Linux - Advanced Bash Shell Scripting Guide.pdf - system LINUX - rav022

Advanced Bash-Scripting Guide

An in-depth exploration of the gentle art of

shell scripting

Mendel Cooper

Brindle-Phlogiston Associates

thegrendel@theriver.com

16 June 2002

Revision History

Revision 0.1

14 June 2000

Revised by: mc

Initial release.

Revision 0.2 30 October 2000 Revised by: mc

Bugs fixed, plus much additional material and more example scripts.

Revision 0.3

12 February 2001

Revised by: mc

Another major update.

Revision 0.4 08 July 2001 Revised by: mc

More bugfixes, much more material, more scripts - a complete revision and expansion of

the book.

Revision 0.5 03 September 2001 Revised by: mc

Major update. Bugfixes, material added, chapters and sections reorganized.

Revision 1.0

14 October 2001

Revised by: mc

Bugfixes, reorganization, material added. Stable release.

Revision 1.1

06 January 2002

Revised by: mc

Bugfixes, material and scripts added.

Revision 1.2

31 March 2002

Revised by: mc

Bugfixes, material and scripts added.

Revision 1.3

02 June 2002

Revised by: mc

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Advanced Bash-Scripting Guide

'TANGERINE' release: A few bugfixes, much more material and scripts added.

Revision 1.4 16 June 2002 Revised by: mc

'MANGO' release: Quite a number of typos fixed, more material and scripts added.

This tutorial assumes no previous knowledge of scripting or programming, but progresses

rapidly toward an intermediate/advanced level of instruction ...all the while sneaking in little

snippets of UNIX wisdom and lore . It serves as a textbook, a manual for self-study, and a

reference and source of knowledge on shell scripting techniques. The exercises and heavily-

commented examples invite active reader participation, under the premise that the only

way to really learn scripting is to write scripts .

The latest update of this document, as an archived, bzip2-ed "tarball" including both the

SGML source and rendered HTML, may be downloaded from the author's home site . See

the change log for a revision history.

Dedication

For Anita, the source of all the magic

Table of Contents

Part 1. Introduction

1. Why Shell Programming?

2. Starting Off With a Sha-Bang

Part 2. Basics

3. Exit and Exit Status

4. Special Characters

5. Introduction to Variables and Parameters

6. Quoting

7. Tests

8. Operations and Related Topics

Part 3. Beyond the Basics

9. Variables Revisited

10. Loops and Branches

11. Internal Commands and Builtins

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Advanced Bash-Scripting Guide

12. External Filters, Programs and Commands

13. System and Administrative Commands

14. Command Substitution

15. Arithmetic Expansion

16. I/O Redirection

17. Here Documents

18. Recess Time

Part 4. Advanced Topics

19. Regular Expressions

20. Subshells

21. Restricted Shells

22. Process Substitution

23. Functions

24. Aliases

25. List Constructs

26. Arrays

27. Files

28. /dev and /proc

29. Of Zeros and Nulls

30. Debugging

31. Options

32. Gotchas

33. Scripting With Style

34. Miscellany

35. Bash, version 2

36. Endnotes

36.1. Author's Note

36.2. About the Author

36.3. Tools Used to Produce This Book

36.4. Credits

Bibliography

A. Contributed Scripts

B. A Sed and Awk Micro-Primer

B.1. Sed

B.2. Awk

C. Exit Codes With Special Meanings

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Advanced Bash-Scripting Guide

D. A Detailed Introduction to I/O and I/O Redirection

E. Localization

F. History Commands

G. A Sample .bashrc File

H. Converting DOS Batch Files to Shell Scripts

I. Exercises

I.1. Analyzing Scripts

I.2. Writing Scripts

J. Copyright

List of Tables

11-1. Job Identifiers

31-1. bash options

B-1. Basic sed operators

B-2. Examples

C-1. "Reserved" Exit Codes

H-1. Batch file keywords / variables / operators, and their shell equivalents

H-2. DOS Commands and Their UNIX Equivalents

List of Examples

2-1. cleanup : A script to clean up the log files in /var/log

2-2. cleanup : An enhanced and generalized version of above script.

3-1. exit / exit status

3-2. Negating a condition using !

4-1. Code blocks and I/O redirection

4-2. Saving the results of a code block to a file

4-3. Running a loop in the background

4-4. Backup of all files changed in last day

5-1. Variable assignment and substitution

5-2. Plain Variable Assignment

5-3. Variable Assignment, plain and fancy

5-4. Integer or string?

5-5. Positional Parameters

5-6. wh , whois domain name lookup

5-7. Using shift

6-1. Echoing Weird Variables

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6-2. Escaped Characters

7-1. What is truth?

7-2. Equivalence of test, /usr/bin/test , [ ], and /usr/bin/[

7-3. Arithmetic Tests using (( ))

7-4. arithmetic and string comparisons

7-5. testing whether a string is null

7-6. zmost

8-1. Greatest common divisor

8-2. Using Arithmetic Operations

8-3. Compound Condition Tests Using && and ||

8-4. Representation of numerical constants:

9-1. $IFS and whitespace

9-2. Timed Input

9-3. Once more, timed input

9-4. Timed read

9-5. Am I root?

9-6. arglist : Listing arguments with $* and $@

9-7. Inconsistent $* and $@ behavior

9-8. $* and $@ when $IFS is empty

9-9. underscore variable

9-10. Converting graphic file formats, with filename change

9-11. Alternate ways of extracting substrings

9-12. Using param substitution and :

9-13. Length of a variable

9-14. Pattern matching in parameter substitution

9-15. Renaming file extensions:

9-16. Using pattern matching to parse arbitrary strings

9-17. Matching patterns at prefix or suffix of string

9-18. Using declare to type variables

9-19. Indirect References

9-20. Passing an indirect reference to awk

9-21. Generating random numbers

9-22. Rolling the die with RANDOM

9-23. Reseeding RANDOM

9-24. Pseudorandom numbers, using awk

9-25. C-type manipulation of variables

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Linux - Advanced Bash Shell Scripting Guide.pdf

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