime ------------- 12/22/2011 12/22/2011 4:52 PM 4:52 PM Length Name ------ ---- newplace something > cp -r something newplace > rm something/awesome.txt > rmdir something > rm -r newplace > ls > You Learned This Here we clean up the les from the last exercise. Remember when I had you try to rmdir on a directory with something in it? Well, that failed because you can’t remove a directory with les in it. Instead you have to remove the le, or recursively delete all of its contents. That’s what you did at the end of this example. “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 289 — #41 COMMAND LINE CRASH COURSE 289 Do More • Clean up everything in temp from all the exercises so far. • Write in your notebook to be careful when running recursive remove commands on les. Exiting Your Terminal (exit) Do This Linux/OS X $ exit Windows > exit Exercise 23 Session Exercise 23 Windows Session You Learned This Your nal exercise is how to exit a Terminal. Again, this is very easy, but I’m going to have you do more. Do More For your last set of exercises, I want you to use the help system to look up a set of commands you should research and learn how to use on your own. Here’s the list for UNIX: • • • • xargs sudo chmod chown “Shaw_AppendixA” — 2014/11/7 — 18:37 — page 290 — #42 290 LEARN RUBY THE HARD WAY For Windows, look up these things: • • • • forfiles runas attrib icacls Find out what these are, play with them, and then add them to your index cards. Command Line Next Steps You have completed the crash course. At this point you should be a barely capable shell user. There’s a huge list of tricks and key sequences you don’t know yet, and I’m going to give you a few nal places to go research more. UNIX Bash References The shell you’ve been using is called bash. It’s not the greatest shell but it’s everywhere and has a lot of features so it’s a good start. Here’s a short list of links about bash you should visit: Bash Cheat Sheet http://cli.learncodethehardway.org/bash_cheat_sheet.pdf created by Raph- ael and CC licensed. Reference Manual http://www.gnu.org/software/bash/manual/bashref.html PowerShell References On Windows, there’s really only PowerShell. Here’s a list of useful links related to PowerShell: Owner’s Manual Cheat Sheet http://technet.microsoft.com/en-us/library/ee221100.aspx http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=7097 Master PowerShell http://powershell.com/cs/blogs/ebook/default.aspx “Shaw_Index” — 2014/11/8 — 17:18 — page 291 — #1 291 INDEX Index Symbols " (double quotes) escaping, 38 strings and, 28, 33 variables and, 30 ' (single quotes) escaping, 38 strings and, 33 variables and, 30 " " " (triple quotes), 37–38 / (forward-slash) characters, 38–40 \ (backslash) characters, 38–40 _ (underscore) characters, 24 || (or) expressions, 91–96 += (increment by) operators, 71–72, 99 = (equal) characters == vs., 25 ARGV and, 46–51 in asking questions of users, 42 escaping quotes, 38 format strings and, 34–37 naming variables with, 24–26 printing variables with, 28–29 returning values from functions with, 74–76 setting variables to numbers, 44–45 setting variables to strings, 30–33 == (double equal) characters, 25, 92–96 ! (not) expressions, 91–96 != (not equal) characters, 91–96 # (pound) characters, 18–19 ## ?? comments, 159–161 #{} (format activators), 28, 35 % (modulus) operators, 22, 35 %{} (format activators), 35 && (and) expressions, 91–96 *args (asterisk args), 63–65 @ (object scope), 125, 149–151 [ (left bracket), opening arrays with, 106–108 ] (right bracket), closing arrays with, 106–108 > (prompts), 50–51 Numbers 2-dimensional (2D) arrays, 108 8080 port, 219–223 A Addresses, de ned, 225 Advanced user input exceptions in, 206 game lexicon and, 204–206 introduction to, 204 lexicon types in, 205 numbers in, 206 questions about, 210 sentence breaks in, 204–205 Study Drills on, 209 testing rst, 206–207 testing