#!/usr/bin/perl -w

use strict;

local $\ = "\n";

sub oldsub {
  my $level = shift;
  print "oldsub [$level]";
  oldsub($level - 1) if $level > 0;
}

sub newsub {
  print "newsub [$_[0]]";
}

my $oldsub_ref = \&oldsub;

$oldsub_ref->(2);
print '-' x 10;

*oldsub = \&newsub;

$oldsub_ref->(2);