Do plain string replace (use string#gsub API) of a collection of files

files_content_replace.rb

#!/usr/bin/env ruby
# encoding: utf-8 
#
#Usage: ruby files_content_replace.rb <filePathLists.txt>

File.open(ARGV[0]).each { |filePath|
  correctedFileContentLines = []
    f = File.open(filePath.strip)
    f.each { |line|
        line2 = line.gsub("old text", "new text")
        if line2!=line then
            puts "#{line} => #{line2}"
        end
        correctedFileContentLines.push line2
    }
    f.close #Must close it before write new content;

    File.new(filePath.strip, "w").write( correctedFileContentLines.join )
}