procedures, 207–209 writing scanners in, 205 Advice for programmers, 246–247 After inheritance, 180–182 Algorithms, 140 Analysis of game engines. See Game engine analysis of games, 188–189, 191 object-oriented. See Object-oriented analysis top down versus bottom up, 170–176 And (&&) expressions, 91–96 Argument variable (ARGV). See ARGV (argument variable) ArgumentError, 206 Arguments *args, 63–65 ARGV. See ARGV (argument variable) “Shaw_Index” — 2014/11/8 — 17:18 — page 292 — #2 292 INDEX Arguments (Continued) arrays and, 128 class style and, 189 in command line, 46–47 in functions, 62–68, 75 ARGV (argument variable) introduction to, 46–48 opening les with, 52–54 prompting and passing with, 50–51 Arrays 2-dimensional, 108 accessing elements of, 114–115 bucket, 140–142 closing, 106–108 data structures and, 129–130 hashes vs., 132–133, 144 levels of, 142–144 loops and, 106–112 opening, 106–108 questions about, 108–109, 131 strings and, 128–129 Study Drills on, 108, 131 when to use, 130–131, 143 Asking questions of users decision making and, 102–104 overview of, 42 questions about, 43 Study Drills on, 43 assert commands, 144, 217 Association, 133–136 Asterisk args (*args), 63–65 Automated testing of forms, 229–230 guidelines for, 201 introduction to, 198 questions about, 202 results of, 201 Study Drills on, 202 writing, 198–201 B Backslash (\) characters, 38–40 Before inheritance, 180–182 begin-rescue, 206, 210 bin/ folders, 192–196 Bitbucket.com, 80 Boolean logic overview of, 94–96 questions about, 96 Study Drills on, 96 true/false in, 92 Branches overview of, 116–119 questions about, 119 Study Drills on, 118 Browsers automated testing of forms and, 229–230 de ned, 225 HTML forms and, 226–228 input from, generally, 224 layout templates and, 228–229 questions about, 231 Study Drills on, 230–231 web workings and, 224–226 websites and, 220 Bucket arrays, 140–142 C cat (stream le) command, 285–286 cd (change directory), 260–264 Chef Solo, 242 Child classes, 179–186 chomp, 42–48 Classes Child, 179–186 creating, 148–149 in game engine analysis, 167–169 hierarchies of, 167–168 introduction to, 146–148 modules and, 148–149 nil and, 160–162 in object-oriented programming, generally, 146–151 objects vs., 158 Parent, 179–186 in phrases, 152–153 “Shaw_Index” — 2014/11/8 — 17:18 — page 293 — #3 INDEX style of, 189–190 testing, 168–169 close command, 56 Closing arrays with right bracket (]), 106–108 Command line tools ARGV. See ARGV (argument variable) cat (stream le), 285–286 cd (change directory), 260–264 exit (exit terminal), 289–290 in Linux. See Linux ls (list directory), 264–269 in Mac OS X. See Mac OS X memorizing, 250 mkdir (make directory), 257–259 mv (move le), 281 new-item (create empty le), 276–277 popd (return to saved location), 273–276 pushd (save location, go to new location), 273–276 pwd command, 254–256 references on, 290 rm (remove le), 286–289 rmdir (remove directory), 269–272 setup for, 251 shells, 249 touch (create empty le), 276–277 viewing les with, 283–285 for when lost, 256–257 in Windows. See Windows Comments ## ?? 159–161 in English, 18, 24, 33 in game creation, 190–191 overview of, 18 questions about, 18–19 Study Drills on, 18–19 Connections, de ned, 225 Copying les cp for, 277–281 overview of, 60–61 questions about, 61 Study Drills on, 61 Copy-pasting, 3 Correcting bad code, 88 cp (copy le) command, 277–281 D Data structures, 129–130, 136 Data types, 124 Debugging games, 120–121 Decision making exercises in, 102–103 questions about, 103–104 Study Drills on, 103 def (de ne function), 63, 152 delete, 141 Designing games, 120–121 Details, signi cance of, 2 Dictionaries, 132 Differences, signi cance of, 3 Directories. See Skeleton directories Double equal (==) characters, 25, 92–96 Double quotes ("). See " (double quotes) Drawing problems, 165–166 E Ease of learning, 2–5 Elements of arrays, access to, 114–115 Eloquent Ruby, 242 