List of Examples

2.1. cleanup: A script to clean up log files in /var/log

2.2. cleanup: An improved clean-up script

2.3. cleanup: An enhanced and generalized version of above scripts.

3.1. Code blocks and I/O redirection

3.2. Saving the output of a code block to a file

3.3. Running a loop in the background

3.4. Backup of all files changed in last day

4.1. Variable assignment and substitution

4.2. Plain Variable Assignment

4.3. Variable Assignment, plain and fancy

4.4. Integer or string?

4.5. Positional Parameters

4.6. wh, whois domain name lookup

4.7. Using shift

5.1. Echoing Weird Variables

5.2. Escaped Characters

5.3. Detecting key-presses

6.1. exit / exit status

6.2. Negating a condition using !

7.1. What is truth?

7.2. Equivalence of test, /usr/bin/test, [ ], and /usr/bin/[

7.3. Arithmetic Tests using (( ))

7.4. Testing for broken links

7.5. Arithmetic and string comparisons

7.6. Testing whether a string is null

7.7. zmore

8.1. Greatest common divisor

8.2. Using Arithmetic Operations

8.3. Compound Condition Tests Using && and ||

8.4. Representation of numerical constants

8.5. C-style manipulation of variables

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. Using declare to type variables

9.11. Generating random numbers

9.12. Picking a random card from a deck

9.13. Brownian Motion Simulation

9.14. Random between values

9.15. Rolling a single die with RANDOM

9.16. Reseeding RANDOM

9.17. Pseudorandom numbers, using awk

10.1. Inserting a blank line between paragraphs in a text file

10.2. Generating an 8-character “random” string

10.3. Converting graphic file formats, with filename change

10.4. Converting streaming audio files to ogg

10.5. Emulating getopt

10.6. Alternate ways of extracting and locating substrings

10.7. Using parameter substitution and error messages

10.8. Parameter substitution and “usage” messages

10.9. Length of a variable

10.10. Pattern matching in parameter substitution

10.11. Renaming file extensions:

10.12. Using pattern matching to parse arbitrary strings

10.13. Matching patterns at prefix or suffix of string

11.1. Simple for loops

11.2. for loop with two parameters in each [list] element

11.3. Fileinfo: operating on a file list contained in a variable

11.4. Operating on a parameterized file list

11.5. Operating on files with a for loop

11.6. Missing in [list] in a for loop

11.7. Generating the [list] in a for loop with command substitution

11.8. A grep replacement for binary files

11.9. Listing all users on the system

11.10. Checking all the binaries in a directory for authorship

11.11. Listing the symbolic links in a directory

11.12. Symbolic links in a directory, saved to a file

11.13. A C-style for loop

11.14. Using efax in batch mode

11.15. Simple while loop

11.16. Another while loop

11.17. while loop with multiple conditions

11.18. C-style syntax in a while loop

11.19. until loop

11.20. Nested Loop

11.21. Effects of break and continue in a loop

11.22. Breaking out of multiple loop levels

11.23. Continuing at a higher loop level

11.24. Using continue N in an actual task

11.25. Using case

11.26. Creating menus using case

11.27. Using command substitution to generate the case variable

11.28. Simple string matching

11.29. Checking for alphabetic input

11.30. Creating menus using select

11.31. Creating menus using select in a function

12.1. Stupid script tricks

12.2. Generating a variable from a loop

12.3. Finding anagrams

15.1. A script that spawns multiple instances of itself

15.2. printf in action

15.3. Variable assignment, using read

15.4. What happens when read has no variable

15.5. Multi-line input to read

15.6. Detecting the arrow keys

15.7. Using read with file redirection

15.8. Problems reading from a pipe

15.9. Changing the current working directory

15.10. Letting let do arithmetic.

15.11. Showing the effect of eval

15.12. Using eval to select among variables

15.13. Echoing the command-line parameters

15.14. Forcing a log-off

15.15. A version of rot13

15.16. Using set with positional parameters

15.17. Reversing the positional parameters

15.18. Reassigning the positional parameters

15.19. “Unsetting” a variable

15.20. Using export to pass a variable to an embedded awk script

15.21. Using getopts to read the options/arguments passed to a script

15.22. “Including” a data file

15.23. A (useless) script that sources itself

15.24. Effects of exec

15.25. A script that exec's itself

15.26. Waiting for a process to finish before proceeding

15.27. A script that kills itself

16.1. Using ls to create a table of contents for burning a CDR disk

16.2. Hello or Good-bye

16.3. Badname, eliminate file names in current directory containing bad characters and whitespace.

16.4. Deleting a file by its inode number

16.5. Logfile: Using xargs to monitor system log

16.6. Copying files in current directory to another

16.7. Killing processes by name

16.8. Word frequency analysis using xargs

16.9. Using expr

16.10. Using date

16.11. Date calculations

16.12. Word Frequency Analysis

16.13. Which files are scripts?

16.14. Generating 10-digit random numbers

16.15. Using tail to monitor the system log

16.16. Printing out the From lines in stored e-mail messages

16.17. Emulating grep in a script

16.18. Crossword puzzle solver

16.19. Looking up definitions in Webster's 1913 Dictionary

16.20. Checking words in a list for validity

16.21. toupper: Transforms a file to all uppercase.

