How to load module not in INC in Perl during runtime?

Question

How do I load a module with a path not in the @INC in Perl?

I've read the answers on how to add a path to the @INC, but the issue is that @INC has to be changed at the beginning of the code. After it's compiled, all the modules I've come across look to @INC to find the location of the module. My issue is that we're trying to separate out all these environment specific things to a config file. If it's in a config file, the path needs to be read before it can be pushed to @INC, but then the code has already been compiled and it seems @INC can't be modified.

1. Is there a way? Is there a library that lets me load a module and pass it a custom path?
2. Is this a terrible bad thing to do? Why?

Answer 1

Perl has an incremental compilation model which means that code can be executed before other code is even parsed. For this, we can use phase blocks (aka. phasers):

BEGIN {
    print "This is executed as soon as the block has been parsed\n";
}

Such a phase block could also be used to load a configuration file.

For example, use statements are effectively syntactic sugar for a BEGIN block.

use Foo::Bar qw/baz qux/;

is equivalent to

BEGIN {
    require Foo::Bar; # or: require "Foo/Bar.pm";
    Foo::Bar->import(qw/baz qux/);
}

We can also load modules at runtime, although that's only sensible for object-oriented modules.

So we have three options:

1. Load config in the BEGIN phase and add the correct library paths before loading the actual modules
2. Load the modules manually during BEGIN with their full path (e.g. require "/my/modules/Foo/Bar.pm"
3. Figure out the configuration at runtime, load modules after that.

Using bare require is fairly uncomfortable, which is why Module::Runtime exists