プロ生ちゃんのカレンダーのあれ (Ruby) ref: http://qiita.com/zakuroishikuro/items/6a1cdc48609875b8e131

file0.txt

require 'date'

last = Date.new(Time.now.year, Time.now.month, -1)

days = (1..last.day).map{|d| '%2d' % d}
days.unshift *[nil] * (last + 1 << 1).wday

puts last.strftime "%B %Y"
puts days.each_slice(7).map{|week| week * "\t"}

file1.txt

January 2015
                 1   2   3
 4   5   6   7   8   9  10
11  12  13  14  15  16  17
18  19  20  21  22  23  24
25  26  27  28  29  30  31