ABashSubShellPitfall.sh

#!/bin/bash

# bash executes this incorrectly.
# On the other hand zsh executes this correctly.
# Because bash spawns a sub-shell inside while-do loop meanwhile zsh doesn't it.
declare -i sum
seq 0 10 | while read num ; do
  let sum+=$num
done

# bash => nothing
# zsh => 55
echo $sum