sub replace {
    my($text, $pattern, $replacement, $global) = @_;
    my $result = $text;
    if ($global) {
       $result =~ s/$pattern/$replacement/eg;
    } else {
       $result =~ s/$pattern/$replacement/e;
    }
    return $result;
}

my $y = replace($x, qr/\b(\w)/is, '"\U$1"', 1);