I'd like to use a script like this.
...
data "data.dat" d1
let d2 = fits d1 ncontour 5 xfrom 0 xto 5 xstep 0.1 yfrom 0 yto 5 ystep 0.1
...
I think we don't need the "data.z" file if the script works.
Contour blocks could be inlined similarly without "-cdata" output file.
...
data "data.dat" d1
let d2 = fits d1 ncontour 5 xfrom 0 xto 5 xstep 0.1 yfrom 0 yto 5 ystep 0.1
let d3 = contour d2 values 0.1 1 1.5
...