Re: looping over variables & exporting them at the same time ?

[Greg Wooledge]

On Sun, Jan 28, 2024 at 11:43:49PM -0500, Zachary Santer wrote:
> Why do
> IFS=' ' read -ra list <<< "${!v}"
> instead of
> list=( ${!v} )

The second form does word splitting using the default IFS, so you would
want to change that.  This leaves IFS in an altered state (you can't
temporarily assign it for this command only, because it's an assignment),
unless the assignment is done inside a function where IFS is local.

It also does globbing (filename expansion), which you would need to
suppress.  Once again, this leaves the shell in an altered state, unless
you use "local -" inside a function to localize the -f/+f setting.
That in turn would bump up the required bash version to 4.4.

But, really?  The main reason you don't do x=( $y ) is because it's got
an unquoted expansion just waiting to cause *untold* amounts of trouble.
Even if you think you've covered all your bases, who knows what strange
behaviors or shell bugs are just waiting to leap out and bite you.

> And nameref variables could simplify what you're doing as well.

That's fair, although it does bump up the required bash version to 4.3.

> I'm curious if the guy's actual use-case is even really a list, or if
> that's being extrapolated out of the example he made of what he wanted to
> be able to do. If these things are lists, they should live and die as
> arrays, but then you can't export them.

It's impossible to be sure, of course.  I'm guessing this is part of
some kind of autobuilder ("continuous integration") setup.  This guess
is based on past questions I've seen, rather than the current question
alone.  These "CI" thingamabobs tend to abuse environment variables to
pass all kinds of crap around, and they use rickety shell scripts to
try to control it all.

I'm still concerned about the variable names being used.  I still have a
deeply skeptical belief that there isn't a known, finite set of variable
names to be iterated over.  I'm expecting the next iteration of the
question to be "I lied, and the variables are all of the form XYZ_* and
I have to change all of them, and I won't know in advance what they are".

Or worse still, "I have to use /bin/sh, not bash".