my $saved = $_;
$_ = undef;
...
$_ = $saved; 

##</code><code>##

my $tmp;
my $old = \$_;
*_ = \$tmp;
...
*_ = \$old;

##</code><code>##

$ perl -le '$x = 1; $r = \$x; local $x=2; print "$$r $x"'
1 2
$