Expert Shell Scripting
■■■
Ron Peters
Expert Shell Scripting
Copyright © 2009 by Ron Peters
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iv
Contents at a Glance
About the Author . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv
About the Technical Reviewer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xvii
Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi
PART 1 ■ ■ ■ Basic Scripting Techniques
■CHAPTER 1 Shell Script Debugging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
■CHAPTER 2 Standard Function Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
■CHAPTER 3 Date and Time Manipulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
■CHAPTER 4 Comparisons and Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
■CHAPTER 5 Accepting Command-Line Options, Switches,
and Parameters
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
■CHAPTER 6 Testing Variables and Assigning Defaults . . . . . . . . . . . . . . . . . . . . . . 37
■CHAPTER 7 Indirect Reference Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
■CHAPTER 8 Shell Process Tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
■CHAPTER 9 Data Redirection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
■CHAPTER 10 Piping Input to read . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
PART 2 ■ ■ ■ System Interaction and Advanced
Techniques
■CHAPTER 11 Math from the Shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
■CHAPTER 12 cron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
■CHAPTER 13 Self-Linked Scripts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
■CHAPTER 14 Throttling Parallel Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
■CHAPTER 15 Command-Line Editing and History. . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
■CHAPTER 16 Scripting from the Command Line. . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
■CHAPTER 17 Automating User Input with expect. . . . . . . . . . . . . . . . . . . . . . . . . . . 107
■CHAPTER 18 User Input Timeout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
■CHAPTER 19 Instant Keyboard Response. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
■CHAPTER 20 Directory Copying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
■CHAPTER 21 A Brief Tour of the X Display Environment . . . . . . . . . . . . . . . . . . . . 131
■CHAPTER 22 X Navigation Window. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
■CHAPTER 23 Command-Line E-mail Attachments . . . . . . . . . . . . . . . . . . . . . . . . . . 151
■CHAPTER 24 Text-Processing One-Liners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
■CHAPTER 25 Editing Files in Place . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
■CHAPTER 26 Evaluating Variables in a Flat File . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
■CHAPTER 27 Read Piped Input. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
■CHAPTER 28 Free-Format Output Using cat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
■CHAPTER 29 Automating Interactive Processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
PART 3 ■ ■ ■ Useful Scripts
■CHAPTER 30 Automating E-Mail with procmail . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
■CHAPTER 31 Process-Management Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
■CHAPTER 32 Managing File Counts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
■CHAPTER 33 Processes Running from inittab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
■CHAPTER 34 Automatic RCS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
■CHAPTER 35 Colorful /proc Reporting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
■CHAPTER 36 Password-Aging Notification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
■CHAPTER 37 A Pseudo–shadow File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
■CHAPTER 38 Linux Gold-System Build . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
■CHAPTER 39 System Snapshots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
■CHAPTER 40 Removing Large Files and Log Rolling . . . . . . . . . . . . . . . . . . . . . . . . 261
■CHAPTER 41 Core Finder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
■CHAPTER 42 Network Adapter Failover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
■APPENDIX A Test Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
■APPENDIX B Special Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
■APPENDIX C Other Shell-Scripting Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
■INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
