It's fragile and opens the door to many hard to debug potential problems.

Though most people were interpreting your intention as trying to use $$symbolic dereference. That's why I asked for more context.

Using hashes for optional values is a common pattern.

> I often put together pieces of code from various places.

Well, the common pattern for that class of problems is to use modules with stable APIs.

If you really want to do code generation by composing code chunks, then consider using package declarations and inspecting an our $scale variable in the STASH

use strict;
use warnings;

package Chunk;

#our $scale =42;

package main;


my $myscale = $Chunk::{scale} // 1;

print $myscale;
[download]

but now that you use packages you're only one step away of using modules ...

HTH! :)