Nested for loop in perl - perl

Question

I'm trying to make a little script with a nested "for" loop in perl.
As I'm learning, at first I've done 3 for loops and it worked well. In order to make something more intelligent, I'd like to nested them but I don't know what is wrong.
If my input text is ABCDEFGHI
I'd like to obtain
text 1 ABC DEF GHI
text 2 BCD EFG HI
text 3 CDE FGH I
But instead of it, my output is
text1 ABC DEF GHI ABC DEF GHI ABC DEF GHI ABC DEF GHI ABC DEF GHI ABC DEF GHI ABC DEF GHI ABC DEF GHI ABC DEF GHI
text2 BCD EFG HI BCD EFG HI BCD EFG HI
text3 CDE FGH I
Here is my script. I'm using perl 5.18.1.
use Modern::Perl '2013';
my #text1;
my #text2;
my #text3;
my $entry = shift;
my $len = length $entry;
for (my $i = 2; $i < $len; $i += 3) {
for (my $i = 1; $i < $len; $i += 3) {
for (my $i = 0; $i < $len; $i += 3) {
my $text = substr($entry, $i, 3);
push #text1, uc($text);
}
my $text = substr($entry, $i, 3);
push #text2, uc($text);
}
my $text = substr($entry, $i, 3);
push #text3, uc($text);
}
say "text1 #text1";
say "text2 #text2";
say "text3 #text3";
I've already taken a look around and here http://perldoc.perl.org/perlsyn.html#For-Loops
Thank you for any help

Answer 1

I don't know why you'd want three nested loops (not counting substr). You only need two: One loop to determine the starting position, and one to walk through the string.
my $text = uc('ABCDEFGHI');
for my $offset (0..2) {
my #parts;
for (my $i=$offset; $i<length($text); $i+=3) {
push #parts, substr($work, $i, 3);
}
say "#parts";
}
Or without substr. to truly demonstrate there are really only two loops:
my $text = uc('ABCDEFGHI');
my #text = split //, $text;
for my $offset (0..2) {
my #parts;
for my $i ($offset..$#text) {
$parts[ ($i - $offset) / 3 ] .= $text[$i];
}
say "#parts";
}
Personally, I'd use
my $text = uc('ABCDEFGHI');
for (1..3) {
my #parts = $text =~ /\G.{1,3}/sg;
say "#parts";
$text =~ s/^.//s;
}

Answer 2

Your three loops do not need to be nested to get your desired output:
use Modern::Perl '2013';
my #text1;
my #text2;
my #text3;
my $entry = shift;
my $len = length $entry;
for (my $i = 0; $i < $len; $i += 3) {
my $text = substr($entry, $i, 3);
push #text1, uc($text);
}
for (my $i = 1; $i < $len; $i += 3) {
my $text = substr($entry, $i, 3);
push #text2, uc($text);
}
for (my $i = 2; $i < $len; $i += 3) {
my $text = substr($entry, $i, 3);
push #text3, uc($text);
}
say "text1 #text1";
say "text2 #text2";
say "text3 #text3";
You could also re-factor this a little, using two nested loops:
use Modern::Perl '2013';
my #texts = ( [], [], [] );
my $entry = shift;
my $len = length $entry;
for ( my $start = 0; $start < 3; $start++ ) {
for ( my $i = $start; $i < $len; $i += 3 ) {
my $text = substr($entry, $i, 3);
push #{$texts[$start]}, uc($text);
}
}
for ( my $start = 0; $start < 3; $start++ ) {
say "text${start} #{$texts[$start]}";
}
As an aside: If you do nest for loops, it will be easier to read and understand your code if you use a different variable as the iterator. The three $i variables you have will work, but I had to check quite a while to make sure that wasn't your problem.