@$array[$i,$i+1] = @$array[$i+1,$i];

##</code><code>##

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

my $arrayref = ['A','B','C','D'];
print "Before: ", join(' ',@$arrayref), "\n";

@$arrayref[1,2] = @$arrayref[2,1];         # assign into an array slice

print "After : ", join(' ',@$arrayref), "\n";

=output
Before: A B C D
After : A C B D