else conditions elsif as. See elsif making decisions with, 102–104 overview of, 100–101 questions about, 101 Study Drills on, 101 elsif branches and, 116–117 de nition of, 123 introduction to, 101 making decisions with, 102–104 rules for, 120 English comments in, 18, 24, 33 in object-oriented programming, 156 293 “Shaw_Index” — 2014/11/8 — 17:18 — page 294 — #4 294 INDEX Equality operators != (not equal), 91–96 = (single equal). See = (equal) characters == (double equal), 25, 92–96 in Boolean logic, 95–96 Errors debugging games for, 120–121 exceptions as. See Exceptions in if- statements, 100, 120 load, 17 name, 25 ParserError, 213–216 in prompt variables, 51 rake test and, 201–202 reading messages about, 16 spelling, 37 syntax. See Syntax errors tokens, 205 in unpacking variables, 47 in website creation, 221–222 Escape sequences introduction to, 38 overview of, 38–39 questions about, 40 string, 124 Study Drills on, 40 Evaluation of game engines. See Game engine analysis of games, 188–189, 191 object-oriented. See Object-oriented analysis Exceptions numbers and, 206 in sentences, 213 symbols for, 122–123 exit commands, 116–119, 289–290 Explicitly overriding inheritance, 180 Extracting game concepts, 166. See also Game engine analysis F f variable, 70–71 False in Boolean logic, 95–96 format strings and, 34–35 math operators and, 20–21 overview of, 90–92 File.exist?(to_file), 60–61 Files copying, 60–61, 277–281 creating empty, 276–277 functions and, 70–72 moving, 281 opening, 52–58 questions about, 71–72 reading, 52–58 reading backward, 24–26 removing, 286–289 running, 13, 15 streaming, 285–286 Study Drills on, 71 viewing, 283–285 writing, 56–58 First programs on Mac OS X, 12, 14 overview of, 12 questions about, 17 Study Drills on, 16 on Windows, 13, 15 Floating point numbers, 21 for-loop exercises in, 106–108 questions about, 108–109 rules for, 120 Study Drills on, 108 while-loop vs., 112 Format activators, 28, 35 Format strings = characters and, 34–37 overview of, 34 printing, 34 questions about, 35 Study Drills on, 35 Forms automated tests for, 229–230 HTML, 227–231 “Shaw_Index” — 2014/11/8 — 17:18 — page 295 — #5 INDEX layout templates for, 228 overview of, 226–227 Forward-slash ( / ), 38–40 Frequently asked questions on # (pound) characters, 18–19 on advanced user input, 210 on arrays, 108–109, 131 on asking questions of users, 43 on automated testing, 202 on Boolean logic, 96 on branches, 119 on browsers, 231 on comments, 18–19 on copying les, 61 on else conditions, 101 on escape sequences, 40 on rst programs, 17 on format strings, 35 on functions, generally, 65 on functions, values from, 76 on functions and les, 71–72 on functions and variables, 67–68, 87 on has-a phrases, 161–162 on hashes, 144 on if- statements, 99 on inheritance, 186–187 on is-a phrases, 161–162 on for-loop, 108–109 on making decisions, 103–104 on math, 22 on memorizing logic, 92 on names, 25–26 on numbers, 22 on object-oriented analysis, 177 on object-oriented programming, 151, 156 on practicing code, 83, 87 on printing, 33, 37 on prompting and passing, 51 on reading and writing les, 54, 58 on sentences, 217 on skeleton directories, 195–196 on strings, 31 on symbols, 127 295 on text, 31 on variables, 25–26, 47–48 on website creation, 223 on while-loop, 112 Functions branches and, 115–119 checklists for, 64, 70 code and, 62–65 def (de ne function) for, 152 les and, 70–72 in game creation, 189 importing and running, 84–86 names and, 62–65 overview of, 62–64 questions about, 65, 71–72, 76 Study Drills on, 64, 71, 75–76 style of, 189 values and, 74–76 variables and, 62–68, 84–87 G Game engine analysis. See also Games class hierarchies in, 167–168 coding classes in, 168 extracting/researching concepts in, 166 object maps in, 167–168 re ning code in, 169–170 testing classes in, 168–169 top down versus bottom up approach to, 170–176 writing/drawing problems in, 165–166 