How could you make a destructive change? Well, the same way that everyone else does it: by versioning. The simplest approach would be to have /bin/bash2, /bin

How could you make a destructive change? Well, the same way that everyone else does it: by versioning. The simplest approach would be to have /bin/bash2, /bin/bash3 etc., with /bin/bash defaulting to the last (current) unversioned bash release. Then when you write a script that depends on a new feature you'd reference #!/bin/bash3 or whatever. More complex schemes are possible but probably not needed here. It's not rocket science. And as your example illustrates: This kind of versioning is actually needed even in the current (almost stale) development-mode of bash. Its absence is the reason why many people still target sh as the lowest common denominator...