boundary/website/content/partials/cmd-connect-env-vars.mdx

You also have access to some templated values that are substituted into the
command arguments, and these values are additionally injected as environment
variables in the executed command:

- `{{boundary.ip}}` (`BOUNDARY_PROXIED_IP`): The IP address of the listening
  socket that `boundary connect` has opened.
- `{{boundary.port}}` (`BOUNDARY_PROXIED_PORT`): The port of the listening
  socket that `boundary connect` has opened.
- `{{boundary.addr}}` (`BOUNDARY_PROXIED_ADDR`): The host:port format of the
  address. This is essentially equivalent to `{{boundary.ip}}:{{boundary.port}}`.