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  1. 1. Randal K. Michael Mastering Unix Shell Scripting Free & Share & Open
  2. 2. Dear Valued Customer, We realize youre a busy professional with deadlines to hit. Whether your goal is to learn a new technology or solve a critical problem, we want to be there to lend you a hand. Our primary objective is to provide you with the insight and knowledge you need to stay atop the highly competitive and ever- changing technology industry. Wiley Publishing, Inc., offers books on a wide variety of technical categories, including security, data warehousing, software development tools, and networking everything you need to reach your peak. Regardless of your level of expertise, the Wiley family of books has you covered. For Dummies The fun and easy way to learn The Weekend Crash Course The fastest way to learn a new tool or technology Visual For those who prefer to learn a new topic visually The Bible The 100% comprehensive tutorial and reference The Wiley Professional list Practical and reliable resources for IT professionals The book you hold now, Mastering Unix Shell Scripting, is the first book to provide end-to-end scripting solutions that will solve real-world system administration problems for those who have to automate these often complex and repetitive tasks. Starting with a sample task and targeting the most common Unix systems: Solaris, Linux, AIX, and HP-UX with specific command structures, this book will save precious time with hands-on detail. The companion Web site contains all the timesaving scripts from the book. Our commitment to you does not end at the last page of this book. Wed want to open a dialog with you to see what other solutions we can provide. Please be sure to visit us at to review our complete title list and explore the other resources we offer. If you have a comment, suggestion, or any other inquiry, please locate the contact us link at Thank you for your support and we look forward to hearing from you and serving your needs again in the future. Sincerely, Richard K. Swadley Vice President & Executive Group Publisher Wiley Technology Publishing WILEYadvantage The Free & Share & Open
  3. 3. Mastering Unix Shell Scripting Free & Share & Open
  4. 4. Randal K. Michael Mastering Unix Shell Scripting Free & Share & Open
  5. 5. Publisher: Robert Ipsen Executive Editor: Carol Long Developmental Editor: Scott Amerman Managing Editor: Angela Smith Text Design & Composition: Wiley Composition Services This book is printed on acid-free paper. Copyright 2003 by Randal K. Michael. All rights reserved. Published by Wiley Publishing, Inc., Indianapolis, Indiana Published simultaneously in Canada No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rose- wood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4470. Requests to the Pub- lisher for permission should be addressed to the Legal Department, Wiley Publishing, Inc., 10475 Crosspoint Blvd., Indianapolis, IN 46256, (317) 572-3447, fax (317) 572-4447, E-mail: PERMCOORDINATOR@WILEY.COM. Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, inci- dental, consequential, or other damages. For general information on our other products and services please contact our Customer Care Department within the United States at (800) 762-2974, outside the United States at (317) 572-3993 or fax (317) 572-4002. Trademarks: Wiley, the Wiley Publishing logo and related trade dress are trademarks or registered trademarks of Wiley Publishing, Inc., in the United States and other countries, and may not be used without written permission. All other trademarks are the property of their respective owners. Wiley Publishing, Inc., is not associated with any product or ven- dor mentioned in this book. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. Library of Congress Cataloging-in-Publication Data: ISBN: 0-471-21821-9 Printed in the United States of America 10 9 8 7 6 5 4 3 2 1
  6. 6. This book is dedicated to My Wife Robin, and the girls, Andrea and Ana Free & Share & Open
