bash: spin while process completes in the background

spin.sh

#!/bin/bash

spin() {
	local s=("|" "/" "-" '\x5C')
	local i=0
	while kill -0 $1 2> /dev/null; do
		echo -en "[${s[$i]}]"\\r
		i=$(( $i == 3 ? 0 : $i + 1 ))
		sleep .1
	done
}

## Example usage

# Execute a command in a subshell with output suppressed (maybe piped to file)
(COMMAND > /dev/null 2>&1)&

# wait for it with a spinner
spin $!