I think that you would be better off looking at the documentation for require rather than using eval. If your first program looks like this.

#! perl -sw
use strict;

require 'test2.pl';

print weather();
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And your second program like this (test2.pl)

#! perl -sw
use strict;

sub weather {
    # do stuff to gen data
    return 'This is the generated data';
}

1;
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When test1.pl is run it gives the following output

C:\test>test
This is the generated data
C:\test>
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