How to convert json to yaml and vice versa in command line?

How convert JSON file into YAML and vice versa in command line?

Any ways are welcome.

Update: as of yq version 4.18:

The flags -p and -o let you specify input and output formats. You can convert between yaml, json, and xml!

yq -p json -o yaml file.json # json -> yaml
yq -p json -o xml file.json  # json -> xml
yq -p yaml -o json file.yaml # yaml -> json
yq -p yaml -o xml file.yaml  # yaml -> xml
yq -p xml -o json file.xml   # xml -> json
yq -p xml -o yaml file.xml   # xml -> yaml

With yq version 4.8.0:

yq e -P file.json yields YAML

yq e -j file.yaml yields JSON

• e or eval evaluates each file separately. ea or eval-all merges them first.
• -P or --prettyPrint outputs YAML
• -j or --tojson outputs JSON