Error msg should be corrected for NUMBER_BACKUPS variable

if ! [[ $NUMBER_BACKUPS =~ $REcheck ]] ; then
echo "ERROR: NUMBER_BACKUPS not a number" >&2; exit 1
fi
if [ $NUMBER_BACKUPS -lt 0 ] || [ $NUMBER_BACKUPS -gt 20 ]; then
echo "ERROR: NUMBER_BACKUPS must be an integer between 1 and 100 (value: $NUMBER_BACKUPS)" >&2
exit 1
fi

msg should be like

""ERROR: NUMBER_BACKUPS must be an integer between 1 and 20"