On Sat, May 22, 2010 at 2:47 PM, pepe <p...@betterrpg.com> wrote:
> Just in case it applies here is an extract from the Pickaxe book
> (Second edition, page 217):
>
> "Threre's a subtlety when it comes to installing different versions of
> the same application with RubyGems. Even though RubyGems keeps
> separate versions of the application's library files, it does not
> version the actual command you use to run the application. As a
> result, each install of an application effectively overwrites the
> previous one."

That's actually not the whole story, and excerpt from the output of
gem help install:

 Description:
    The install command installs local or remote gem into a gem repository.

    For gems with executables ruby installs a wrapper file into the executable
    directory by default.  This can be overridden with the --no-wrappers option.
    The wrapper allows you to choose among alternate gem versions using
    _version_.

    For example `rake _0.7.3_ --version` will run rake version 0.7.3 if a newer
    version is also installed.

The "actual command you use to run the application"  is actually a bit
of boilerplate generated by gems which requires the gem and then calls
the executable in the bin directory of the gem.  If you use that
_{version}_ option it requires a specific version of the gem.

So if you have both rails 2.3.5 and 1.2.6 installed then either

rails
or
rails _2.3.5_

will run version 2.3.5 which is the latest version installed.  but

rails _1.2.6_

will run version 1.2.6

HTH


BTW, the OP gave rails version 1.3.5 as a example, as far as I know
this a fictitious version since rails went from version 1.2.6 to
version 2.0.0

-- 
Rick DeNatale

Blog: http://talklikeaduck.denhaven2.com/
Github: http://github.com/rubyredrick
Twitter: @RickDeNatale
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