How to expand PS1?

Question

I have a shell script that runs the same command in several directories (fgit). For each directory, I would like it to show the current prompt + the command which will be ru

Answer 1

I like the idea of fixing Bash to make it better, and I appreciate paxdiablo's verbose answer on how to patch Bash. I'll have a go sometime.

However, without patching Bash source-code, I have a one-liner hack that is both portable and doesn't duplicate functionality, because the workaround uses only Bash and its builtins.

x="$(PS1=\"$PS1\" echo -n | bash --norc -i 2>&1)"; echo "'${x%exit}'"

Note that there's something strange going on with tty's and stdio seeing as this also works:

x="$(PS1=\"$PS1\" echo -n | bash --norc -i 2>&1 > /dev/null)"; echo "'${x%exit}'"

So although I don't understand what's going on with the stdio here, my hack is working for me on Bash 4.2, NixOS GNU/Linux. Patching the Bash source-code is definitely a more elegant solution, and it should be pretty easy and safe to do now that I'm using Nix.