Programs not outputting a final newline to stdout leave a prompt that doesn't start on column 0, and readline seams to not takes this into consideration, but still optimizes redraws and overwrites so you get an inconsistent display. This bugs seam to exist in a lot of shells and interactive programs. The program causing the issue isn't POSIX conform though.

> I can’t ever remember seeing a bug in either bash

Shellshock [0] is a rather famous example, but bugs like that are rare enough that they make the news when they're found.

[0] https://en.wikipedia.org/wiki/Shellshock_%28software_bug%29

I had a fun bug where bash would run scripts out of order!

This would lead to impossible states, like

if cat foo | false; then echo hmm; fi

Producing output sometimes, depending on whether or not `cat foo` or `false` return value was used

[0] https://lists.gnu.org/archive/html/bug-bash/2015-06/msg00010...

Depending on how you define "bash" and "bug", funny things happen when you run on a computer with 0 remaining hard drive space.

> Joking aside I can’t ever remember seeing a bug in either bash or zsh, never seen either crash or segfault and anytime I’ve had weirdness it’s always turned out to be me missing something.

Given that this statement begins with "joking aside", I have to assume it is either a meta-joke or an uninformed opinion. Taking the subsequent sentence into account thoroughly reinforces the former.

Well played. :-)

I've been able to trigger a segfault in zsh with certain plugins, a directory with a lot of files/folders, and globs with a bunch of * characters.

Amen.