I want to duplicate a number of boxes along a curve every certain distance.
so i want to get the length of the curve,how to get it?
thanks

measure sop?

You can get the length of a curve primitive with the arclen expression function. Example:
arclen(“../curve1”, 0, 0, 1)
You could also use a Resample SOP after the curve, choose the Maximum Segment Length option, specify a segment length, and use the resampled curve as a template geometry (second input) in the Copy SOP, using the box you wish to duplicate along the curve as the first input of the Copy SOP.

Great! Thank you very much