#!/bin/bash
digits=(1 2 3 4);
 for i in ${#digits[@]}; do
   for j in ${#digits[@]}; do
     for k in ${#digits[@]}; do
     echo "$(( ${digits[i]} + ${digits[j]} + ${digits[k]} )) = ${digits[i]} + ${digits[j]} + ${digits[k]}";
      done; done; done | sort -n