This post relates to a previous one here : utf8 in directory and filenames
in which I was relating an issue with handling utf8 directory entries. Thanks to Juerd and others for their previous inputs. Hopefully, this post is more to the point.

This is not really a problem anymore, maybe more of a curiosity. But I think it highlights at least a "sneaky" issue with the way Perl internally handles string "upgrades" to utf-8, and at worst maybe a bug. To see the case, please download and run the following program. Running it in any empty directory makes it clearer to follow.
I guess you also need Perl 5.8.1 minimum.

The program creates 2 (empty) files named "Presentación.txt", once using the default encoding of your system (assumed to be iso-8859-1), and once using a utf-8 encoding. You can see the difference between the 2 entries by doing an "ls" at the end of the run.
After creating the files, the program reads the directory via opendir() and readdir(), and scans the entries to count the files. It does this twice and compares the results. The curiosity is that, although the directory path is provided with the same content in both cases (.), the results are different.
There is of course a good reason for that, but it is somewhat counter-intuitive if one looks at the screen output.

#!/usr/bin/perl
use strict;
use warnings;
use Encode;

# Assume the initial default encoding is iso-8859-1
# We leave STDOUT to the standard encoding too, because we presume it 
+corresponds
# to your locale and terminal emulation settings

my $fname_iso = "Presentación.txt"; # fname_iso is bytes
print "  creating file1 [$fname_iso] " . (Encode::is_utf8($fname_iso) 
+? "(utf8)" : "(bytes)") . "\n";
open(F1,'>',$fname_iso) or die "cannot open F1 : $!";
close F1;

my $fname_utf8 = decode('iso-8859-1',$fname_iso); # fname_utf8 is utf8
+ and utf8-marked
# the "o acute" should now be 2 bytes
print "  creating file2 [$fname_utf8] " . (Encode::is_utf8($fname_utf8
+) ? "(utf8)" : "(bytes)") . "\n";
open(F2,'>',$fname_utf8) or die "cannot open F2 : $!";
close F2;

my $numfiles;

    my $dir_iso = "."; # iso bytes by default
    print "testing with path [$dir_iso] " . (Encode::is_utf8($dir_iso)
+ ? "(utf8)" : "(bytes)") . "\n";
    $numfiles = dirread($dir_iso);
    print "result : $numfiles files found\n";

    my $dir_utf = decode('iso-8859-1',$dir_iso); # force internal utf8
    print "testing with path [$dir_utf] " . (Encode::is_utf8($dir_utf)
+ ? "(utf8)" : "(bytes)") . "\n";
    $numfiles = dirread($dir_utf);
    print "result : $numfiles files found\n";

    exit 0;

sub dirread {
    my $path = shift;
    my $fullpath;
    my $numfiles = 0;
    opendir(DIR,$path);
    my @entries = readdir DIR;
    close DIR;
    foreach (@entries) {
        next if $_ =~ /^\./;
        next if $_ =~ /\.pl$/; # skip myself too
        print "dirread() : checking entry [$_] " . (Encode::is_utf8($_
+) ? "(utf8)" : "(bytes)") . "\n"; # should always be 'bytes'
        $fullpath = $path . '/' . $_ ;
        print "dirread() : full path is [$fullpath] " . (Encode::is_ut
+f8($fullpath) ? "(utf8)" : "(bytes)") . "\n";
        if (-f $fullpath) {
            #print "    passes the -f test,";
            unless (open(F1,'<',$fullpath) ) {
                #print "  but cannot be opened : $!\n";
            } else {
                print "   ... passes !\n";
                close F1;
                $numfiles++;
            }
        } else {
            print "    ... fails the -f test !\n";
            unless (open(F1,'<',$fullpath) ) {
                #print "  and fails the open() : $!\n";
            }

        }

    }
    return $numfiles;
}
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