Bash script to print a subset of array

arraybyindex.sh

#!/bin/bash

# Usage:
# arraybyindex.sh <uint array> <index> <length>
# arraybyindex.sh '[1,2,3,4,5,6,7,8]' 4 2
# Output:
# 5 6
# - or -
# arraybyindex.sh '[1,2,3]' 1 1
# 2

isuint() { [[ $1 =~ ^[0-9]+$ ]] ;}

if [ $# -lt 2 ]; then
  echo "Expecting two or three arguments that is list of uint8 numbers and index and length, like ${0} '[1,2,3]' 1 2"
  exit 2
fi

ARR="$1"

if ! isuint "$2" ; then
  echo "Expecting the second argument being a number but it's '$2'"
  exit 3
fi

if [ $# -gt 2 ] &&  ! isuint "$3"; then
  echo "Expecting the third argument being a number but it's '$3'"
  exit 4
fi

INDEX="$2"
[ $# -gt 2 ] && SIZE="$3" || SIZE=""

ARR_CONVERTED=`echo $ARR | sed 's/[,]/ /g' | sed 's/\[\|\]/ /g'`
ARR_BASH=( $ARR_CONVERTED )

if [ 'x' == "x$SIZE" ]; then
  OUT_ARRAY="${ARR_BASH[@]:INDEX}"
else
  OUT_ARRAY="${ARR_BASH[@]:INDEX:SIZE}"
fi

OUT=`echo "[${OUT_ARRAY[@]}]" | sed 's/ /,/g'`
echo "$OUT"
[ -x "$(command -v xsel)" ] && echo -n "$OUT" | xsel -ib