If you _really_ wanted to wipe everything it seems like this would work (and possibly have weird-fun consequences). Of course, its not the Right Thing to do.

foreach $symname (sort keys %main::) {
  local *sym=$main::{$symname};
  if defined $sym {
    undef $sym;
    print "\$$symname was undefined\n";
  }
  if defined @sym {
    undef @sym;
    print "\@$symname was undefined\n";
  }
  if defined %sym {
    undef %sym;
    print "\%$symname was undefined\n";
  }
}
[download]

-Vlad