$string = 'thisIsATest'

(substr( $a = $string, $_, 2)) =~ s/(.)(.)/$2$1/
, print $a . $/ 
    for (0 .. length($string) - 2)

htisIsATest
tihsIsATest
thsiIsATest
thiIssATest
thissIATest
thisIAsTest
thisIsTAest
thisIsAeTst
thisIsATset
thisIsATets