Британские ученые text maker

gistfile1.rb

str = "Today we (professors + teaching assistants) proctored a midterm exam for a class of about 80 students. There was undoubtedly a 'hardest' question on the exam, since nearly the entire classroom of students asked us how to proceed with that question. To be fair, we didn't give any hints, but it was clear that one had to use a definition to be able to proceed."

res = str.gsub(/\b[[:alpha:]]+\b/) do |word|
  if word.length < 4
    word
  else
    word[0] + # first letter
       word[1..-2].chars.shuffle.join('') +
       word[-1] # last letter
  end
end

puts res