regular_expressions.rb

# Determine whether a string contains a Social Security number.
def has_ssn?(string)
  string =~ /\d{3}-\d{2}-\d{4}/
end

# Return the Social Security number from a string.
def grab_ssn(string)
  grab_all_ssns(string).first
end

# Return all of the Social Security numbers from a string.
def grab_all_ssns(string)
  string.scan(/\d{3}-\d{2}-\d{4}/)
end

# Obfuscate all of the Social Security numbers in a string. Example: XXX-XX-4430.
def hide_all_ssns(string)
  if has_ssn?(string)
    ssns = grab_all_ssns(string)
    ssns.each do |ssn|
     ssn.gsub!(/(\d{3})-(\d{2})/, 'XXX-XX')
    end
    ssns.join(', ')
  else
    string
  end
end

# Ensure all of the Social Security numbers use dashes for delimiters.
# Example: 480.01.4430 and 480014430 would both be 480-01-4430.
def format_ssns(string)
  string.gsub(/(\d{3})\D*(\d{2})\D*(\d{4})/, '\1-\2-\3')
end