use strict;
use warnings;

my $str = do {local $/; <DATA>};
$str =~ s/\s+//g;
my $len = length $str;

for (my $width = 5; $width; --$width) {
  for (0..($len - $width)) {
    print substr ($str, $_, $width) . "\n";
  }
}

__DATA__
ABCDEFGHIJK
[download]

ABCDE
BCDEF
CDEFG
DEFGH
EFGHI
FGHIJ
GHIJK
ABCD
BCDE
CDEF
DEFG
EFGH
FGHI
GHIJ
HIJK
ABC
BCD
CDE
DEF
EFG
FGH
GHI
HIJ
IJK
AB
BC
CD
DE
EF
FG
GH
HI
IJ
JK
A
B
C
D
E
F
G
H
I
J
K
[download]