#
#                    1         2         3
#          01234567890123456789012345678901234
my $seq = "LPNTGVTNNAYMPLLGIIGLVTSFSLLGLXKARKD";

#
# Note that substr counts offsets from zero so adjust
# if you are counting from one.

my $start = 5;
my $end = 10;
my $length = $end - $start + 1;

my $cut = substr $seq, $start, $length;
print "$cut\n";