how to load env variables from .env file in task

the

source

source

source

source shell command is not available. I tried

 "tasks": {
    "my-task": "export .env && my-command",
  }

 "tasks": {
    "my-task": "export .env && my-command",
  }

 "tasks": {
    "my-task": "export .env && my-command",
  }

 "tasks": {
    "my-task": "export .env && my-command",
  }

is that correct? it's not working now. Where can I see what commands are available in tasks?