my $str = 'hello kitty 003x009 spanish';
$str =~ s/^(?:hello kitty )(\d+)(?:x\d+.*)$/sprintf "%d", $1/e;

print $str;

# result: 3
# expected: 'hello kitty 3x009 spanish'


##</code><code>##

$str =~ s/^(?:hello kitty )(\d+)(?:x\d+.*)$/XX/;