use strict;
use warnings;
use 5.010;

my $len    = 4;
my $string = "01234abc";

for (0 .. (length $string - $len) ) {
    say substr $string, $_, $len;
}

# or in an array
my @chunks = map {substr $string, $_, $len} (0 .. (length $string - $len) );
say join "<>", @chunks;