sub traditional {
    my $C = $A;
    $A = $B;
    $B = $C;
}

sub non_trad {
    ($B, $A) = ($A, $B);
}

Global symbol "$A" requires explicit package name at ./bench.perl line 12.
Global symbol "$B" requires explicit package name at ./bench.perl line 13.

##</code><code>##

#!/usr/bin/perl -w

use vars qw/$A $B @Arr/;

use strict;
use Benchmark;

$A = rand(10);
$B = rand(10);
@Arr = ($A, $B);

sub traditional {
    my $C = $A;
    $A = $B;
    $B = $C;
}

sub non_trad {
    ($B, $A) = ($A, $B);
}

sub array_slice1 {
    @Arr = @Arr[1,0];
}

sub array_slice2 {
    @Arr[1,0] = @Arr;
}

timethese (100000, {
    "traditional" => \&traditional,
    "not traditional" => \&non_trad,
    "array1" => \&array_slice1,
    "array2" => \&array_slice2,
});

Results:
Benchmark: timing 100000 iterations of array1, array2, not traditional, traditional...
    	 array1:  4 wallclock secs ( 3.98 usr +  0.00 sys =  3.98 CPU)
    	 array2:  3 wallclock secs ( 3.27 usr +  0.00 sys =  3.27 CPU)
not traditional:  2 wallclock secs ( 2.72 usr +  0.00 sys =  2.72 CPU)
    traditional:  2 wallclock secs ( 1.81 usr +  0.00 sys =  1.81 CPU)