#!/usr/bin/perl -lw
use strict;

my $a = 1;
my $b = 2;

sub swap {
  my @in = \( @_ ); # create our references, although pointless here
  ${$in[0]}^=${$in[1]};${$in[1]}^=${$in[0]};${$in[0]}^=${$in[1]};
}

print "$a $b";
swap($a,$b);
print "$a $b";
__DATA__
output:
1 2
2 1