In case you need to search recursively, you may use the File::Find core module:

use strict;
use warnings;
use File::Find;

# Search current dir unless dir(s) given as command line args
@ARGV = qw(.) unless @ARGV;

find( \&get_dirs_with_numbers, @ARGV );

sub get_dirs_with_numbers {
    return unless /^\d+$/;    # your regex
    print $File::Find::name . "\n";
}
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find function from File::Find scans directories in @ARGV recursively and for each file calls the referenced function (coderef) get_dirs_with_numbers. Before calling your function find by default changes to the directory being scanned and sets the following variables:

• $File::Find::dir -- visited directory path relative to the starting directory
• $_ -- basename of the file being visited
• $File::Find::name -- full path of the file being visited