Re: Incorrect alias expansion within command substitution

[Martijn Dekker]

Op 01-02-22 om 15:23 schreef Chet Ramey:
> Historically, bash (and ksh93) has favored the former. Just about all the
> other shells claiming some sort of POSIX conformance favor the latter (all
> the ash-based shells, yash, mksh).
>
> What are your plans here?

I've no current plans. Any remotely plausible use of aliases is not 
going to be affected either way. I've done some pretty innovative stuff 
in modernish that involves aliases and that too would be unaffected. In 
my view, this difference is relevant to standards and regression test 
writers and probably no one else.

Having said that, I've never understood why ksh stores command 
substitutions as unparsed source code (including comments and all) in 
the parse tree and only parses that at execution time -- including in 
dot scripts (which are otherwise parsed in their entirety before 
execution) and shcomp bytecode output. That seems bizarre. It doesn't do 
that for regular subshells in parentheses or for process substitutions.

And ksh *still* has $(command substitution) parsing bugs -- a currently 
known one is https://github.com/ksh93/ksh/issues/269 and there are 
probably more yet to be discovered.

So, in a hypothetical future where I will finally have managed to 
understand the uncommented and undocumented dark magic that is the ksh 
parser, lexer, expansion and command substitution code, I would like to 
delete the lexer code that skips over a $(comsub) and instead parse 
comsubs the same way as regular subshells or process substitutions. 
Aliases would then be handled the same way as well.

Don't hold your breath though. The chances of it happening sometime this 
decade are low. Plus, there is still a lot of lower hanging fruit to 
pick in this incredibly buggy code base.

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