Advanced Bash−Scripting Guide

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Chapter 36. Endnotes 36.1. Author's Note How did I come to write a Bash scripting book? It's a strange tale. It seems that a couple of years back, I needed to learn shell scripting −− and what better way to do that than to read a good book on the subject? I was looking to buy a tutorial and reference covering all aspects of the subject. I was looking for a book that would take difficult concepts, turn them inside out, and explain them in excruciating detail with well−commented examples. [67] In fact, I was looking for this very book, or something much like it. Unfortunately, it didn't exist, and if I wanted it, I'd have to write it. And so, here we are, folks. This reminds me of the apocryphal story about the mad professor. Crazy as a loon, the fellow was. At the sight of a book, any book −− at the library, at a bookstore, anywhere −− he would become totally obsessed with the idea that he could have written it, should have written it, and done a better job of it to boot. He would thereupon rush home and proceed to do just that, write a book with the very same title. When he died some years later, he allegedly had several thousand books to his credit, probably putting even Asimov to shame. The books might not have been any good, who knows, but does that really matter? Here's a fellow who lived his dream, even if he was obsessed by it, driven by it, and I can't help admiring the old coot... 36.2. About the Author Who is this guy anyhow? The author claims no credentials or special qualifications, other than a compulsion to write. [68] This book is somewhat of a departure from his other major work, HOW−2 Meet Women: The Shy Man's Guide to Relationships. He has also written the Software−Building HOWTO. A Linux user since 1995 (Slackware 2.2, kernel 1.2.1), the author has emitted a few software truffles, including the cruft one−time pad encryption utility, the mcalc mortgage calculator, the judge Scrabble® adjudicator, and the yawl word gaming list package. He got his start in programming using FORTRAN IV on a CDC 3800, but is not the least bit nostalgic for those days. Living in a secluded desert community with wife and dog, he cherishes human frailty. 36.3. Tools Used to Produce This Book 36.3.1. Hardware A used IBM Thinkpad, model 760XL laptop (P166, 104 meg RAM) running Red Hat 7.1/7.3. Sure, it's slow and has a funky keyboard, but it beats the heck out of a No. 2 pencil and a Big Chief tablet. 36.3.2. Software and Printware i. Bram Moolenaar's powerful SGML−aware vim text editor. ii. OpenJade, a DSSSL rendering engine for converting SGML documents into other formats. iii. Norman Walsh's DSSSL stylesheets. iv. DocBook, The Definitive Guide, by Norman Walsh and Leonard Muellner (O'Reilly, ISBN Chapter 36. Endnotes 360
1−56592−580−7). This is the standard reference for anyone attempting to write a document in Docbook SGML format. 36.4. Credits Community participation made this project possible. The author gratefully acknowledges that writing this book would have been an impossible task without help and feedback from all you people out there. Philippe Martin translated this document into DocBook/SGML. While not on the job at a small French company as a software developer, he enjoys working on GNU/Linux documentation and software, reading literature, playing music, and for his peace of mind making merry with friends. You may run across him somewhere in France or in the Basque Country, or email him at feloy@free.fr. Philippe Martin also pointed out that positional parameters past $9 are possible using {bracket} notation, see Example 4−5. Stephane Chazelas sent a long list of corrections, additions, and example scripts. More than a contributor, he has, in effect, taken on the role of editor for this document. Merci beaucoup! I would like to especially thank Patrick Callahan, Mike Novak, and Pal Domokos for catching bugs, pointing out ambiguities, and for suggesting clarifications and changes. Their lively discussion of shell scripting and general documentation issues inspired me to try to make this document more readable. I'm grateful to Jim Van Zandt for pointing out errors and omissions in version 0.2 of this document. He also contributed an instructive example script. Many thanks to Jordi Sanfeliu for giving permission to use his fine tree script (Example A−18). Likewise, thanks to Michel Charpentier for permission to use his dc factoring script (Example 12−37). Kudos to Noah Friedman for permission to use his string function script (Example A−19). Emmanuel Rouat suggested corrections and additions on command substitution and aliases. He also contributed a very nice sample .bashrc file (Appendix G). Heiner Steven kindly gave permission to use his base conversion script, Example 12−33. He also made a number of corrections and many helpful suggestions. Special thanks. Rick Boivie contributed the delightfully recursive pb.sh script (Example 34−7) and suggested performance improvements for the monthlypmt.sh script (Example 12−32). Florian Wisser enlightened me on some of the fine points of testing strings (see Example 7−6), and on other matters. Oleg Philon sent suggestions concerning cut and pidof. Advanced Bash−Scripting Guide Michael Zick extended the empty array example to demonstrate some surprising array properties. He also provided other examples of this. Marc−Jano Knopp sent corrections on DOS batch files. Chapter 36. Endnotes 361
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Chapter 1. Why Shell Programming? A
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Chapter 2. Starting Off With a Sha
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Chapter 3. Special Characters Speci
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# Sometimes, though, you get: # 11
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The "−" can be used to pipe stdou
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change the behavior of the terminal
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Chapter 4. Introduction to Variable
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The shift command reassigns the pos
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Example 5−1. Echoing Weird Variab
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(cd /source/directory && tar cf −
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true # the "true" builtin. echo "ex
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if [[ −e $file ]] then echo "Pass
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7.3. Comparison operators (binary)
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Example 7−5. arithmetic and strin
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Chapter 8. Operations and Related T
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Part 3. Beyond the Basics Table of
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$EDITOR the default editor invoked
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Example 9−2. Timed Input Advanced
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echo 'IFS=":", using "$@"' c=0 for
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echo '${var1#$pattern1} =' "${var1#
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t=${path_name%/*.*} # Same effect a
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Chapter 10. Loops and Branches Oper
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As is the case with for/in loops, p
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This construct tests for a conditio
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# Accept upper or lowercase input.
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# May need to also press ENTER if a
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cat, tac # Burn the CDR. cdrecord
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Advanced Bash−Scripting Guide 12.
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exit $E_CHANGED_MIND ;; *) echo "De
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The multiplication operator must be
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echo Number of digits at the beginn
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Outputs very verbose timing statist
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This line occurs three times. This
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# List all the users in /etc/passwd
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The −d option deletes a range of
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# Delete CR and write to new file.
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mailto Similar to the mail command,
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[ ${NETWORKING} = "no" ] && exit 0
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chroot Advanced Bash−Scripting Gu
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Chapter 15. Arithmetic Expansion Ar
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# Saves stdin. Advanced Bash−Scri
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Chapter 17. Here Documents A here d
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Example 17−11. A self−documenti
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Part 4. Advanced Topics At this poi
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"Sed & Awk", by Dougherty and Robbi
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# Range: 0 − 200 # It's crude, bu
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# grep PATTERN /etc/passwd | awk
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Chapter 25. List Constructs The "an
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# AND LIST executes on true, OR LIS
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fi let "t += $i " Primes[t]=$NON_PR
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Appendix D. A Detailed Introduction
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Appendix E. Localization Localizati
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Appendix F. History Commands The Ba
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Appendix H. Converting DOS Batch Fi
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Appendix I. Exercises I.1. Analyzin
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Lottery Numbers One type of lottery
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[33] This is actually a script adap
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# Thanks to Stephane Chazelas for p
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