Text-based tic-tac-toe in bash (continued)

Question

I wrote this two-player tic-tac-toe program in bash. To make a move, you enter a number between 1 and 9 which corresponds to the square:

1|2|3
4|5|6
7|8|9

I originally submitted this code for code review here, and I'm resubmitting it now that I have implemented the changes suggested for it.

This is my new code:

#!/usr/bin/env bash

declare -r BOARD_SIZE=9
declare -r DEFAULT_SQUARE_VALUE=-
declare -ra PLAYERS=(O X)
declare -ra WINNING_COMBINATIONS=("1 2 3" "4 5 6" "7 8 9" "1 4 7" "2 5 8" "3 6 9" "1 5 9" "3 5 7")

print_move_indices() {
    echo "Move indices:"
    echo "1|2|3"
    echo "4|5|6"
    echo "7|8|9"
    echo
}

draw_board() {
    shift
    for i in {1..3}
    do
        echo "$1|$2|$3"
        shift 3
    done
}


get_placement() {
shift
    while true
    do
        echo "Please enter a valid move (1-$BOARD_SIZE)"
        read -r n
        echo

        if [[ "$n" -gt 0 ]] && [[ "$n" -le "$BOARD_SIZE" ]] && [[ "${!n}" == "$DEFAULT_SQUARE_VALUE" ]]
        then
            placement=$n
            return
        fi

    done
}

is_draw() {
    shift
    for square in "$@"
    do
        if [[ "$square" == "$DEFAULT_SQUARE_VALUE" ]]
        then
            return 1
        fi
    done
    return 0
}

is_winner() {
    shift

    for combination in "${WINNING_COMBINATIONS[@]}"
    do
        is_win=1
        first_square="${combination:0:1}"
        for square in $combination
        do
            if [[ "${!square}" == "$DEFAULT_SQUARE_VALUE" ]] || [[ "${!square}" != "${!first_square}" ]]
            then
                is_win=0
                break
            fi
        done

        if [[ $is_win -eq 1 ]]
        then
            return 0
        fi
    done

    return 1

} 

board=( "/" $(for i in $(seq 1 $BOARD_SIZE); do echo "$DEFAULT_SQUARE_VALUE"; done) ) # dummy value at index 0 so that indices start from 1
current_turn="O"

print_move_indices

while true
do
    echo -e "$current_turn's turn\n"

    draw_board "${board[@]}"
    get_placement "${board[@]}"
    board[placement]="$current_turn"

    if is_draw "${board[@]}"
    then
        echo "Draw!"
        echo
        draw_board "${board[@]}"
        exit
    elif is_winner "${board[@]}"
    then
        echo "$current_turn is the winner!"
        draw_board "${board[@]}"
        exit
    fi

    [[ "$current_turn" == "${PLAYERS[0]}" ]] && current_turn=${PLAYERS[1]} || current_turn=${PLAYERS[0]}

    echo -en "\n\n\n"
done

Example game:

Move indices:
1|2|3
4|5|6
7|8|9

O's turn

-|-|-
-|-|-
-|-|-
Please enter a valid move (1-9)
1




X's turn

O|-|-
-|-|-
-|-|-
Please enter a valid move (1-9)
3




O's turn

O|-|X
-|-|-
-|-|-
Please enter a valid move (1-9)
9




X's turn

O|-|X
-|-|-
-|-|O
Please enter a valid move (1-9)
5




O's turn

O|-|X
-|X|-
-|-|O
Please enter a valid move (1-9)
7




X's turn

O|-|X
-|X|-
O|-|O
Please enter a valid move (1-9)
4




O's turn

O|-|X
X|X|-
O|-|O
Please enter a valid move (1-9)
8

O is the winner!
O|-|X
X|X|-
O|O|O

I do not know much about bash, so any feedback would be much appreciated.

Answer 1

It is easy to understand the user prompts when running the code -- and fun, too. Here are some minor suggestions.

---

When you described the game as "two-player", I assumed I would be playing against the computer. You should make it clear that the user is playing both X and O. Add some printed out text to print_move_indices.

---

I would prefer fewer blank lines between turns in the printed output.

---

When I type in a valid number that has already been guessed, I get the message that I need to type in a valid number:

Please enter a valid move (1-9)
1

X's turn

O|-|-
-|-|-
-|-|-
Please enter a valid move (1-9)
1

Please enter a valid move (1-9)
1

Please enter a valid move (1-9)

This is misleading. It would be better to inform the user that the number was already guessed, and that a new number is required.

---

Add indentation in this function. Change:

get_placement() {
shift

to:

get_placement() {
    shift

---

Add space around the .. operator for better readability:

for i in {1 .. 3}

---

The word "draw" has 2 meanings in the code. In the function named is_draw, draw refers to the case where neither player wins. In the function named draw_board, draw refers to printing the board on the output. This is a little confusing. It might be better to rename draw_board as show_board.