(
  tr -dc 'A-Z' </dev/urandom 2>/dev/null | head -c1;         # One random uppercase letter
  tr -dc 'a-z' </dev/urandom 2>/dev/null | head -c1;         # One random lowercase letter
  tr -dc '0-9' </dev/urandom 2>/dev/null | head -c1;         # One random digit Read more about password generator