string variable for markup

[Stephen MacNeil]

how would i get the input string to attach to a markup?

eg

\version "2.18.2"

acdy =

\markup \pad-markup #.5 \halign #-1.3

{ \combine

\draw-line #'($str . .5) \draw-line #'($str . -.5)

}

The idea is to be able to assign  a length $str

thanks

Stephen