1. Download the Java JAR (https://oss.sonatype.org/content/repositories/snapshots/org/openapitools/openapi-generator-cli/4.1.2-SNAPSHOT/openapi-generator-cli-4.1.2-20190904.113123-33.jar)

2. Rename the JAR as "openapi-generator-cli.jar"

3. Run the following command to generate an gRPC, Protobuf definitions for the Petstore API (https://raw.githubusercontent.com/OpenAPITools/openapi-generator/master/modules/openapi-generator/src/test/resources/2_0/petstore.yaml):

Mac/Linux:

java -jar openapi-generator-cli.jar generate -g grpc-schema -i https://raw.githubusercontent.com/OpenAPITools/openapi-generator/master/modules/openapi-generator/src/test/resources/2_0/petstore.yaml -o /var/tmp/grpc-schema/ Windows:

java -jar openapi-generator-cli.jar generate -g grpc-schema -i https://raw.githubusercontent.com/OpenAPITools/openapi-generator/master/modules/openapi-generator/src/test/resources/2_0/petstore.yaml -o C:\tmp\grpc-schema

Project page: https://github.com/OpenAPITools/openapi-generator