Break a long line
Align

on emacs:
  M-x aligne-regexp RET => RET
Use constant instead of global variable.

This variable is not modified.
Remove needless "then".
Use embeded expression in string literal
Use case-when expression
Use embeded expression in string literal
Use case-when expression
Use embeded expression in string literal
Use %Q string literal.

This makes easy to embed double quote in string.
Use ARGF instead of STDIN.

Before:
  ruby mk_column_defs.rb < hosts.dat

After:
  ruby mk_column_defs.rb hosts.dat

See also:
http://doc.ruby-lang.org/ja/1.9.3/class/ARGF=2eclass.html
Delete trailing white spaces
Merge pull request #5 from okkez/use-rubyish-style

Use rubyish style