16.22. lowercase: Changes all filenames in working directory to lowercase.

16.23. du: DOS to UNIX text file conversion.

16.24. rot13: ultra-weak encryption.

16.25. Generating “Crypto-Quote” Puzzles

16.26. Formatted file listing.

16.27. Using column to format a directory listing

16.28. nl: A self-numbering script.

16.29. manview: Viewing formatted manpages

16.30. Using cpio to move a directory tree

16.31. Unpacking an rpm archive

16.32. Stripping comments from C program files

16.33. Exploring /usr/X11R6/bin

16.34. An “improved” strings command

16.35. Using cmp to compare two files within a script.

16.36. basename and dirname

16.37. A script that copies itself in sections

16.38. Checking file integrity

16.39. Uudecoding encoded files

16.40. Finding out where to report a spammer

16.41. Analyzing a spam domain

16.42. Getting a stock quote

16.43. Updating FC4

16.44. Using ssh

16.45. A script that mails itself

16.46. Generating prime numbers

16.47. Monthly Payment on a Mortgage

16.48. Base Conversion

16.49. Invoking bc using a here document

16.50. Calculating PI

16.51. Converting a decimal number to hexadecimal

16.52. Factoring

16.53. Calculating the hypotenuse of a triangle

16.54. Using seq to generate loop arguments

16.55. Letter Count"

16.56. Using getopt to parse command-line options

16.57. A script that copies itself

16.58. Exercising dd

16.59. Capturing Keystrokes

16.60. Preparing a bootable SD card for the Raspberry Pi

16.61. Securely deleting a file

16.62. Filename generator

16.63. Converting meters to miles

16.64. Using m4

17.1. Setting a new password

17.2. Setting an erase character

17.3. secret password: Turning off terminal echoing

17.4. Keypress detection

17.5. Checking a remote server for identd

17.6. pidof helps kill a process

17.7. Checking a CD image

17.8. Creating a filesystem in a file

17.9. Adding a new hard drive

17.10. Using umask to hide an output file from prying eyes

17.11. Backlight: changes the brightness of the (laptop) screen backlight

17.12. killall, from /etc/rc.d/init.d

19.1. broadcast: Sends message to everyone logged in

19.2. dummyfile: Creates a 2-line dummy file

19.3. Multi-line message using cat

19.4. Multi-line message, with tabs suppressed

19.5. Here document with replaceable parameters

19.6. Upload a file pair to Sunsite incoming directory

19.7. Parameter substitution turned off

19.8. A script that generates another script

19.9. Here documents and functions

19.10. “Anonymous” Here Document

19.11. Commenting out a block of code

19.12. A self-documenting script

19.13. Prepending a line to a file

19.14. Parsing a mailbox

20.1. Redirecting stdin using exec

20.2. Redirecting stdout using exec

20.3. Redirecting both stdin and stdout in the same script with exec

20.4. Avoiding a subshell

20.5. Redirected while loop

20.6. Alternate form of redirected while loop

20.7. Redirected until loop

20.8. Redirected for loop

20.9. Redirected for loop (both stdin and stdout redirected)

20.10. Redirected if/then test

20.11. Data file names.data for above examples

20.12. Logging events

21.1. Variable scope in a subshell

21.2. List User Profiles

21.3. Running parallel processes in subshells

22.1. Running a script in restricted mode

23.1. Code block redirection without forking

23.2. Redirecting the output of process substitution into a loop.

24.1. Simple functions

24.2. Function Taking Parameters

24.3. Functions and command-line args passed to the script

24.4. Passing an indirect reference to a function

24.5. Dereferencing a parameter passed to a function

24.6. Again, dereferencing a parameter passed to a function

24.7. Maximum of two numbers

24.8. Converting numbers to Roman numerals

24.9. Testing large return values in a function

24.10. Comparing two large integers

24.11. Real name from username

24.12. Local variable visibility

24.13. Demonstration of a simple recursive function

24.14. Another simple demonstration

24.15. Recursion, using a local variable

24.16. The Fibonacci Sequence

24.17. The Towers of Hanoi

25.1. Aliases within a script

25.2. unalias: Setting and unsetting an alias

26.1. Using an and list to test for command-line arguments

26.2. Another command-line arg test using an and list

26.3. Using or lists in combination with an and list

27.1. Simple array usage

27.2. Formatting a poem

27.3. Various array operations

27.4. String operations on arrays

27.5. Loading the contents of a script into an array

27.6. Some special properties of arrays

27.7. Of empty arrays and empty elements

27.8. Initializing arrays

27.9. Copying and concatenating arrays

27.10. More on concatenating arrays

27.11. The Bubble Sort

27.12. Embedded arrays and indirect references

27.13. The Sieve of Eratosthenes

27.14. The Sieve of Eratosthenes, Optimized

27.15. Emulating a push-down stack

27.16. Complex array application: Exploring a weird mathematical series

