This command

```
$ echo '一二三四五六七八九十' | grep -oE '[一-十]'

```

outputs:

```
一
二
三
五
六
七
八
九
十

```

The regex `[一-十]` (one to ten) is expected to match against Chinese numbers.
As the example shows, it matches against every Chinese number from one to ten, except the Chinese character `四` (four)。

Why?

Is this a bug or a joke?

I may think this as joke, because in Chinese '四' (four) sounds alike '事' (thing). In fact, in some dialects of Chinese, they share a same pronunciation. Thus '一二三五六七八九十' (one two three five six seven eight nine ten) implies '沒四' (no four), i.e. '沒事' (no thing)。

BTW, the version of the grep I use:

```
GNU grep 2.5.4

```