tictactoe.sh

#!/usr/bin/env bash
# tictactoe.sh - tictactoe in bash for fun
#

set -eu

board="         "
turn="X"

print_board() {
    tput smul
    echo "0|${board:0:1}|${board:1:1}|${board:2:1}"
    echo "1|${board:3:1}|${board:4:1}|${board:5:1}"
    echo "2|${board:6:1}|${board:7:1}|${board:8:1}"
    tput rmul
    echo " |0|1|2"
    echo
}

read_digit() {
    name="$1"
    while true; do
        printf '%s> ' "$name" >&2
        read -r
        if printf "%s" "$REPLY" | grep -qE "^[012]$"; then
            break
        else
            echo "Invalid input" >&2
        fi
    done
    echo "$REPLY"
}

updated_board() {
    sym="$1"
    pos="$2"
    next=$((pos + 1))
    echo "${board:0:$pos}${sym}${board:$next:9}"
}

check_win() {
    s="$1" #symbol

    # keep regex simpler - turn board into string of numbers for matching symbol
    symstr=$(printf "%s" "$board" | fold -w1 | nl | grep "$s" | tr -d '\n')

    printf "%s" "$symstr" | grep -q "1.*2.*3\|\
4.*5.*6\|\
7.*8.*9\|\
1.*4.*7\|\
2.*5.*8\|\
3.*6.*9\|\
1.*5.*9\|\
3.*5.*7"
}


while true; do
    print_board

    while true; do
        echo "*** player $turn ***"
        row=$(read_digit "row")
        col=$(read_digit "col")
        pos=$((row * 3 + col))

        if [ "${board:pos:1}" != " " ]; then
            echo "Position is not empty" >&2
        else
            break
        fi
    done

    board=$(updated_board "$turn" "$pos")

    echo

    if check_win $turn; then
        echo "*** player $turn wins ***"
        break
    fi

    if [ $turn = "X" ]; then
        turn="O"
    else
        turn="X"
    fi

done

Sample Run

sh-3.2$ ./tictactoe.sh
0| | |
1| | |
2| | |
 |0|1|2

*** player X ***
row> 2
col> 1

0| | |
1| | |
2| |X|
 |0|1|2

*** player O ***
row> 1
col> 1

0| | |
1| |O|
2| |X|
 |0|1|2

*** player X ***
row> 2
col>
Invalid input
col> 0

0| | |
1| |O|
2|X|X|
 |0|1|2

*** player O ***
row> 1
col> 0

0| | |
1|O|O|
2|X|X|
 |0|1|2

*** player X ***
row> 2
col> 2

*** player X wins ***