Finding a user's ID on macOS
If you want to know a users uid on macOS or OS X you can use the
directory service command line utility as follows:
dscl . -read /Users/john UniqueID
Which reports in my case:
UniqueID: 501
Another option is to use:
ls -n /Users | grep john
Which, reports in my case
drwxr-xr-x+ 46 501 20 1564 May 31 21:26 john