The key thing with exec is that it replaces your process

Yes, I guess you can't do that with babashka, but ProcessBuilder + inheritIO + System/exit the exit code of that process is the closest thing that comes next probably

I believe this will be hard to do in a portable way, won't it? bash relies on system call https://linux.die.net/man/3/execv to perform the trick. How would that work in Windows?

ProcessBuilder fulfils this role well enough functionally, although it's not technically the same. So I think we don't need anything new.

I've been playing with babashka, and one initial puzzle for me was the printing behaviour

% bb '(:a {:a 3})'
3
% bb '(:b {:a 3})'
%

so a final nil value doesnt seem to be printed

@grahamcarlyle nil is not printed. This is because lots of side effects return nil, e.g. (println :foo) and a lot of scripts end in something side-effecting

So if you really want to print the nil, you can use (prn ..) instead

yeah it makes sense, but i didnt realise this behaviour initially and so was puzzled by the absence or presence of output

I guess it's not properly documented.

Feel free to make a documentation PR if you wish so

is there a way of controlling the input/output processing behaviour of bb within a script? so the things that the -o/-O flags would change, i wondered if there was a function i could call to alter the behaviour. My use was a script that in some cases wanted to output text and in other cases EDN.

In that case I think it's better to just use println and prn. The flags are mostly there for one-liners.

i guess another utility of being able to set the flags in a script is when a script could be called via shebang style or as a script

as the flags would be in 1 place

Script from work where we start 2 clojure processes (for building CLJS and less) and 1 boot process (for a JVM Clojure process / REPL) using 1 babashka script: https://gist.github.com/borkdude/8f5dff7c2330ca520403eb44c9013a83. The alternative was to have 3 different tabs open