Game engines analysis of. See Game engine analysis creation of, 238–240 refactoring of, 232–237 session-based, 238–241 Game lexicon exceptions in, 206 introduction to, 204 lexicon types in, 205 numbers in, 206 sentence breaks in, 204–205 writing scanners and, 205 “Shaw_Index” — 2014/11/8 — 17:18 — page 296 — #6 296 INDEX Games analysis of engines for. See Game engine analysis arrays in, 129–131 branches in, 116–119 class style in, 189–190 code style in, 190 comments in, 190–191 debugging, 120–121 designing, 120–121 engines for. See Game engines evaluating, 188–189, 191 function style in, 189 functions in, generally, 116–119 introduction to, 188 lexicon in. See Game lexicon user input in. See Advanced user input on the web. See Web games gedit text editor setup and, 8–9, 11 viewing les in, 283 gem, 218–219 get commands, 141 gets.chomp asking questions of users with, 42–48 opening les with, 52–54 prompting and passing with, 50–51 Github.com, 80 Gitorious.org, 80 Global variables, 68 Google, 10 ”Gothons from Planet Percal #25,” 170–176 Grammar, 213 H Handlers, 222–223, 227 Hard coding, 52 Hard way overview copy-pasting vs., 3 details, signi cance of, 2 differences, signi cance of, 3 ease of learning in, 2 instructional videos, 3 persistence in, 3–4 practice in, 3 reading/writing Ruby in, 2 warnings for programmers in, 4–5 has-a phrases introduction to, 158–159 overview of, 159–161 questions about, 161–162 Study Drills on, 161 Hashes arrays and, 132–133, 142–144 code description for, 140–142 as data structures, 136 exercises in, 133–136 hash_key, 141 introduction to, 132–133 modules and, 136–139, 146–148 questions about, 144 Study Drills on, 143–144 when to use, 143 ”Hello World” project, 219–220. See also Websites HTML (HyperText Markup Language) forms in, 225–231 session-based game engines in, 238–241 websites created in, 222–223 I Idiomatic Ruby, 11 if- statements arrays and, 106 else conditions and, 100–101 exercises in, 98–99 making decisions with, 102–104 questions about, 99 rules for, 120 Study Drills on, 99 Implicit inheritance, 179 Increment by (+=) operators, 71–72, 99 Index.GET, 221–224 Inheritance altering before/after, 180–182 combining types of, 182–183 “Shaw_Index” — 2014/11/8 — 17:18 — page 297 — #7 INDEX composition vs., 183–186 de nition of, 178–179 implicit, 179 introduction to, 178 overriding explicitly, 180 questions about, 186–187 Study Drills on, 186 super() with initialize, 183 when to use, 185–186 initialize, 183 Input methods, 42–47 Instantiating classes, 148–149 Instructional videos, 3 Integer() functions, 206 Intended readers, 4 International programming, 16 Internet browsers and. See Browsers games on. See Web games searching, 10 Irb interpreter, 53–54, 85–86 is-a phrases exercises in, 159–161 introduction to, 158–159 questions about, 161–162 Study Drills on, 161 297 Keywords, 122–123 Linux cat (stream le) in, 285 cd (change directory) in, 260–261 command line tools in, 252–253 cp (copy le) in, 277–278 exit (exit terminal) in, 289 less command in, 284 ls (list directory) in, 265 mkdir (make directory) in, 257 mv (move le) in, 281 popd (return to saved location) in, 273–274 pushd (save location, go to new location) in, 273–274 pwd command in, 255 rm (remove le) in, 286–287 rmdir (remove directory) in, 270 setup on, 8–10 Terminal setup in, 251 touch (create empty le) in, 276–277 Lisp, 5 list, 141 List directory (ls), 264–269 Localhost, 220–225 Loops arrays and, 106–112 for-loop, 106–108, 112, 120 while-loop, 110–112, 120, 169 ls (list directory), 264–269 L M Launchpad.net, 80 Layout templates, 228–229 Learn C the Hard Way, 242 Learn Python the Hard Way, 4, 242 Learn Ruby the Hard Way, 3–4 Learning programming languages, 243–244 Learning Ruby, overview. See Hard way overview Left bracket ([), opening arrays with, 106–108 Lexicon. See Game lexicon Mac OS X cat (stream le) in, 285 cd (change directory) in, 260–261 command