ex_bash_raindrops/raindrops.sh

#!/usr/bin/env bash

[[ -z $1 || ! $1 =~ ^[0-9]+$ ]] && echo "Usage: $0 <number>" && exit 1
[[ $(( $1%7 )) = 0 ]] && res+="Pling"
[[ $(( $1%5 )) = 0 ]] && res+="Plang"
[[ $(( $1%3 )) = 0 ]] && res+="Plong"
[[ -z $res ]] && res=$1
echo $res