Our standard habit on our OpenBSD machines is to use their packaged version of Bash as the root shell, instead of the default of OpenBSD's version of ksh. When I set up an OpenBSD 6.9 machine recently and started to paste in install steps from our standard instructions, an odd thing happened: the line I'd just pasted in was highlighted in reverse video and Bash just sat there, instead of doing anything. After some fiddling around, I discovered that I had to hit Return in order get things to go (and at that point Bash would act on all of the input without further prompts, even if I'd pasted in multiple lines).

People who are more familiar with Bash and readline than I was already know what this is; this is the Bash readline setting of enable-bracketed-paste. OpenBSD 6.9 is the first Unix I've encountered where this was turned on by default. This isn't because OpenBSD did anything special; instead, it's because OpenBSD 6.9 is the first Unix I've used that has Bash 5.1. As mentioned in the detailed Bash list of changes, bracketed paste mode was enabled by default starting in bash-5.1-alpha. The reverse video behavior of it is also new there; in 5.0 and before, nothing special shows in bracketed paste mode to signal that something unusual is going on.

Bash 5.1 will be rolling out over time to more Unixes, so I suspect that more people will be running into this behavior unless their particular Unix opts to disable it in one way or another. If I had updated to Fedora 34 by now, it's possible I'd have already encountered this (I believe that Fedora 34 has Bash 5.1, but I don't know how Fedora opted to set bracketed paste).

This change to the default of bracketed paste is also in GNU Readline 8.1 (according to its CHANGES). However, Readline has a configuration time option that can change this, so different Unixes may opt to build Readline differently. On a Unix with Readline 8.1+ and bracketed paste enabled by default, I believe that all programs using GNU Readline will automatically have this behavior.

(This directly affects me because these days I build my alternate shell using GNU Readline. If I do nothing, it will someday inherit this behavior on new versions of Fedora and Ubuntu.)

If you decide that you don't want bracketed paste mode, the safest change is to set this in either your $HOME/.inputrc or globally in /etc/inputrc. You would do this with:

set enable-bracketed-paste off

This will (or should) cover Bash and anything else that starts using Readline 8.1 on a Unix that builds 8.1 with this enabled. Adding this to your .inputrc today is harmless if you have Readline 7.0 and Bash 4.4 or later (the versions where this setting was introduced).

If you just want to turn this off only in Bash (at least for now), I think that you want to set up a $HOME/.bashrc that has in it:

bind 'set enable-bracketed-paste off'

You can set this in your .profile, but then it won't be turned on in subshells.

How to set this bind up globally for Bash depends on how your Unix's version of Bash was built and may not be possible. Ubuntu builds Bash so that there's a global /etc/bash.bashrc you can put this bind into, but Fedora and OpenBSD don't. Fedora provides a starting .bashrc for new accounts that source /etc/bashrc, so you can put the bind there and probably get most people. Since Bash is an add-on in OpenBSD, it has nothing like this and people are on their own to disable it one by one.