gistfile1.txt

$ cat .gemrc 
--- 
:verbose: true
:benchmark: false
:sources: 
- http://gems.rubyforge.org/
- http://gems.github.com
:update_sources: true
:backtrace: false
:bulk_threshold: 1000
rdoc: --inline-source --line-numbers --format=html --template=hanna

$ sudo gem install thoughtbot-shoulda
Successfully installed thoughtbot-shoulda-2.10.2
1 gem installed
Installing ri documentation for thoughtbot-shoulda-2.10.2...
Usage: gem [options] [names...]

  Files are parsed, and the information they contain collected, before any
  output is produced. This allows cross references between all files to be
  resolved. If a name is a directory, it is traversed. If no names are
  specified, all Ruby files in the current directory (and subdirectories) are
  processed.

  How RDoc generates output depends on the output formatter being used, and on
  the options you give.

  - Darkfish creates frameless HTML output by Michael Granger.

  - ri creates ri data files

Parsing Options:

    -a, --all                        Include all methods (not just public) in
                                     the output.

    -x, --exclude=PATTERN            Do not process files or directories
                                     matching PATTERN.

    -E, --extension=NEW=OLD          Treat files ending with .new as if they
                                     ended with .old. Using '-E cgi=rb' will
                                     cause xxx.cgi to be parsed as a Ruby file.

    -U, --force-update               Forces rdoc to scan all sources even if
                                     newer than the flag file.

        --pipe                       Convert RDoc on stdin to HTML

        --threads=THREADS            Number of threads to parse with.

Generator Options:

    -c, --charset=CHARSET            Specifies the output HTML character-set.

    -f, --fmt, --format=FORMAT       Set the output formatter.  One of:
                                       darkfish
                                       ri

    -i, --include=DIRECTORIES        Set (or add to) the list of directories to
                                     be searched when satisfying :include:
                                     requests. Can be used more than once.

    -N, --line-numbers               Include line numbers in the source code.

    -m, --main=NAME                  NAME will be the initial page displayed.

    -o, --output, --op=DIR           Set the output directory.

    -H, --show-hash                  A name of the form #name in a comment is a
                                     possible hyperlink to an instance method
                                     name. When displayed, the '#' is removed
                                     unless this option is specified.

    -w, --tab-width=WIDTH            Set the width of tab characters.

    -T, --template=NAME              Set the template used when generating
                                     output.

    -t, --title=TITLE                Set TITLE as the title for HTML output.

    -W, --webcvs=URL                 Specify a URL for linking to a web frontend
                                     to CVS. If the URL contains a '%s', the
                                     name of the current file will be
                                     substituted; if the URL doesn't contain a
                                     '%s', the filename will be appended to it.

Diagram Options:

    -I, --image-format=FORMAT        Sets output image format for diagrams. Can
                                     be gif, png, jpg, jpeg. If this option
                                     is omitted, png is used. Requires
                                     diagrams.

    -d, --diagram                    Generate diagrams showing modules and
                                     classes. You need dot V1.8.6 or later to
                                     use the --diagram option correctly. Dot is
                                     available from http://graphviz.org

    -F, --fileboxes                  Classes are put in boxes which represents
                                     files, where these classes reside. Classes
                                     shared between more than one file are
                                     shown with list of files that are sharing
                                     them. Silently discarded if --diagram is
                                     not given.

ri Generator Options:

    -r, --ri                         Generate output for use by `ri`. The files
                                     are stored in the '.rdoc' directory under
                                     your home directory unless overridden by a
                                     subsequent --op parameter, so no special
                                     privileges are needed.

    -R, --ri-site                    Generate output for use by `ri`. The files
                                     are stored in a site-wide directory,
                                     making them accessible to others, so
                                     special privileges are needed.

    -M, --merge                      When creating ri output, merge previously
                                     processed classes into previously
                                     documented classes of the same name.

Generic Options:

    -D, --debug                      Displays lots on internal stuff.
    -q, --quiet                      Don't show progress as we parse.
    -v, --verbose                    Display extra progress as we parse.

Deprecated options - these warn when set

    -S, --inline-source
    -p, --promiscuous


invalid argument: --format=html

===========================================================================================
If I remove the last rdoc :

$ gem list rdoc

*** LOCAL GEMS ***

rdoc (2.4.3, 2.3.0)

$ sudo gem uninstall rdoc -v=2.4.3
Successfully uninstalled rdoc-2.4.3

===========================================================================================
And then trying again :

$ sudo gem install thoughtbot-shoulda
Successfully installed thoughtbot-shoulda-2.10.2
1 gem installed
Installing ri documentation for thoughtbot-shoulda-2.10.2...
Updating ri class cache with 7988 classes...
Installing RDoc documentation for thoughtbot-shoulda-2.10.2...

Working !