This simple programm removes some characters or words and pastes new one instead.
It can be helpfull, when it is necessary to change, for example, 1 tab to 2 spaces in a whole document or in a bunch of files (e.g. in a whole project or folder). 

Using:

  $ ruby replacer.rb controllers/ - to change files in whole directory
  $ ruby replacer.rb 1.txt 2.txt - to change only these files

Then programm asks you 3 questions:
1. what character do you want to remove
2. what character do you want to paste instead.
3. what types of files do you want to edit (js,rb,html,haml etc)

Good luck.