# File Tail
# By Ashok Menon
# 11-11-2010
# Given two files, and a percentage [x], will copy the last x% of the first file, into the second file

abort "Incorrect Number of Arguments.\nFormat: \"ruby file-tail.rb [first-file] [second-file] [percent=30]\"" if !([2,3].include? ARGV.length)

first_file_path = ARGV[0]; second_file_path = ARGV[1]

if ARGV.length == 3
  percent = ( ARGV[2].to_f ) / 100.0
else
  percent = 0.3
end

abort "First File Does Not Exist." if !(File.exists? first_file_path)

first_file = File.new first_file_path
second_file = File.new (second_file_path), "w+"

file_lines = first_file.readlines
line_no = file_lines.length
tail_length = (line_no*percent).round
upperbound = line_no - 1
lowerbound = upperbound - tail_length

file_lines[lowerbound..upperbound].each do |line|
  second_file.puts line
end