def command_for_ruby_tool(name)
      filename = respond_to?(name) ? send(name) : locate_ruby_tool(name)
      shebang_command(filename) =~ /ruby/ ? "#{ruby_command} #{filename}" : filename
    end
def command_for_ruby_tool(name)
      filename = respond_to?(name) ? send(name) : locate_ruby_tool(name)
      shebang_command(filename) =~ /ruby/ ? "#{ruby_command} #{filename}" : filename
    end
Returns the correct command string for invoking the +name+ executable
 that belongs to the current Ruby interpreter. Returns +nil+ if the
 command is not found.

 If the command executable is a Ruby program, then we need to run it
 in the correct Ruby interpreter just in case the command doesn't
 have the correct shebang line; we don't want a totally different
 Ruby than the current one to be invoked.