use warnings;
use strict;

my %umlautWords;
my $umlautWordPattern = qr( [aou]e )ixo;

for my $file ( glob( 'C:/myPath/*.txt' ) ) {
    my $data;
    open( my $FH, '<', $file ) or next;
    {
        local $/;
        $data = <$FH>;
    }
    close $FH;
    
    while ( $data =~ / \b (\w+) \b /oxg ) {
        my $word = $1;
        if ( $word =~ $umlautWordPattern ) {
            next if exists $umlautWords{ $word };
            $umlautWords{ $word } = 1;
        }
    }
    print "$file completed\n";
}

print "$_\n" for ( sort { uc( $a ) cmp uc( $b ) } keys %umlautWords );