`od -N 1 -An -i` reads one byte from stdin (urandom in this case) and prints it as a decimal string (with value between 0 and 255). The awk command receives tha

`od -N 1 -An -i` reads one byte from stdin (urandom in this case) and prints it as a decimal string (with value between 0 and 255). The awk command receives that number and prints it back out modulo 10.