Advanced Bash−Scripting Guide

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For a more extensive treatment of sed, check the appropriate references in the Bibliography. B.2. Awk Advanced Bash−Scripting Guide Awk is a full−featured text processing language with a syntax reminiscent of C. While it possesses an extensive set of operators and capabilities, we will cover only a couple of these here − the ones most useful for shell scripting. Awk breaks each line of input passed to it into fields. By default, a field is a string of consecutive characters separated by whitespace, though there are options for changing the delimiter. Awk parses and operates on each separate field. This makes awk ideal for handling structured text files, especially tables, data organized into consistent chunks, such as rows and columns. Strong quoting (single quotes) and curly brackets enclose segments of awk code within a shell script. awk '{print $3}' $filename # Prints field #3 of file $filename to stdout. awk '{print $1 $5 $6}' $filename # Prints fields #1, #5, and #6 of file $filename. We have just seen the awk print command in action. The only other feature of awk we need to deal with here is variables. Awk handles variables similarly to shell scripts, though a bit more flexibly. { total += ${column_number} } This adds the value of column_number to the running total of "total". Finally, to print "total", there is an END command block, executed after the script has processed all its input. END { print total } Corresponding to the END, there is a BEGIN, for a code block to be performed before awk starts processing its input. For examples of awk within shell scripts, see: 1. Example 11−10 2. Example 16−7 3. Example 12−24 4. Example 34−3 5. Example 9−22 6. Example 11−16 7. Example 28−1 8. Example 28−2 9. Example 10−3 10. Example 12−42 11. Example 9−26 12. Example 12−3 13. Example 9−12 14. Example 34−11 15. Example 10−8 Appendix B. A Sed and Awk Micro−Primer 410
Advanced Bash−Scripting Guide That's all the awk we'll cover here, folks, but there's lots more to learn. See the appropriate references in the Bibliography. Appendix B. A Sed and Awk Micro−Primer 411
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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 $file ]] then echo "Pass
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Advanced Bash−Scripting Guide −
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7.3. Comparison operators (binary)
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Example 7−5. arithmetic and strin
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Chapter 8. Operations and Related T
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Part 3. Beyond the Basics Table of
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$EDITOR the default editor invoked
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Advanced Bash−Scripting Guide (Th
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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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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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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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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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#!/bin/bash # color−echo.sh: Echo
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34.7. Assorted Tips Advanced Bash
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Advanced Bash−Scripting Guide •
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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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Page 369 and 370: Bibliography Edited by Peter Dennin
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Page 373 and 374: Mark Komarinski's Printing−Usage
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Page 389 and 390: let "row = $r" # Count center row o
Page 391 and 392: next_gen "$Cur" let "generation +=
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Page 403 and 404: # ListDirectory "FileGlob" "Field
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Page 407 and 408: The md5sum program is documented as
Page 409 and 410: Note: 'mount −l' does return the
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Page 413 and 414: Appendix B. A Sed and Awk Micro−P
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Page 419 and 420: Appendix D. A Detailed Introduction
Page 421 and 422: Appendix E. Localization Localizati
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Page 435 and 436: Appendix H. Converting DOS Batch Fi
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Page 439 and 440: Appendix I. Exercises I.1. Analyzin
Page 441 and 442: Lottery Numbers One type of lottery
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Page 451 and 452: # Thanks to Stephane Chazelas for p
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