这是来自spec –help.

spec --help

-f,--format FORMAT[:WHERE]      Specifies what format to use for output. Specify WHERE to tell
                                    the formatter where to write the output. All built-in formats
                                    expect WHERE to be a file name,and will write to $stdout if it's
                                    not specified. The --format option may be specified several times
                                    if you want several outputs

                                    Builtin formats:
                                    silent|l                 : No output
                                    progress|p               : Text-based progress bar
                                    profile|o                : Text-based progress bar with profiling of 10 slowest examples
                                    specdoc|s                : Code example doc strings
                                    nested|n                 : Code example doc strings with nested groups indented
                                    html|h                   : A nice HTML report
                                    failing_examples|e       : Write all failing examples - input for --example

                                failing_example_groups|g : Write all failing example groups - input for --example

如何通过rake任务传递-f specdoc.