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(2) beginning linux-programming-third-edition.9780764544972.24103(1)

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  • 1. Beginning Linux®Programming Third Edition Neil Matthew Richard Stones
  • 2. Beginning Linux®Programming Third Edition Neil Matthew Richard Stones
  • 3. Beginning Linux® ProgrammingThird EditionPublished byWiley Publishing, Inc.10475 Crosspoint BoulevardIndianapolis, IN 46256Copyright © 2004 by Wiley Publishing, Inc. All rights reserved.Published simultaneously in CanadaNo part of this publication may be reproduced, stored in a retrieval system, or transmitted in any formor by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except aspermitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the priorwritten permission of the Publisher, or authorization through payment of the appropriate per-copy feeto the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax(978) 646-8600. Requests to the Publisher 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 AUTHORHAVE USED THEIR BEST EFFORTS IN PREPARING THIS BOOK, THEY MAKE NO REPRESENTA-TIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY OR COMPLETENESS OF THECONTENTS OF THIS BOOK AND SPECIFICALLY DISCLAIM ANY IMPLIED WARRANTIES OFMERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. NO WARRANTY MAY BECREATED OR EXTENDED BY SALES REPRESENTATIVES OR WRITTEN SALES MATERIALS.THE ADVICE AND STRATEGIES CONTAINED HEREIN MAY NOT BE SUITABLE FOR YOUR SIT-UATION. YOU SHOULD CONSULT WITH A PROFESSIONAL WHERE APPROPRIATE. NEITHERTHE PUBLISHER NOR AUTHOR SHALL BE LIABLE FOR ANY LOSS OF PROFIT OR ANY OTHERCOMMERCIAL DAMAGES, INCLUDING BUT NOT LIMITED TO SPECIAL, INCIDENTAL, CON-SEQUENTIAL, OR OTHER DAMAGES.For general information on our other products and services please contact our Customer Care Depart-ment within the United States at (800) 762-2974, outside the United States at (317) 572-3993 or fax (317)572-4002.Trademarks: Wiley, Wrox, the Wrox logo, and related trade dress are trademarks or registered trade-marks of John Wiley & Sons, Inc. and/or its affiliates in the United States and other countries, and maynot be used without written permission. Linux is a trademark of Linus Torvalds. All other trademarksare the property of their respective owners. Wiley Publishing, Inc., is not associated with any product orvendor mentioned in this book.Wiley also publishes its books in a variety of electronic formats. Some content that appears in printmay not be available in electronic books.Library of Congress Control Number: 2003115911ISBN: 0-7645-4497-7Printed in the United States of America10 9 8 7 6 5 4 3 2 13B/RX/RS/QT/IN
  • 4. About Neil Matthew Neil Matthew has been interested in and has programmed computers since 1974. A mathematics graduate from the University of Nottingham, Neil is just plain keen on programming languages and likes to explore new ways of solving computing problems. He’s written systems to program in BCPL, FP (Functional Programming), Lisp, Prolog, and a structured BASIC. He even wrote a 6502 microprocessor emulator to run BBC microcomputer programs on UNIX systems. In terms of UNIX experience, Neil has used almost every flavor since the late 1970s, including BSD UNIX, AT&T System V, Sun Solaris, IBM AIX, many others, and of course Linux. Neil can claim to have been using Linux since August 1993 when he acquired a floppy disk distribution of Soft Landing (SLS) from Canada, with kernel version 0.99.11. He’s used Linux-based computers for hacking C, C++, Icon, Prolog, Tcl, and Java at home and at work. Most of Neil’s “home” projects were originally developed using SCO UNIX, but they’ve all ported to Linux with little or no trouble. He says Linux is much easier because it supports quite a lot of features from other systems, so that both BSD- and System V–targeted programs will generally compile with little or no change. As the head of software and principal engineer at Camtec Electronics in the 1980s, Neil programmed in C and C++ for real-time embedded systems. Since then he’s worked on software development tech- niques and quality assurance. After a spell as a consultant with Scientific Generics he is currently work- ing as a systems architect with Celesio AG. Neil is married to Christine and has two children, Alexandra and Adrian. He lives in a converted barn in Northamptonshire, England. His interests include solving puzzles by computer, music, science fiction, squash, mountain biking, and not doing it yourself.About Rick Stones Rick started programming at school, more years ago than he cares to remember, on a 6502-powered BBC micro, which with the help of a few spare parts continued to function for the next 15 years. He graduated from Nottingham University with a degree in Electronic Engineering, but decided software was more fun. Over the years he has worked for a variety of companies, from the very small with just a dozen employ- ees, to the very large, including the IT services giant EDS. Along the way he has worked on a range of projects, from real-time communications to accounting systems, very large help desk systems, and more recently as the technical authority on a large EPoS and retail central systems program. A bit of a programming linguist, he has programmed in various assemblers, a rather neat proprietary telecommunications language called SL-1, some FORTRAN, Pascal, Perl, SQL, and smidgeons of Python and C++, as well as C. (Under duress he even admits that he was once reasonably proficient in Visual Basic, but tries not to advertise this aberration.) Rick lives in a village in Leicestershire, England, with his wife Ann, children Jennifer and Andrew, and two cats. Outside work his main interest is classical music, especially early religious music, and he even does his best to find time for some piano practice. He is currently trying to learn to speak German.
