Disk/usbDrive speed test

Phoronix Test Suite (PTS) is a command line test suite which has been created for benchmarking systems. It includes multiple free open source utilities that can be used (each must be downloaded separately through the PTS utility). They work well on Linux, but are a little problematic at times on Macs, since some of the utilities are not available for the Mac and others just don't seem to work (at least I've never had the time to figure out why some don't work on a Mac even though they are listed as available). I believe there are about three or four disk based utilities that actually will work on macOS from PTS.

Setting up & using Phoronix Test Suite can be a bit difficult as some details are not included in the setup instructions (or it can be hard to locate some details especially if you are trying to customize things). To test an external drive requires having PTS on the external drive (the drive to be tested).

Once PTS is installed, everything else is downloaded & installed into the PTS folder unless configured otherwise. I don't recall if the PTS installer actually modified macOS at all since I always used it from a special external macOS boot drive I created for testing Macs so I wasn't concerned about any macOS modifications. I think any modifications are slight. I may not even have used the PTS installer.

There may be a couple of native macOS command line utilities that can be used, but I don't think they are very good options since they are usually very limited. I don't recall since I found it easier to use PTS.

Any other command line options will unfortunately potentially affect your macOS installation, so it is best to avoid them unless you create & use an external macOS boot drive so your main macOS boot drive is not affected. You may want to research PTS a bit more to see if it makes any changes to macOS since it has been a while since I used it myself.

when I want to check a disk's speed, I use Blackmagic Disk Speed Test. it's available in the App Store for free.

if you are married to using terminal, you will need to wait for someone that can tell you if and how it can be done.