Function open_backend 

pub fn open_backend(backend: ShellBackend) -> Result<Box<dyn Shell>, ShellError>

Opens a specific backend, ignoring BACKEND_ENV_VAR.

For crcbl CLI subcommands that must be headless whatever the environment says, and for tests.

Errors

ShellError::UnknownBackend if this build has no such backend, or the backend’s own error if it fails to open.