print "'$1' found at ", pos( $s ) - 4 
    while $s =~ m[(?<=^.{4})*?(....)]g;

'the ' found at  0
'quic' found at  4
'k br' found at  8
'own ' found at  12
'fox ' found at  16
'jump' found at  20
's ov' found at  24
'er t' found at  28
'he l' found at  32
'azy ' found at  36