#!/usr/bin/perl

use strict;
use warnings;

use File::Find qw( find );

my ($path) = @ARGV
    or die("usage: perl dir_size.pl dirpath\n");

opendir(my $dh, $path)
    or die("Can't open dir $path: $!\n");

while (defined(my $dir = readdir($dh)) {
    next if $dir =~ /^\./;

    my $full_dir = "$path/$subdir";
    next if ! -d $full_dir;

    my $total = 0;
    find(sub { $total += -s if -f $_ }, $full_dir);

    print "The total size of the files in $dir is "
        . sprintf("%.2f Kb", ($total/1024)) . "\n";
    print "The total size of the files in $dir is "
        . sprintf("%.2f Mb", ($total/(1024*1024))) . "\n";
}
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I don't know why people use a named sub for find. If I did want to split out the logic into a separate sub, I'd do something like

sub some_sub {
   my @results;
   find(sub { push @results, $_ if check($_) });
   ...
}

sub check {
   ... Check if the file matches. Doesn't know about File::Find ...
}
[download]