yamlfmt

I tried various beautifier of YAML files, but none of them satisfies me.

https://pypi.org/project/yamlfmt cannot handle a file with multiple YAML objects separated by ---.
https://github.com/devopyio/yamlfmt cannot handle multiple files.
https://github.com/miekg/yamlfmt/blob/master/fmt.go cannot replace (inline edit) the input files.

Usage

To beautify one or more files and write to stdout:
```
yamlfmt a.yaml b.yaml c.yaml
```
To beautify one or more files in the replace mode:
```
yamlfmt -w a.yaml b.yaml c.yaml
```
To beautify stdin and write to stdout:
```
cat a.yaml | yamlfmt
```
To beautify stdin and write to a file:
```
cat a.yaml | yamlfmt > b.yaml
```