line tools in, generally, 252–253 cp (copy le) in, 277–278 exit (exit terminal) in, 289 rst programs on, 12, 14 less command in, 284 ls (list directory) in, 265 mkdir (make directory) in, 257 mv (move le) in, 281 popd (return to saved location) in, 273–274 K “Shaw_Index” — 2014/11/8 — 17:18 — page 298 — #8 298 INDEX Mac OS X (Continued) pushd (save location, go to new location) in, 273–274 pwd command in, 255 rmdir (remove directory) in, 270 running les on, 14 setup on, 6–7 Terminal setup in, 251 touch (create empty le) in, 276–277 Make directory (mkdir), 257–259 Mapping of hashes, 133–136 of objects, 167–168 in refactoring, 232–237 Match and peek, 212–213 Math. See also Numbers algorithms for data structures, 140 overview of, 20–21 questions about, 22 Study Drills on, 21 Mechanize, 242 Memorization of characters, 78 of command line tools, 250 of logic, 90–92 of truth tables, 91–92 of truth terms, 90–91 mkdir (make directory), 257–259 Modules classes and, 148 hashes and, 136–139, 146–148 in object-oriented programming, generally, 146–151 Modulus (%) operators, 22, 35 mv (move le) command, 281 N Names functions and, 62–65 overview of, 24–25 questions about, 25–26 Study Drills on, 25 new (create initializer) command, 140 new-item (create empty le) command, 276–277 nil classes and, 160–162 as data type, 124 hashes and, 132–139 Not (!) expressions, 91–96 Not equal (!=) characters, 91–96 Notepad++ rst programs in, 13 setup and, 7 viewing les in, 283 Numbers. See also Math in game lexicon, 206 overview of, 20–21 questions about, 22 Study Drills on, 21 O Object maps, 167–168 Object scope (@), 125 Object-oriented analysis introduction to, 164–165 questions about, 177 of simple game engines. See Game engine analysis Study Drills on, 176–177 top down versus bottom up approach in, 170–176 Object-oriented programming (OOP) analysis in. See Object-oriented analysis classes in, 148–149 english option in, 156 examples of, 150–151 exercises in, 152 getting things from things in, 150 hashes in, 146–148 introduction to, 148–149 modules in, 146–149 objects in, 148–149 phrase drills for, 152–153 questions about, 151, 156 reading code in, 153–156 “Shaw_Index” — 2014/11/8 — 17:18 — page 299 — #9 INDEX require in, 148–149 Study Drills on, 151 word drills for, 152 Objects @ for, 125 classes vs., 158–161 instantiating, 148–149 maps of, 167–168 in object-oriented programming, generally, 146–151 require and, 148–149 Octothorpe, 18–19 OED (Oxford English Dictionary), 136 OOP (object-oriented programming). See Object-oriented programming (OOP) open(filename), 52–58 Opening arrays with left bracket ([), 106–108 Operators, de ned, 125. See also speci c operators Or (||) expressions, 91–96 Overriding inheritance, 180 Oxford English Dictionary (OED), 136 P Padrino, 242 Parameters, 46–47 Parent classes, 179–186 Parentheses Exponents Multiplication Division Addition Subtraction (PEMDAS), 22 Parsers, 213–216 PEMDAS (Parentheses Exponents Multiplication Division Addition Subtraction), 22 Persistence, 3–4 Phrase drills, 152–153 popd (return to saved location), 273–276 Port 8080, 219–223 Pound (#) characters, See # (pound) characters PowerShell rst programs in, 15–16 references on, 290 running les in, 15 setup and, 6–8 299 Practicing code exercises in, 82–86 importance of, 3 questions about, 83, 87 Study Drills on, 83, 87 Printing format strings, 34–35 practice exercises in, 32–33, 36–37 print for, 42 print_ two for, 62 pwd (print working directory) for, 254–256 questions about, 33, 37 Study Drills on, 33, 37 variables, 28–29 Programmers advice for, 246–247 bad versus good, 86 details, signi cance of, 2 differences, signi cance of, 3 warnings for, 4–5 Programming languages, 243–244 Project skeleton directories. See Skeleton directories Prompting > for, 50–51 for numbers, 44 passing and, 50–51 questions about, 51 Study Drills on, 44, 51 pushd (save location, go to new location), 