If I understand you question correctly, you could attempt a solution where you run ksh from backticks, and have ksh tell you what it's environment is. For example:

{
  my @lines = `/bin/ksh -c ". oraenv -d; set"`;
  for (@lines) {
    next unless /=/;
    my($k,$v) = split /=/, $_, 2;
    $ENV{$k} = $v;
  }
}
[download]

That should call /bin/ksh so it runs the script and then it has /bin/ksh run set, which dumps all the variables of the shell, and the results of the set should then be parsed and inserted into %ENV

I forewarn that that code is untested.