[LINUX] I tried to create Bulls and Cows with a shell program

Introduction

I created it as a small story of Bash programming. This is the 6th bullet. This time it was quite tough.

What is Bulls and Cows?

For Bulls and Cows, see Wikipedia and here.

Originally a string guessing game, This time I will create it as a number guessing game.

Source

#!/bin/bash

function chkAns {
  bull=0
  cow=0
  num=$1
  dig=$2
  ans=$3

  for i in $(seq 1 $dig)
  do
    for j in $(seq 1 $dig)
    do
      if [[ ${num:i:1} == ${ans:j:1} && $i == $j ]]
      then
#       echo bull: $bull        #for debug
        (( bull = bull + 1 ))
      elif [[ ${num:i:1} == ${ans:j:1} && $i != $j ]]
      then
#       echo cow: $cow          #for debug
        (( cow = cow + 1 ))
      fi
    done
  done

  if (( bull == dig ))
  then
    echo -e "$dig bulls ! You did it !"
    exit
  else
    echo -e "$bull bull and $cow cow."
  fi
}

echo "Welcome 'Bulls and Cows' Game"
echo -e "Please input digits of numbers => \c"
read digits

tmp=$(shuf -i 0-9 -n $digits -z)
answer=${tmp:0:3}

#echo $answer  #for debug

for k in $(seq 1 10)
do
  echo -e "Input $digits numbers of your answer. (${k} time) => \c"
  read num

  chkAns $num $digits $answer
  if (( $k == 10 ))
  then
    echo "You failed 10 times..."
  fi
done

echo -e "The answer is '$answer'"

$ RANDOM was fine, but I didn't use it because I don't trust it. Instead, I used the shuf command.

Execution result (correct answer)

$ ./bulls_and_cows.sh
Welcome 'Bulls and Cows' Game
Please input digits of numbers => 3
./bulls_and_cows.sh:Line 39:warning: command substitution: ignored null byte in input
Input 3 numbers of your answer. (1 time) => 321
2 bull and 0 cow.
Input 3 numbers of your answer. (2 time) => 324
2 bull and 0 cow.
Input 3 numbers of your answer. (3 time) => 325
3 bulls ! You did it !

The "Warning: command substitution: ignored null byte in input" message seems to come out when it contains null bytes. However, I'm ignoring it because it was difficult to generate N digits without using Null. Please comment if there is a good solution.

Execution result (fails)

~~ I'm seriously trying to answer correctly. ~~

$ ./bulls_and_cows.sh
Welcome 'Bulls and Cows' Game
Please input digits of numbers => 3
./bulls_and_cows.sh:Line 39:warning: command substitution: ignored null byte in input
Input 3 numbers of your answer. (1 time) => 345
1 bull and 0 cow.
Input 3 numbers of your answer. (2 time) => 219
1 bull and 0 cow.
Input 3 numbers of your answer. (3 time) => 398
1 bull and 0 cow.
Input 3 numbers of your answer. (4 time) => 470
1 bull and 1 cow.
Input 3 numbers of your answer. (5 time) => 709
1 bull and 0 cow.
Input 3 numbers of your answer. (6 time) => 507
2 bull and 0 cow.
Input 3 numbers of your answer. (7 time) => 504
1 bull and 0 cow.
Input 3 numbers of your answer. (8 time) => 570
1 bull and 1 cow.
Input 3 numbers of your answer. (9 time) => 407
2 bull and 0 cow.
Input 3 numbers of your answer. (10 time) => 307
2 bull and 0 cow.
You failed 10 times...
The answer is '567'

in conclusion

By creating this program

--Variables --Variable manipulation --Conditional expression --Repeating syntax --Function --read command --shuf command

I understand.