Using Integrator "path":
> cd pbrt/cornell_box
> make path
patch -i path.patch -o path.pbrt cornell_box.pbrt
patching file path.pbrt (read from cornell_box.pbrt)
~/git/github/rs_pbrt/target/release/examples/rs_pbrt -i path.pbrt
pbrt version 0.4.0 [Detected 8 cores]
Copyright (c)2016-2018 Jan Douglas Bert Walter.
...
Writing image "pbrt.png" with bounds Bounds2 { p_min: Point2 { x: 0, y: 0 }, p_max: Point2 { x: 500, y: 500 } }
mv pbrt.png path.png