Question: I have a script where I keep time of when I start and finish. This code works on Linux, but not on my MacOS Sierra v 10.12.6

```
start=`date +"%a %b %d %Y %r"`
end=`date +"%a %b %d %Y %r"`
elapsed_time=`date -d @$(( $(date -d "$end" +%s) - $(date -d "$start" +%s) )) -u +'%H:%M:%S'`

```

The error I get is: 

```
usage: date [-jnRu] [-d dst] [-r seconds] [-t west] [-v[+|-]val[ymwdHMS]] ... 
        [-f fmt date | [[[mm]dd]HH]MM[[cc]yy][.ss]] [+format]
usage: date [-jnRu] [-d dst] [-r seconds] [-t west] [-v[+|-]val[ymwdHMS]] ... 
        [-f fmt date | [[[mm]dd]HH]MM[[cc]yy][.ss]] [+format]
-bash: - : syntax error: operand expected (error token is " ")

```

Is there a way to change this so that it works on my Mac?

Answer: 
**Yes**, you definitely **can track moving surfaces and moving objects** in `ARCore`. 

If you track static surface using `ARCore` – the resulted features are mainly suitable for so-called `Camera Tracking`. If you track moving object/surface – the resulted features are mostly suitable for `Object Tracking`. 

You also can mask moving/not-moving parts of the image and, of course, inverse Six-Degrees-Of-Freedom (translate `xyz` and rotate `xyz`) camera transform.

> 
> Watch [this video](https://www.reddit.com/r/oculus/comments/70tz8p/instead_of_tracking_the_static_environment_in/) to find out how they succeeded.
> 
> 
> 

[![enter image description here](https://i.stack.imgur.com/agUy4.jpg)](https://i.stack.imgur.com/agUy4.jpg)
Yes, ARCore tracks feature points, estimates surfaces, and also allows access to the image data from the camera, so custom computer vision algorithms can be written as well.