No:

require $pathtool;
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is exactly the same as

require "File::Path";
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which fails. Your other attempt,

eval "require $pathtool";
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evaluates the string, which then looks like

require File::Path;
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which succeeds. Consider using the following code if you want a dynamic module loader:

sub require_package {
    for (@_) {
        (my $file = $_) =~ s-::|'-/-g;
        require "$file.pm";
    };
};
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Other alternatives which I recommend against are UNIVERSAL::require and Module::Load because they both hide fatal errors from you, for example compilation errors in the required modules.

Maybe you might want Module::Pluggable for a plugin system.