Re^2: Trouble usig a subroutine from a custom module

I second unbolding your post. It is good that you name disadvantages and vulnerabilities, but bold should be used sparingly.
choroba already commented on several of your points
2: instead of calling it a "module that isn't really a module", you could call it a "snippet", or a "paste".
3c: the execute bit is not relevant in this context (it doesn't prevent reading, that's what read permission is for) The execute bit would allow for a standalone script with shebang to be called directly without explicitly calling perl[.exe]
5: I myself have a snippet that defines π via
```
use constant PI => atan2(0, -1);
[download]
```
(which has other disadvantages)
The non-accessibility of $PI in your case is because it is defined within eval.
reading a complete file was just recently discussed in e.g. Re^3: Entity statistics. (I like Path::Tiny)

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