273–276 puts command comments and, 18–19 format strings and, 34–36 introduction to, 12–13 math symbols and, 20–21 strings and, 30–32 pwd (print working directory), 254–256 Q Questions asked by students. See Frequently asked questions “Shaw_Index” — 2014/11/8 — 17:18 — page 300 — #10 300 INDEX Questions asked of users. See Asking questions of users R rake test automated testing with, 199–202 setting up, 194 syntax errors in, 202 websites and, 230, 232 Rakefile, 193–194, 199–202 .rb suf x, 12 Reading code for les. See Reading les in object-oriented programming, 153–156 resources for, 80–81 in Ruby, generally, 2 symbols in, 126 Reading les backward, 24–26 exercises in, 52–53, 56–57 questions about, 54, 58 read command for, 56 readline command for, 56 Study Drills on, 53, 57–58 Refactoring game engines, 232–237 References, 242, 290 Re ning code, 169–170 Remove directory (rmdir), 269–272 Remove le (rm), 286–289 Requests, de ned, 225–226 require, 148–149 Researching game concepts, 166. See also Game engine analysis Responses, de ned, 226 Return to saved location (popd), 273–276 Right bracket (]), closing arrays with, 106–108 rm (remove le), 286–289 rmdir (remove directory), 269–272 Room class, 232–237 Ruby, introduction to rst programs in, 12–17 idiomatic Ruby, 11 learning, generally. See Hard way overview setting up, 6–11 Ruby on Rails, 242 RubyMotion, 242 Ruby-Processing, 242 Rules for if- statements, 120 for for-loop, 120 for while-loop, 120 Running les, 13, 15 S Save location, go to new location (pushd), 273–276 Scanners, 205 Searching Internet, 10 Sentences breaks in, 204–205 creating, generally, 212 exceptions in, 213 grammar in, 213 match and peek in, 212–213 parsers in, 213–216 questions about, 217 Study Drills on, 217 testing of, 217 Servers, de ned, 226 Session-based game engines, 238–241 Sessions, 237–238 set, 141–142 Setup for command line tools, 251 generally, 6 Internet searches for, 10 on Linux, 8–10 on Mac OS X, 6–7 warnings about, 10–11 on Windows, 7–8 Shells, 249 Sinatra browser interactions with, 220 errors in, 221–222 ”Hello World” project in, 219–220 “Shaw_Index” — 2014/11/8 — 17:18 — page 301 — #11 INDEX installing, 218–219 stopping/reloading, 221 templates in, 222–223 Single equal (=) characters. See = (equal) characters Skeleton directories creating, 192–193 nal structure of, 193–194 introduction to, 192 questions about, 195–196 quiz on, 195 testing setup of, 194 using, 195 Sourceforge.net, 80 Stateless sessions, 237 Stream le (cat) command, 285–286 String escape sequences, 124. See also Escape sequences Strings arrays and, 128–129 escape sequences and, 38 format, 34–35 questions about, 31 Study Drills on, 31 text and, 30–31 variables and, 28–29 Student questions. See Frequently asked questions Study Drills on # characters, 18–19 on accessing elements of arrays, 115 on advanced user input, 209 on arrays, 108, 131 on asking questions of users, 43 on automated testing, 202 on Boolean logic, 96 on branches, 118 on browsers, 230–231 on comments, 18–19 on copying les, 61 on else conditions, 101 on escape sequences, 40 on rst programs, 16 on functions, generally, 64 on functions and les, 71 on functions and values, 75–76 on functions and variables, 67, 87 on has-a phrases, 161 on hashes, 143–144 on if- statements, 99 on inheritance, 186 on is-a phrases, 161 on for-loop, 108 on making decisions, 103 on math, 21 on names, 25 on numbers, 21 on object-oriented analysis, 176–177 on object-oriented programming, 151 on practicing code, 83, 87 on printing, 29, 33, 37 on prompting and passing, 51 on prompting for numbers, 44 on reading les, 53, 57–58 on sentences, 217 on strings, 31 on symbols, 126–127 on text, 31 on variables, 25, 29, 47 on website creation, 223 on while-loop, 112 on writing les, 57–58 Style, 189–190 sudo gem install, 218–221, 229 super() with initialize, 183 super(name), 160–162 Symbols. See also speci c symbols