Time to for you to debug.
After your build fails, you need to run a container and bring up a command shell from the most recent docker image displayed in a docker image ls command. You can then “snoop” around and try and locate the “missing” commands. If they are not found, you will need to install them, if you find them then you will need to specify the full path in your Dockerfile.
Check out this post. I provided detailed instructions to another person who had a similar problem.