  • 5. CreditsAuthors Vice President and Executive PublisherNeil Matthew Bob IpsenRichard Stones Vice President and PublisherExecutive Editor Joseph B. WikertDebra Williams Cauley Executive Editorial DirectorDevelopment Editor Mary BednarekJames H. Russell Project CoordinatorsProduction Editor Regina SnyderPamela Hanley April FarlingTechnical Editors Graphics and Production SpecialistsArthur Griffith Steved AranyTobias DiPasquale Beth Brooks Carrie FosterCopy Editor Lauren GoddardPublication Services Kristin McMullan Janet SeibSenior Production ManagerFred Bernardi Quality Control Technicians Laura AlbertEditorial Manager Andy HollandbeckMary Beth Wakefield Rob SpringerVice President & Executive Group Publisher Proofreading and IndexingRichard Swadley TECHBOOKS Production Services
  • 6. Contents Foreword by Alan Cox xxxi Introduction xxxiiiChapter 1: Getting Started 1 An Introduction to UNIX, Linux, and GNU 1 What Is UNIX? 1 A Brief History of UNIX 2 UNIX Philosophy 2 What Is Linux? 3 The GNU Project and the Free Software Foundation 3 Linux Distributions 4 Programming Linux 5 Linux Programs 5 The C Compiler 6 Try It Out—Our First Linux C Program 7 Development System Roadmap 8 Applications 8 Header Files 8 Library Files 9 Static Libraries 10 Try It Out—Static Libraries 10 Shared Libraries 12 Getting Help 13 Try It Out—Manual Pages and info 14 Summary 15Chapter 2: Shell Programming 17 Why Program with a Shell? 18 A Bit of Philosophy 18 What Is a Shell? 19 Pipes and Redirection 21 Redirecting Output 21 Redirecting Input 22 Pipes 23
  • 7. Contents The Shell as a Programming Language 23 Interactive Programs 23 Creating a Script 25 Making a Script Executable 26 Shell Syntax 27 Variables 28 Quoting 28 Try It Out—Variables 29 Environment Variables 29 Parameter Variables 30 Try It Out—Parameter and Environment Variables 31 Conditions 32 The test, or [, Command 32 Control Structures 35 if 35 Try It Out—Using the if Command 35 elif 36 Try It Out—Doing Further Checks with an elif 36 A Problem with Variables 36 for 37 Try It Out—for Loop with Fixed Strings 38 Try It Out—for Loop with Wildcard Expansion 38 while 39 Try It Out—Here We Go Again, Again 40 until 41 case 41 Try It Out—Case I: User Input 42 Try It Out—Case II: Putting Patterns Together 42 Try It Out—Case IIl: Executing Multiple Statements 43 Lists 44 Try It Out—AND Lists 45 Try It Out—OR Lists 46 Statement Blocks 47 Functions 47 Try It Out—A Simple Function 47 Try It Out—Returning a Value 49 Commands 50 break 50 The : Command 51viii
  • 8. Contents continue 51 The . Command 52 Try It Out—The Dot Command 53 echo 53 eval 54 exec 54 exit n 55 export 55 Try It Out—Exporting Variables 56 expr 56 printf 57 return 58 set 58 shift 59 trap 60 Try It Out—Trapping Signals 60 unset 62 Two More Useful Commands and Regular Expressions 62 Try It Out—find with Tests 64 Try It Out—Basic grep Usage 66 Try It Out—Regular Expressions 68 Command Execution 69 Arithmetic Expansion 70 Parameter Expansion 70 Try It Out—Parameter Processing 72 Here Documents 73 Try It Out—Using Here Documents 73 Try It Out—Another Use for a Here Document 74 Debugging Scripts 75Going Graphical—The Dialog Utility 76 Try It Out—Using the dialog Utility 78 Try It Out 79Putting It All Together 80 Requirements 81 Design 81 Try It Out—A CD Application 83 Notes on the Application 90Summary 90 ix
  • 9. ContentsChapter 3: Working with Files 91 Linux File Structure 92 Directories 92 Files and Devices 93 /dev/console 93 /dev/tty 93 /dev/null 94 System Calls and Device Drivers 94 Library Functions 95 Low-Level File Access 96 write 96 read 97 open 98 Initial Permissions 100 umask 100 close 101 ioctl 102 Try It Out—A File Copy Program 102 Other System Calls for Managing Files 104 lseek 104 fstat, stat, and lstat 104 dup and dup2 106 The Standard I/O Library 107 fopen 108 fread 108 fwrite 109 fclose 109 fflush 109 fseek 110 fgetc, getc, and getchar 110 fputc, putc, and putchar 110 fgets and gets 111 Formatted Input and Output 111 printf, fprintf, and sprintf 112 scanf, fscanf, and sscanf 114 Other Stream Functions 116 Try It Out—Another File Copy Program 116 Stream Errors 117 Streams and File Descriptors 118 File and Directory Maintenance 118 chmod 118 chown 119x
  • 10. Contents unlink, link, and symlink 119 mkdir and rmdir 119 chdir and getcwd 120 Scanning Directories 120 opendir 121 readdir 121 telldir 122 seekdir 122 closedir 122 Try It Out—A Directory-Scanning Program 122 Errors 125 strerror 125 perror 126 The /proc File System 126 Advanced Topics: fcntl and mmap 130 fcntl 130 mmap 131 Try It Out—Using mmap 132 Summary 134Chapter 4: The Linux Environment 135 Program Arguments 135 Try It Out—Program Arguments 137 getopt 138 Try It Out—getopt 139 getopt_long 140 Environment Variables 142 Try It Out—getenv and putenv 143 Use of Environment Variables 144 The environ Variable 145 Try It Out—environ 145 Time and Date 146 Try It Out—time 146 Try It Out—gmtime 148 Try It Out—ctime 150 Try It Out—strftime and strptime 152 Temporary Files 153 Try It Out—tmpnam and tmpfile 154 User Information 155 Try It Out—User Information 156 Host Information 158 Try It Out—Host Information 159 xi
  • 11.