  7. 7. The information that I gathered together in this book is the result of working with some of the most talented UNIX professionals on the topic. I have enjoyed every minute of my association with these UNIX gurus and it has been my pleasure to have the opportunity to gain so much knowledge from the pros. I want to thank every one of these experts for asking and answering questions over the last fifteen years. If my brother, Jim, had not kept telling me, you should write a book, after querying me for UNIX details on almost a weekly basis, I doubt this book would have ever been writ- ten. So, thanks Jim! I especially want to thank Jack Renfro at Daimler/Chrysler Corporation for giving me my first shell scripting project so long ago. I had to start with the man pages, but that is how I learned to dig deep to get an answer. Since then I have been on a mission to automate, through shell scripting, everything on every system that I come in contact with. I certainly value the years that I was able to work with Jack. I must also thank the talented people at Wiley Publishing. Margaret Eldridge started me on this project by letting me do my own thing, and Carol Long kept me going. Scott Amerman kept me on schedule, and Angela Smith did the edits that make my writing flow with ease. It has been a valuable experience for me to work with such a fine group of professionals at Wiley. I also want to thank Carole McClendon at Waterside Produc- tions for all of the support on this project. Carole is the best Agent that anyone could ever ask for. She is a true professional with the highest ethics. Of course my family had a lot to do with my success on this and every project. I want to thank Mom, Gene, Jim, Marcia, Rusty, Mallory, and Anica. I want to thank my Wife Robin for her understanding and support. The girls, Andrea and Ana, always keep a smile on my face, and Steve is always on my mind. I could not have written this book without the support of all of these people and the many others that remain unnamed. It has been an honor! Acknowledgments vii Free & Share & Open
  8. 8. Acknowledgments vii Introduction xix Chapter 1 Scripting Quick Start and Review 1 Case Sensitivity 1 Unix Special Characters 2 Shells 2 Shell Scripts 2 Functions 2 A Function Has the Form 3 Running a Shell Script 3 Declare the Shell in the Shell Script 3 Comments and Style in Shell Scripts 4 Control Structures 6 Using break, continue, exit, and return 9 Here Document 9 Syntax for a Here Document 9 Shell Script Commands 10 Symbol Commands 13 Variables 13 Command-Line Arguments 13 Shift Command 14 Special Parameters $* and $@ 15 Special Parameter Definitions 15 Double Quotes , Forward Tics , and Back Tics ` 16 Math in a Shell Script 17 Operators 17 Built-in Mathematical Functions 18 Contents ix Free & Share & Open
  9. 9. File Permissions, suid and sgid Programs 18 chmod Command Syntax for Each Purpose 19 Running Commands on a Remote Host 20 Setting Traps 21 User Information Commands 22 who Command 22 w Command 22 last Command 22 ps Command 23 Communicating with Users 23 Uppercase or Lowercase Text for Easy Testing 24 Check the Return Code 25 Time-Based Script Execution 27 cron tables 27 Cron Table Entry Syntax 27 Wildcards 28 at Command 28 Output Control 28 Silent Running 28 Using getopts to Parse Command-Line Arguments 29 Making a Co-Process with Background Function 30 Catching a Delayed Command Output 32 Fastest Ways to Process a File Line -by Line 33 Mail Notification Techniques 34 Using the mail and mailx Commands 34 Using the sendmail Command to Send Outbound Mail 34 Creating a Progress Indicator 35 A Series of Dots 35 A Rotating Line 35 Creating a Psuedo-Random Number 36 Checking for Stale Disk Partitions in AIX 37 Automated Host Pinging 37 Highlighting Specific Text in a File 38 Keeping the Printers Printing 38 AIX Classic Printer Subsystem 38 System V Printing 39 Automated FTP File Transfer 39 Capturing a List of Files Larger than $MEG 39 Capturing a Users Keystrokes 40 Using the bc Utility for Floating-Point Math 40 Number Base Conversions 41 Using the typeset Command 41 Using the printf Command 41 Create a Menu with the select Command 42 Sending Pop-Up Messages to Windows 43 Removing Repeated Lines in a File 43 Removing Blank Lines from a File 44 x Contents
  10. 10. Testing for a Null Variable 44 Directly Access the Value of the Last Positional Parameter, $# 45 Remove the Columns Heading in a Command Output 45 Arrays 46 Loading an Array 46 Testing a String 47 Summary 51 Chapter 2 Twelve Ways to Process a File Line by Line 53 Command Syntax 53 Using File Descriptors 54 Creating a Large File to


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