$ perl -e'BEGIN{@ns{keys %::} = ()}; $foo = "bar";@names = grep {!exists $ns{$_}} keys %::; print "@names",$/'
foo names
$ 

##</code><code>##

print "foo has: ", $_, $"
        for (grep {*foo{$_} qw/SCALAR ARRAY HASH CODE GLOB IO/;


##</code><code>##

$ perl -e'BEGIN{@ns{keys %::} = ()}; $foo = "bar";@names = grep {!exists $ns{$_}} keys %::; print ${*foo{SCALAR}} ,$/'
bar
$