Advanced Bash−Scripting Guide

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12.8. Math Commands "Doing the numbers" Advanced Bash−Scripting Guide factor Decompose an integer into prime factors. bash$ factor 27417 27417: 3 13 19 37 bc Bash can't handle floating point calculations, and it lacks operators for certain important mathematical functions. Fortunately, bc comes to the rescue. Not just a versatile, arbitrary precision calculation utility, bc offers many of the facilities of a programming language. bc has a syntax vaguely resembling C. Since it is a fairly well−behaved UNIX utility, and may therefore be used in a pipe, bc comes in handy in scripts. Here is a simple template for using bc to calculate a script variable. This uses command substitution. variable=$(echo "OPTIONS; OPERATIONS" | bc) Example 12−32. Monthly Payment on a Mortgage #!/bin/bash # monthlypmt.sh: Calculates monthly payment on a mortgage. # This is a modification of code in the "mcalc" (mortgage calculator) package, # by Jeff Schmidt and Mendel Cooper (yours truly, the author of this document). # http://www.ibiblio.org/pub/Linux/apps/financial/mcalc−1.6.tar.gz [15k] echo echo "Given the principal, interest rate, and term of a mortgage," echo "calculate the monthly payment." bottom=1.0 echo echo −n "Enter principal (no commas) " read principal echo −n "Enter interest rate (percent) " # If 12%, enter "12", not ".12". read interest_r echo −n "Enter term (months) " read term interest_r=$(echo "scale=9; $interest_r/100.0" | bc) # Convert to decimal. # "scale" determines how many decimal places. Chapter 12. External Filters, Programs and Commands 196
Advanced Bash−Scripting Guide interest_rate=$(echo "scale=9; $interest_r/12 + 1.0" | bc) top=$(echo "scale=9; $principal*$interest_rate^$term" | bc) echo; echo "Please be patient. This may take a while." let "months = $term − 1" # ==================================================================== for ((x=$months; x > 0; x−−)) do bot=$(echo "scale=9; $interest_rate^$x" | bc) bottom=$(echo "scale=9; $bottom+$bot" | bc) # bottom = $(($bottom + $bot")) done # −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− # Rick Boivie pointed out a more efficient implementation #+ of the above loop, which decreases computation time by 2/3. # for ((x=1; x
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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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Advanced Bash−Scripting Guide Exa
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Advanced Bash−Scripting Guide MIN
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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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Advanced Bash−Scripting Guide (Th
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Advanced Bash−Scripting Guide #!/
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Example 9−2. Timed Input Advanced
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Advanced Bash−Scripting Guide fi
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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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Advanced Bash−Scripting Guide ###
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# Accept upper or lowercase input.
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Advanced Bash−Scripting Guide a=`
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# May need to also press ENTER if a
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Page 155 and 156: cat, tac # Burn the CDR. cdrecord
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Page 159 and 160: exit $E_CHANGED_MIND ;; *) echo "De
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Page 201: mailto Similar to the mail command,
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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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Advanced Bash−Scripting Guide alt
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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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Advanced Bash−Scripting Guide # =
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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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Advanced Bash−Scripting Guide tpu
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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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Advanced Bash−Scripting Guide # R
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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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Advanced Bash−Scripting Guide pad
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let "row = $r" # Count center row o
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next_gen "$Cur" let "generation +=
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[−c localdirectory] [−m filepat
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Advanced Bash−Scripting Guide #:d
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# ListDirectory "FileGlob" "Field
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Advanced Bash−Scripting Guide # I
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The md5sum program is documented as
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Note: 'mount −l' does return the
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Advanced Bash−Scripting Guide dec
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Appendix B. A Sed and Awk Micro−P
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Advanced Bash−Scripting Guide Tha
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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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Advanced Bash−Scripting Guide and
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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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