cut a field of csv file.

cut_f.rb

# encodings: utf-8
=begin :rdoc

= cut_f.rb

This script prints a field of CSV file.

The format of the csv file is the following
id, replied_to_id, thread_id, timestamp, group, recipients, private, user_id, user, email_address, body, url, attachment_ids

= usage 

  ruby cut_f.rb field-number  <csv-file> 

= output 

  print n-th field

Author :: hirotaka.yoshioka@mail.rakuten.com 
Date   :: 6/2/2011 created 

= history
 06/02/2011 initial

=end

require 'csv'

field_num = ARGV[0].to_i
if ARGV[1] == "-" or ARGV[1] == nil
  io = $stdin
else 
  io = File.open(ARGV[1], "r")
end

CSV::Reader.create(io.read).each do |row|
  print row[field_num], "\n"
end