#!/usr/bin/perl
use strict;
use warnings;

our $x = 3;

foo(7);

sub foo {
  my $oldx=$x;
  local $x = shift;
  print "localised x = $x\n";
  print "      old x = $oldx\n";
  foo(0) if $x; # recursive call, only 1 time
}

__END__
localised x = 7
      old x = 3
localised x = 0
      old x = 7