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Shell Scripting Recipes
A Problem-Solution Approach
CHRIS F. A. JOHNSON
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Shell Scripting Recipes: A Problem-Solution Approach
Copyright © 2005 by Chris F. A. Johnson
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Contents at a Glance
About the Author . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv
About the Technical Reviewer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi
CHAPTER 1
The POSIX Shell and Command-Line Utilities . . . . . . . . . . . . . . . . . . . . 1
CHAPTER 2
Playing with Files: Viewing, Manipulating,
and Editing Text Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
CHAPTER 3
String Briefs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
CHAPTER 4
What’s in a Word? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
CHAPTER 5
Scripting by Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
CHAPTER 6
Loose Names Sink Scripts: Bringing Sanity to Filenames . . . . . . . 137
CHAPTER 7
Treading a Righteous PATH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
CHAPTER 8
The Dating Game . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
CHAPTER 9
Good Housekeeping: Monitoring and Tidying Up
File Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
CHAPTER 10
POP Goes the E-Mail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
CHAPTER 11
PostScript: More Than an Afterthought . . . . . . . . . . . . . . . . . . . . . . . . 229
CHAPTER 12
Screenplay: The screen–funcs Library . . . . . . . . . . . . . . . . . . . . . . . . . 251
CHAPTER 13
Backing Up the Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
CHAPTER 14
Aging, Archiving, and Deleting Files . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
CHAPTER 15
Covering All Your Databases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
CHAPTER 16
Home on the Web . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
CHAPTER 17
Taking Care of Business . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345
CHAPTER 18
Random Acts of Scripting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
CHAPTER 19
A Smorgasbord of Scripts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
CHAPTER 20
Script Development Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
APPENDIX
Internet Scripting Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407
INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411
iii
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Contents
About the Author . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv
About the Technical Reviewer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi
CHAPTER 1 The POSIX Shell and Command-Line Utilities . . . . . . . . . . . . . . 1
Shell Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
echo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
printf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
shift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
getopts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
eval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
local . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Parameters and Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Positional Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Special Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
standard-vars—A Collection of Useful Variables . . . . . . . . . . . . . . . . . 9
Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Pathname Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Regular Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Parameter Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
The Bourne Shell Expansions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
POSIX Parameter Expansions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Shell-Specific Expansions, bash2, and ksh93 . . . . . . . . . . . . . . . . . . 15
Shell Arithmetic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Aliases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Sourcing a File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
v
■
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vi
■ CONTENTS
Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Functions Are Fast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Command Substitution Is Slow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Using the Functions in This Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
standard-funcs: A Collection of Useful Commands . . . . . . . . . . . . . . . . . . . 19
1.1 get_key—Get a Single Keystroke from the User . . . . . . . . . . . . 19
1.2 getline—Prompt User to Enter a Line . . . . . . . . . . . . . . . . . . . . . . 20
1.3 press_any_key—Prompt for a Single Keypress . . . . . . . . . . . . . 21
1.4 menu1—Print a Menu and Execute a Selected
Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
1.5 arg—Prompt for Required Argument If None Supplied . . . . . . . 23
1.6 die—Print Error Message and Exit with Error Status . . . . . . . . . 24
1.7 show_date—Display Date in D[D] MMM YYYY Format . . . . . . . 25
1.8 date_vars—Set Date and Time Variables . . . . . . . . . . . . . . . . . . . 26
1.9 is_num—Is This a Positive Integer? . . . . . . . . . . . . . . . . . . . . . . . 28
1.10 abbrev_num—Abbreviate Large Numbers . . . . . . . . . . . . . . . . 29
1.11 commas—Add Thousands Separators to a Number . . . . . . . . 30
1.12 pr1—Print Arguments, One to a Line . . . . . . . . . . . . . . . . . . . . . 32
1.13 checkdirs—Check for Directories; Create If Necessary . . . . . 33
1.14 checkfiles—Check That a Directory Contains Certain
Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
1.15 zpad—Pad a Number with Leading Zeroes . . . . . . . . . . . . . . . . 34
1.16 cleanup—Remove Temporary Files and Reset Terminal
on Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
The Unix Utilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
cat: Concatenate Files to the Standard Output . . . . . . . . . . . . . . . . . . 36
sed: A Text Stream Editor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
awk: Pattern Scanning and Processing Language . . . . . . . . . . . . . . . 37
grep: Print Lines Matching a Regular Expression . . . . . . . . . . . . . . . . 38
date: Show or Set the System Date . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
tr: A Character Translation Utility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
wc: Count Characters, Words, and Lines in a File . . . . . . . . . . . . . . . 38
file: Determine the File Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
ls: Sort and Provide Details About Files . . . . . . . . . . . . . . . . . . . . . . . . 39
uniq: Remove Consecutive Duplicate Lines . . . . . . . . . . . . . . . . . . . . . 39
sudo: Execute Commands as the Superuser . . . . . . . . . . . . . . . . . . . 40
split: Divide a File into Equal-Sized Pieces . . . . . . . . . . . . . . . . . . . . . 40
which: Show the Full Path to a Command . . . . . . . . . . . . . . . . . . . . . . 40
gs, gv: Render, Convert, or View PostScript and PDF Files . . . . . . . . 40
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
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