The first part is just creating 3d arrays "biu(i,j,k)"...

If I understand you correctly the best way to do that is to construct them the same way you change them later.

I've used the perlish for loop and started at 0 (you'll need to correct the assignments at the end to match to avoid any off by 1 errors).

Data::Dumper helps to see what is going on.

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my $u15 = 15;
my $u105 = 105;
my $u25 = 25;

my (@biu);
for my $k (0..11) {
    for my $j (0..25){
        for my $i (0..25){
            $biu[$k][$j][$i] = $u105;
         }
     }
}

my (@zcu);
for my $k (0..11) {
    for my $j (0..25){
        for my $i (0..25){
            $zcu[$k][$j][$i] = $u15;
         }
     }
}

for my $k (0..12) {
    for my $i (0..5) {
        $biu[$i][4][$k] = $u25;
     }
     for my $i (21..25){
         $biu[$i][4][$k] = $u25;
     }
     for my $i (0..4) {
         $biu[$i][22][$k] = $u25;
     }
     for my $i (21..25) {
         $biu[$i][22][$k] = $u25;
     }
#
}

print Dumper \@biu;
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