From: Suraj Kurapati <snk@...>
Date: 2008-05-14T07:08:00+09:00
Subject: Re: Switch Two Lines in a File

Dana Merrick wrote:
> I'm providing two regexes, and the
> script is to replace a line that matches one regex with a line that
> matches the other.

Here's my solution; thanks for the fun exercise.

$ cat foo
line three
line two
line one
another one
another three

$ ruby -v switch.rb foo
ruby 1.8.6 (2007-09-24 patchlevel 111) [i686-linux]
line one
line two
line three
another three
another one

$ cat switch.rb
firstQuery = /one/
secondQuery = /three/

# determine line numbers of matching lines
firstIndices = []
secondIndices = []

lines = ARGF.readlines
lines.each_with_index do |line, i|
  case line
  when firstQuery
    firstIndices << i
  when secondQuery
    secondIndices << i
  end
end

# swap all matching lines
firstIndices.zip(secondIndices).each do |(a, b)|
  lines[a], lines[b] = lines[b], lines[a]
end

puts lines
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