Ruby/File Directory/truncate

f = "log.messages"          # Filename
File.truncate(f, 0)         # Erase all existing content

filename = "truncate.txt"
f = open(filename, "w") do |f|
  f << "this is a test."
end
File.size(filename)               
File.truncate(filename, 30)
File.size(filename)               
open(filename) { |f| f.read }