The following bash-function is displaying a spinner as long as data can be read from stdin, for example reading from pipe. In the moment the stdin stream is closed, the spinner will terminate.

Credits: It is a modification of the spinner of http://fitnr.com/showing-a-bash-spinner.html

#!/bin/bash

spinner()
{
  ## hide the cursor
  tput civis

  local spinstr='|/-\'
  printf " [%c] " "$spinstr"
  while read -N 30 chunk; do
     printf "\b\b\b\b\b\b"
     local temp=${spinstr#?}
     local spinstr=$temp${spinstr%"$temp"}
     printf " [%c] " "$spinstr"
  done
  ## overwrite the spinner
  printf "\b\b\b\b\b\b "
  ## return to original cursor position
  printf "\b\b\b\b\b\b"
  ## unhide the cursor
  tput cnorm
}

This spinner can be used to display a progress when performing an untar or  to show activity in syslog file:

tail -f /var/log/syslog | spinner