Your question is a bit sketchy on the details of what you doing. In particular, what you mean by showing up where it's not supposed to, but I think that you might be able to use package scoping to achieve you aim.

package foo_name_space;
eval "require './data_to_import.dat'";  
package main; ## or your module name
$self->{imported_data} = $foo_name_space::data unless $@; 
}
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I think that would get you part way to your goal at least. Any vars created would be in the 'other' package space, and so isolated from your code.

This would probably work well if any vars created were overwritten with the new data each time the code was invoked, but if new variables are created each time, then the old ones would persist and you would have a memory leak which wouldn't bode well in a mod_perl environment.