`cat /dev/urandom | od -N 1 -An -i` gives you a uniform random number between 0 and 255. The following mod 10 in the awk command introduces "modulo bias", which you can read about here https://research.kudelskisecurity.com/2020/07/28/the-definit...

You can see it quite intuitively if you iterate over all possible numbers between 0 and 255:

  $ (for i in {0..255}; do; echo $i | awk '{print $1 % 10 + 1}'; done) | sort -n | uniq -c
     26 1
     26 2
     26 3
     26 4
     26 5
     26 6
     25 7
     25 8
     25 9
     25 10