Hi all! I have been trying to edit the above example in order to create a directory tree that goes: structure/molecule/step. As in, /struct1/AB0001/S00001/ and /struct2/BC0001/S00001/. So, struct1 corresponds only to molecule AB, and struct2 corresponds only to molecule BC. However, both AB and BC files should have the same "steps" subdirectories in them, each time from S00001 to whatever step we are calculating at the time. With that in mind, I figured to first create the "parent" directories struct1 and struct2 and then, in another loop, to put in the relevant subdirectories. This however gives me the error "Use of uninitialized value $structs in concatenation (.) or string".

#/bin/perl/

use strict;
use warnings;
use File::Path qw(make_path);

my @structs;
my $structs;

my @molecs;
my $molecs;

my @steps;
my $steps;

# Parent structure directory.

@structs = (
    dir_tree( 'struct', 7, 1, 1),
    dir_tree( 'struct', 7, 2, 2 ),
   # dir_tree( 'struct', 7, 3, 3 ),
   # dir_tree( 'struct', 7, 4, 4 ),
   # dir_tree( 'struct', 7, 5, 5 ),
   # dir_tree( 'struct', 7, 6, 6 ),
);

# Subfolder molecule directory.

@molecs = (
    dir_tree( 'AB', 6, 1, 1 ),
    dir_tree( 'BC', 6, 1, 1 ),
   # dir_tree( 'XZ', 6, 1, 4 ),
   # dir_tree( 'XY', 6, 1, 4 ),
   # dir_tree( 'QU', 6, 1, 4 ),
   # dir_tree( 'QE', 6, 1, 4 ),
);

# Subfolder steps directory.

@steps = (
   dir_tree( 'S', 6, 1, 2 ),
);


for $structs (@structs) {
    make_path "/media/RAIDstorage/home/results/$structs";
}


for $molecs (@molecs) {
        for $steps (@steps) {
        make_path "/media/RAIDstorage/home/results/$structs/$molecs/$s
+teps";
        } 
    }

# Define subroutine here.
sub dir_tree {
    my ( $name, $total_length, $from, $to ) = @_;

    my $length = $total_length - length($name);
    my $format = "${name}%0${length}d";

    return map sprintf( $format, $_ ), $from .. $to;
}
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If I use an integrated loop, like so

for $structs (@structs) {
    for $molecs (@molecs) {
        for $steps (@steps) {
        make_path "/media/RAIDstorage/home/results/$structs/$molecs/$s
+teps";
        } 
    }
}
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I get no errors but the wrong directory tree. That way, all $molecs are added in both $structs, when I want AB to go only in $struct1 and BC to go only in $struct2. I also tried using two different subroutines, like sub1 and sub2, but it also gave me the same error, "uninitialized value". Is the answer the two different subroutines, only I did it wrong? Any hints as to what I'm messing up? Thank you all!