Conway's Game of Life in POSIX Shell

CGoL.sh

#!/bin/sh

xs=80 ys=24
ORIGIN=$(clear) LF='
'

if [ ! ${RANDOM} ]; then
  set -- $(head -c $((xs * ys)) /dev/random | od -An -vtu1)
fi

j=0; while [ $j != $ys ]; do
  i=0; while [ $i != $xs ]; do
    if [ ${RANDOM} ]; then
        r=${RANDOM}
    else
        r=$1
        shift
    fi
    export cx${i}y${j}=$((r%2))
    i=$((i+1))
  done
  j=$((j+1))
done

clear
while true; do
  buf=$ORIGIN
  j=0; while [ $j != $ys ]; do
    i=0; while [ $i != $xs ]; do
      case $((cx${i}y${j})) in
        1) buf="$buf*" ;;
        *) buf="$buf " ;;
      esac
      i=$((i+1))
    done
    buf="$buf$LF"
    j=$((j+1))
  done
  echo "${buf%$LF}"

  j=0; while [ $j != $ys ]; do
    i=0; while [ $i != $xs ]; do
      t=0
      for l in -1 0 1; do
        for k in -1 0 1; do
          tx=$(((i+k+xs)%xs)) ty=$(((j+l+ys)%ys))
          t=$((t+$((cx${tx}y${ty}))))
        done
      done; t=$((t-cx${i}y${j}))
      case $((cx${i}y${j})) in
        1) case $t in 2|3) export cnx${i}y${j}=1 ;;
                        *) export cnx${i}y${j}=0 ;;
           esac ;;
        *) case $t in   3) export cnx${i}y${j}=1 ;;
                        *) export cnx${i}y${j}=0 ;;
           esac ;;
      esac
      i=$((i+1))
    done
    j=$((j+1))
  done

  j=0; while [ $j != $ys ]; do
    i=0; while [ $i != $xs ]; do
      export cx${i}y${j}=$((cnx${i}y${j}))
      i=$((i+1))
    done
    j=$((j+1))
  done
done