Advanced Bash−Scripting Guide

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Advanced Bash−Scripting Guide Jones,Bill,235 S. Williams St.,Denver,CO,80221,(303) 244−7989 Smith,Tom,404 Polk Ave.,Los Angeles,CA,90003,(213) 879−5612 ... Reformat the data and print it out to stdout in labeled, evenly−spaced columns. Justification Given ASCII text input either from stdin or a file, by adjusting the word spacing right−justify each line to a user−specified line−width and send the output to stdout. Mailing List Using the mail command, write a script that manages a simple mailing list. The script automatically e−mails the monthly company newsletter, read from a specified text file, and sends it to all the addresses on the mailing list, which the script reads from another specified file. Passwords Generate pseudorandom 8−character passwords, using characters in the ranges [0−9], [A−Z], [a−z]. Each password must contain at least two digits. Difficult Logging File Accesses Log all accesses to the files in /etc during the course of a single day. This information should include the filename, user name, and access time. If any alterations to the files take place, that should be flagged. Write this data as neatly formatted records in a logfile. Strip Comments Strip all comments from a shell script whose name is specified on the command line. Note that the "#! line" must not be stripped out. HTML Conversion Convert a given text file to HTML. This non−interactive script automatically inserts all appropriate HTML tags into a file specified as an argument. Strip HTML Tags Strip all HTML tags from a specified HTML file, then reformat it into lines between 60 and 75 characters in length. Reset paragraph and block spacing, as appropriate, and convert HTML tables to their approximate text equivalent. XML Conversion Convert an XML file to both HTML and text format. Chasing Spammers Write a script that analyzes a spam e−mail by doing DNS lookups on the IP addresses in the headers to identify the relay hosts as well as the originating ISP. The script will forward the unaltered spam message to the responsible ISPs. Of course, it will be necessary to filter out your own ISP's IP address, so you don't end up complaining about yourself. As necessary, use the appropriate network analysis commands. Morse Code Convert a text file to Morse code. Each character of the text file will be represented as a corresponding Morse code group of dots and dashes (underscores), separated by whitespace from the next. For example, "script" ===> "... _._. ._. .. .__. _". Hex Dump Do a hex(adecimal) dump on a binary file specified as an argument. The output should be in neat tabular fields, with the first field showing the address, each of the next 8 fields a 4−byte hex number, and the final field the ASCII equivalent of the previous 8 fields. Emulating a Shift Register Appendix I. Exercises 436
Advanced Bash−Scripting Guide Using Example 26−8 as an inspiration, write a script that emulates a 64−bit shift register as an array. Implement functions to load the register, shift left, and shift right. Finally, write a function that interprets the register contents as eight 8−bit ASCII characters. Determinant Solve a 4 x 4 determinant. Hidden Words Write a "word−find" puzzle generator, a script that hides 10 input words in a 10 x 10 matrix of random letters. The words may be hidden across, down, or diagonally. Anagramming Anagram 4−letter input. For example, the anagrams of word are: do or rod row word. You may use /usr/share/dict/linux.words as the reference list. Fog Index The "fog index" of a passage of text estimates its reading difficulty, as a number corresponding roughly to a school grade level. For example, a passage with a fog index of 12 should be comprehensible to anyone with 12 years of schooling. The Gunning version of the fog index uses the following algorithm. 1. Choose a section of the text at least 100 words in length. 2. Count the number of sentences (a portion of a sentence truncated by the boundary of the text section counts as one). 3. Find the average number of words per sentence. AVE_WDS_SEN = TOTAL_WORDS / SENTENCES 4. Count the number of "difficult" words in the segment −− those containing at least 3 syllables. Divide this quantity by total words to get the proportion of difficult words. PRO_DIFF_WORDS = LONG_WORDS / TOTAL_WORDS 5. The Gunning fog index is the sum of the above two quantities, multiplied by 0.4, then rounded to the nearest integer. G_FOG_INDEX = int ( 0.4 * ( AVE_WDS_SEN + PRO_DIFF_WORDS ) ) Step 4 is by far the most difficult portion of the exercise. There exist various algorithms for estimating the syllable count of a word. A rule−of−thumb formula might consider the number of letters in a word and the vowel−consonant mix. A strict interpretation of the Gunning Fog index does not count compound words and proper nouns as "difficult" words, but this would enormously complicate the script. Calculating PI using Buffon's Needle The Eighteenth Century French mathematician de Buffon came up with a novel experiment. Repeatedly drop a needle of length "n" onto a wooden floor composed of long and narrow parallel boards. The cracks separating the equal−width floorboards are a fixed distance "d" apart. Keep track of the total drops and the number of times the needle intersects a crack on the floor. The ratio of these two quantities turns out to be a fractional multiple of PI. In the spirit of Example 12−35, write a script that runs a Monte Carlo simulation of Buffon's Needle. To simplify matters, set the needle length equal to the distance between the cracks, n = d. Hint: there are actually two critical variables: the distance from the center of the needle to the nearest crack to it, and the angle of the needle to that crack. You may use bc to handle the calculations. Playfair Cipher Appendix I. Exercises 437
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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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Advanced Bash−Scripting Guide OUT
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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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Advanced Bash−Scripting Guide # r
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Advanced Bash−Scripting Guide gre
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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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Advanced Bash−Scripting Guide 16.
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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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Chapter 20. Subshells Running a she
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# Range: 0 − 200 # It's crude, bu
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# grep PATTERN /etc/passwd | awk
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Advanced Bash−Scripting Guide # Y
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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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echo ${colors[$index]} let "index =
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# Replace all matching wildcarded s
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fi let "t += $i " Primes[t]=$NON_PR
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# −−−−−−−−− # 1)
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Chapter 28. /dev and /proc A Linux
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Advanced Bash−Scripting Guide # A
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Chapter 30. Debugging The Bash shel
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4. Advanced Bash−Scripting Guide
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Chapter 31. Options Options are set
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Chapter 32. Gotchas Turandot: Gli e
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command1 2> − | command2 # Trying
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echo "one two three" | read a b c #
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Chapter 33. Scripting With Style Ge
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#!/bin/bash # color−echo.sh: Echo
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34.7. Assorted Tips Advanced Bash
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# agram.sh: Playing games with anag
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Chapter 35. Bash, version 2 The cur
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1−56592−580−7). This is the s
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Bibliography Edited by Peter Dennin
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Mark Komarinski's Printing−Usage
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let "row = $r" # Count center row o
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Page 419 and 420: Appendix D. A Detailed Introduction
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