1. Perform a sort of compile-time 'require' *only if* this module hasn't been 'use'-d before. A table of what modules have already been loaded is maintained in some variable that I don't recall at the moment.

2. Call the 'import'-function (I think) *if* it is present in the 'use'-d package. This is performed on every occurence of 'use'. The import function is the one that can optionally export symbol-names (like your constants) to the calling package.

Building your own import function is a hassle, so the easy way is to use the standard Exporter package... The man-page of the Exporter package can explain everything you want to know (and a lot more) about exactly how to use it. For starters, this should do:

--file foo.pm--

package foo;
use Exporter;
@ISA=qw(Exporter);
@EXPORT=qw($const1 $const2 $const3);
# rest of package including constant data
[download]

If you'd use'd the foo package, the same would still work, but you would also have access using $const1 from the calling package.

Hope it helps...