# File escape.rb, line 65
  def shell_single_word(str)
    if str.empty?
      "''"
    elsif %r{\A[0-9A-Za-z+,./:=@_-]+\z} =~ str
      str
    else
      result = ''
      str.scan(/('+)|[^']+/) {
        if $1
          result << %q{\'} * $1.length
        else
          result << "'#{$&}'"
        end
      }
      result
    end
  end