27.17. Simulating a two-dimensional array, then tilting it

28.1. Indirect Variable References

28.2. Passing an indirect reference to awk

29.1. Using /dev/tcp for troubleshooting

29.2. Playing music

29.3. Finding the process associated with a PID

29.4. On-line connect status

30.1. Print the server environment

30.2. IP addresses

31.1. Hiding the cookie jar

31.2. Setting up a swapfile using /dev/zero

31.3. Creating a ramdisk

32.1. A buggy script

32.2. Missing keyword

32.3. test24: another buggy script

32.4. Testing a condition with an assert

32.5. Trapping at exit

32.6. Cleaning up after Control-C

32.7. A Simple Implementation of a Progress Bar

32.8. Tracing a variable

32.9. Running multiple processes (on an SMP box)

34.1. Numerical and string comparison are not equivalent

34.2. Subshell Pitfalls

34.3. Piping the output of echo to a read

36.1. shell wrapper

36.2. A slightly more complex shell wrapper

36.3. A generic shell wrapper that writes to a logfile

36.4. A shell wrapper around an awk script

36.5. A shell wrapper around another awk script

36.6. Perl embedded in a Bash script

36.7. Bash and Perl scripts combined

36.8. Python embedded in a Bash script

36.9. A script that speaks

36.10. A (useless) script that recursively calls itself

36.11. A (useful) script that recursively calls itself

36.12. Another (useful) script that recursively calls itself

36.13. A “colorized” address database

36.14. Drawing a box

36.15. Echoing colored text

36.16. A “horserace” game

36.17. A Progress Bar

36.18. Return value trickery

36.19. Even more return value trickery

36.20. Passing and returning arrays

36.21. Fun with anagrams

36.22. Widgets invoked from a shell script

36.23. Test Suite

37.1. String expansion

37.2. Indirect variable references - the new way

37.3. Simple database application, using indirect variable referencing

37.4. Using arrays and other miscellaneous trickery to deal four random hands from a deck of cards

37.5. A simple address database

37.6. A somewhat more elaborate address database

37.7. Testing characters

37.8. Reading N characters

37.9. Using a here document to set a variable

37.10. Piping input to a read

37.11. Negative array indices

37.12. Negative parameter in string-extraction construct

A.1. mailformat: Formatting an e-mail message

A.2. rn: A simple-minded file renaming utility

A.3. blank-rename: Renames filenames containing blanks

A.4. encryptedpw: Uploading to an ftp site, using a locally encrypted password

A.5. copy-cd: Copying a data CD

A.6. Collatz series

A.7. days-between: Days between two dates

A.8. Making a dictionary

A.9. Soundex conversion

A.10. Game of Life

A.11. Data file for Game of Life

A.12. behead: Removing mail and news message headers

A.13. password: Generating random 8-character passwords

A.14. fifo: Making daily backups, using named pipes

A.15. Generating prime numbers using the modulo operator

A.16. tree: Displaying a directory tree

A.17. tree2: Alternate directory tree script

A.18. string functions: C-style string functions

A.19. Directory information

A.20. Library of hash functions

A.21. Colorizing text using hash functions

A.22. More on hash functions

A.23. Mounting USB keychain storage devices

A.24. Converting to HTML

A.25. Preserving weblogs

A.26. Protecting literal strings

A.27. Unprotecting literal strings

A.28. Spammer Identification

A.29. Spammer Hunt

A.30. Making wget easier to use

A.31. A podcasting script

A.32. Nightly backup to a firewire HD

A.33. An expanded cd command

A.34. A soundcard setup script

A.35. Locating split paragraphs in a text file

A.36. Insertion sort

A.37. Standard Deviation

A.38. A pad file generator for shareware authors

A.39. A man page editor

A.40. Petals Around the Rose

A.41. Quacky: a Perquackey-type word game

A.42. Nim

A.43. A command-line stopwatch

A.44. An all-purpose shell scripting homework assignment solution

A.45. The Knight's Tour

A.46. Magic Squares

A.47. Fifteen Puzzle

A.48. The Towers of Hanoi, graphic version

A.49. The Towers of Hanoi, alternate graphic version

A.50. An alternate version of the getopt-simple.sh script

A.51. The version of the UseGetOpt.sh example used in the Tab Expansion appendix

A.52. Cycling through all the possible color backgrounds

A.53. Morse Code Practice

A.54. Base64 encoding/decoding

A.55. Inserting text in a file using sed

A.56. The Gronsfeld Cipher

A.57. Bingo Number Generator

A.58. Basics Reviewed

A.59. Testing execution times of various commands

A.60. Associative arrays vs. conventional arrays (execution times)

C.1. Counting Letter Occurrences

J.1. Completion script for UseGetOpt.sh

M.1. Sample .bashrc file

M.2. .bash_profile file

N.1. VIEWDATA.BAT: DOS Batch File

N.2. viewdata.sh: Shell Script Conversion of VIEWDATA.BAT

T.1. A script that generates an ASCII table

T.2. Another ASCII table script

T.3. A third ASCII table script, using awk