check if one array is empty in array of arrays

Question

I am writing a perl script which there should be an array of arrays. This array finds all folders in the current directory and then the size of array depends on folders. The children arrays contains all files name which are included. It may I have an empty folder, but still I would like to create an array for that as well.

my $root = "myCurrenDir";
@test = grep { -d "$root/$_" } read_dir($root);
my @array = ? # how can be defined

Let's assume that in the current directory there are two folders. Then the parent array contains two arrays as children. (Maybe one is empty).

Then I want to check if (both of) arrays are empty or not and proceed to do next.

I googled but could not find a clear solution for that. May I ask your help? (maybe it is simple but I stick on!).

So @test now contains only directories, and you want to find all files in $root and put them in @array? — Håkon Hægland
– Håkon Hægland, Commented Mar 3, 2017 at 10:36
when you have the '@test' with list of sub-directories in it. Don't you want to find all files in every item (subdir) in '@test' and add them as an child array in '@array' ? — taiko
– taiko, Commented Mar 3, 2017 at 12:08

Dave Cross · Accepted Answer · 2017-03-03 11:21:43Z

7

Evaluating an array in a scalar context will return the number of elements in the array. We can use that to implement simple logic that checks arrays to see if they contain any data.

if (@array) {
  # @array contains data
} else {
  # @array contains no data
}

If you have an array that contains references to other arrays then we can still use the same logic - we just need to dereference our array reference.

if (@{ $array[0] }) {
  # $array[0] contains data
} else {
  # $array[0] contains no data
}

Of course, we'll probably want to examine @array in a loop to work on all of the child arrays;

for (@array) {
  if (@$_) {
    # child array contains data
  } else {
    # child array contains no data
  }
}

Does that help?

Also, if you're walking directory trees, then File::Find might be an easier approach.

answered Mar 3, 2017 at 11:21

Dave Cross

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1 Comment

Royeh Over a year ago

Thanks a lot for your answer. This was what I want looked for!

taiko · Accepted Answer · 2017-03-03 12:10:35Z

I think this might serve you

use warnings;
use strict;

my @arr_repository;
#declare working directory
my $root = ".";      
opendir ROOT, $root or die "$root:$!";
#creating list of directories in working
my @list_of_dirs=sort (grep (!/^(\.|\.\.)$/ && -d   "$root/$_",readdir(ROOT)));     directory
foreach my $dirName (@list_of_dirs) {
        my @arr_ref_fileList;
        #reading files in directory and inserting them in array_ref
        my $arr_ref_fileList = read_directory($dirName);
        #adding array with filenames into array     
        push @arr_repository, [@$arr_ref_fileList];    
        }

sub read_directory {
    my $input_dir = shift;
    opendir IN,$input_dir or die "$input_dir:$!";
    my @list_of_files=sort (grep (!/^(\.|\.\.)$/ && -f "$input_dir/$_",readdir(IN))); # reading only files, avoiding  "." and ".."
    closedir(IN);
    return \@list_of_files;
    }

you might want to use hash of arrays instead, then you will be able to see what directory contains what files.
```
$hash_repository->{$dirName} = [@$arr_ref_fileList];
```
you might to want to make the script recursive in case the directory being checked contains directories itself.

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