Re: increment & decrement error when variable is 0

[Greg Wooledge]

On Mon, Nov 23, 2020 at 07:36:29PM +0000, Jetzer, Bill wrote:
>                 The prefix and postfix versions of the increment (++) and 
> decrement (--) operators return a non-zero exist status when the varable's 
> value is zero.  This causes scripts to terminate if `set -e` is used

https://mywiki.wooledge.org/BashFAQ/105

Exercises 1 and 2 apply directly.  Everything else on the page applies
too, more broadly.  You may need to read it several times to start to
undo the damage you've already suffered.