Hello, Here is my suggestions..

$string = "thisisatest";
@a=split //,$string;
foreach (0..(@a-2))
{
    ($a[$_],$a[$_+1])=($a[$_+1],$a[$_]);
    print @a."\n";
    ($a[$_],$a[$_+1])=($a[$_+1],$a[$_]);
}
[download]

Ciao, Gregor (Edit: forgot newline)