"ABCDEF" =~ /([A-Z]{3})(?{print "$1\n"})(?!)/;

##</code><code>##

ABC
BCD
CDE
DEF
##</code><code>##

"ABCDEF" =~ /(\w{2,}?)(?{print "$1\n"})(?!)/;

##</code><code>##

AB
ABC
ABCD
ABCDE
ABCDEF
BC
BCD
BCDE
BCDEF
CD
CDE
CDEF
DE
DEF
EF