use strict;
use warnings;

use feature 'say';

use File::Copy;
use File::Spec::Functions;
use File::Find::Rule;
use File::Path qw(make_path);
use Cwd;

my $pwd = cwd();
my $dir = catdir($pwd,'source');

my $rule = File::Find::Rule->new;
$rule->file;
$rule->maxdepth(1);
my @files = $rule->in($dir);

foreach my $file (@files) {
	my ($extension) = ($file =~ m/.+\.(.+)/);
	my $subdir = catdir($dir,$extension);
	
	if (!(-d $subdir)) {make_path($subdir);}
	copy($file,$subdir);
}

##</code><code>##

source
     test1.gif
     test1.pdf
     test1.txt
     test2.gif
     test2.pdf
     test2.txt
     test3.gif
     test3.pdf
     test3.txt

##</code><code>##

source
     test1.gif
     test1.pdf
     test1.txt
     test2.gif
     test2.pdf
     test2.txt
     test3.gif
     test3.pdf
     test3.txt
     gif
          test1.gif
          test2.gif
          test3.gif
     pdf
          test1.pdf
          test2.pdf
          test3.pdf
     txt
          test1.txt
          test2.txt
          test3.txt