data types, 124 introduction to, 122 keywords, 122–123 operators, 125 questions about, 127 reading code and, 126 string escape sequences, 124 Study Drills on, 126–127 301 “Shaw_Index” — 2014/11/8 — 17:18 — page 302 — #12 302 INDEX Syntax errors branches and, 118 de ned, 16 in if- statements, 100 rake test and, 202 T Templates, 222–223, 228–229 Terminal Boolean logic in, 94 rst programs in, 13–16 running les in, 14 setup and, 6–11 Testing automated. See Automated testing classes, in game engine analysis, 168–169 correcting bad code and, 88 procedures for, 207–209 rake for. See rake test in sentence creation, 217 of skeleton directory setup, 194 user input and, 206–209 Text questions about, 31 strings and, 30–31 Study Drills on, 31 Text editors creating, 56–58 gedit, 8–11, 283 Notepad++ as. See Notepad++ running les on, 12–17 setting up, 6–11 Terminal as. See Terminal TextWrangler as. See TextWrangler TextWrangler rst programs in, 12 setup and, 6, 11 viewing les in, 283 Thor, 242 Top down versus bottom up analysis, 170–176. See also Object-oriented analysis touch (create empty le) command, 276–277 Tracking sessions/users, 237–238 Triple quotes (" " "), 37–38 True format strings and, 34–35 math operators and, 20–21 strings and, 31 truncate command, 56–58 Truth tables, 91–92 Truth terms, 90–91 txt = open(filename), 52–54 Typing, importance of, 2 U Underscore (_) characters, 24 UNIX Bash, 290 Unpacking arguments/variables, 44, 46–48 Upgrades, 240–241 URLs, 220–225 Users asking questions of, 42–43, 102–104 input of. See Advanced user input tracking, 237–238 V Values, 74–76, 121 Variables ARGV. See ARGV (argument variable) f, 70–71 functions and, 62–68, 84–87 global, 68 naming, 24–26 overview of, 24–25 passing to scripts, 46–47 printing, 28–29 questions about, 25–26, 47–48, 67–68 setting to numbers, 44–45 setting to strings, 30–33 strings and, 28–33 Study Drills on, 25, 47, 67 Videos, 3 Viewing les, 283–285 “Shaw_Index” — 2014/11/8 — 17:18 — page 303 — #13 INDEX W 'w,' 56–61 Warnings, 4–5, 10–11 Web games engine creation for, 238–240 introduction to, 232 refactoring engines for, 232–237 sessions in, 237–238 tracking users in, 237–238 upgrades to, 240–241 Websites browsers and. See Browsers creating, generally, 218 error repair in, 221–222 ”Hello World” project, 219–220 questions about, 223 Sinatra for, installing, 218–219 Sinatra for, stopping/reloading, 221 Study Drills on, 223 template creation in, 222–223 The Well-Grounded Rubyist, 242 while true, 116–119 while-loop exercises in, 110–112 in game creation, 169 for-loop vs., 112 questions about, 112 rules for, 120 Study Drills on, 112 Windows cat (stream le) in, 285–286 cd (change directory) in, 261–263 303 command line tools in, 253–254 cp (copy le) in, 278–280 exit (exit terminal) in, 285–286 rst programs on, 13, 15 ls (list directory) in, 265–269 mkdir (make directory) in, 258–259 more command in, 284 mv (move le) in, 281–283 new-item (create empty le) in, 276–277 popd (return to saved location), 274–275 PowerShell setup in, 252 pushd (save location, go to new location), 274–275 pwd command in, 255 rm (remove le) in, 287–288 rmdir (remove directory) in, 271–272 running les on, 15 setup on, 7–8 Word drills, 152 Writing les exercises in, 56–57 questions about, 58 Study Drills on, 57–58 write('stuff') command for, 56 Writing problems, 165–166 Writing scanners, 205 Writing skills, importance of, 2 Z Zen koans, 158 This page intentionally left blank “Shaw_Index” — 2014/11/8 — 17:18 — page 316 — #26 The Addison-Wesley Professional Ruby Series informit.com/ruby Expert reference books, eBooks, and videos from experienced practitioners ISBN-13: 978-0-321-94427-6 ISBN-13: 978-0-321-72133-4 ISBN-13: 978-0-321-83205-4 ISBN-13: 978-0-321-58410-6 ISBN-13: 978-0-13-303999-3 ISBN-13: 978-0-132-80826-2 Look for these titles and more on informit.com/ruby. 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