Only scripts that are sourced by the active shell Edit: to clarify, any shell script that is executed will define its own shell to execute with (the #! line).

Only scripts that are sourced by the active shell Edit: to clarify, any shell script that is executed will define its own shell to execute with (the #! line). There may be some issues if scripts have declared their shell as /bin/sh but they use bashisms, and then /bin/sh isn't provided by bash anymore, but honestly that's not necessarily related. The discussion here is about changing the default login shell for interactive user accounts to fish. If they did this though, it would be nice if they would use dash for /bin/sh, but I'm not sure how that's licenced - possibly gpl3 too?