How to create a rotation animation using shell script?

Use that script:

#!/bin/bash

chars="/-\|"

while :; do
  for (( i=0; i<${#chars}; i++ )); do
    sleep 0.5
    echo -en "${chars:$i:1}" "\r"
  done
done

The while loop runs infinite. The for loop runs trough each character of the string given in $chars. echo prints the character, with a carriage return \r, but without linebreak -n. -e forces echo to interpret escape sequences such as \r. There's a delay of 0.5 seconds between each change.

Here's an example using \b, which tells the terminal emulator to move the cursor one column to the left, in order to keep overwriting the same character over and over.

#!/usr/bin/env bash

spinner() {
    local i sp n
    sp='/-\|'
    n=${#sp}
    printf ' '
    while sleep 0.1; do
        printf "%s\b" "${sp:i++%n:1}"
    done
}

printf 'Doing important work '
spinner &

sleep 10  # sleeping for 10 seconds is important work

kill "$!" # kill the spinner
printf '\n'

See BashFAQ 34 for more.