Currently, I am developing with 3 different versions of Ruby:

• MRI Ruby 1.8.7,

• MRI Ruby 1.9.1,

• JRuby 1.4.0

I need a quick way to switch between the three main Ruby executables, and the related other programs (gem, irb, etc).

I have set up Debian Alternatives to handle the job.

Alternatives with Ruby

The programs I want to switch are:

• ruby

• gem

• irb

• ri

• rake

• rails

Ruby MRI 1.8 and 1.9

If you compiled your own ruby 1.8 and 1.9, make sure you indicate the version:

$ ./configure --program-suffix=1.9

Install JRuby

See my other post.

Create Links from /etc/alternatives to /usr/bin

$ cd /usr/bin
$ sudo ln -s /etc/alternatives/ruby
$ sudo ln -s /etc/alternatives/irb
$ sudo ln -s /etc/alternatives/ri
$ sudo ln -s /etc/alternatives/rake
$ sudo ln -s /etc/alternatives/gem

Create Ruby Alternatives

$ sudo update-alternatives \
  --install  /usr/bin/ruby  ruby  /usr/local/bin/ruby1.9   30 \
  --slave    /usr/bin/irb   irb   /usr/local/bin/irb1.9       \
  --slave    /usr/bin/gem   gem   /usr/local/bin/gem1.9       \
  --slave    /usr/bin/ri    ri    /usr/local/bin/ri1.9        \
  --slave    /usr/bin/rails rails /usr/local/bin/rails1.9     \
  --slave    /usr/bin/rake  rake  /usr/local/bin/rake1.9

$ sudo update-alternatives \
  --install  /usr/bin/ruby  ruby  /usr/bin/ruby1.8   20 \
  --slave    /usr/bin/irb   irb   /usr/bin/irb1.8       \
  --slave    /usr/bin/ri    ri    /usr/bin/ri1.8        \
  --slave    /usr/bin/gem   gem   /usr/bin/gem1.8       \
  --slave    /usr/bin/rails rails /usr/bin/rails1.8     \
  --slave    /usr/bin/rake  rake  /usr/bin/rake1.8

$ sudo update-alternatives \
  --install  /usr/bin/ruby  ruby  /usr/local/lib/jruby/bin/jruby   10 \
  --slave    /usr/bin/irb   irb   /usr/local/lib/jruby/bin/jirb       \
  --slave    /usr/bin/ri    ri    /usr/local/lib/jruby/bin/ri         \
  --slave    /usr/bin/rails rails /usr/local/lib/jruby/bin/rails      \
  --slave    /usr/bin/gem   gem   /usr/local/lib/jruby/bin/gem        \
  --slave    /usr/bin/rake  rake  /usr/local/lib/jruby/bin/rake

Check the result

$ update-alternatives --display ruby
ruby - auto mode
 link currently points to /usr/local/bin/ruby1.9
/usr/bin/ruby1.8 - priority 20
 slave gem: /usr/bin/gem1.8
 slave irb: /usr/bin/irb1.8
 slave rails: /usr/bin/rails1.8
 slave rake: /usr/bin/rake1.8
 slave ri: /usr/bin/ri1.8
/usr/local/bin/ruby1.9 - priority 30
 slave gem: /usr/local/bin/gem1.9
 slave irb: /usr/local/bin/irb1.9
 slave rails: /usr/local/bin/rails1.9
 slave rake: /usr/local/bin/rake1.9
 slave ri: /usr/local/bin/ri1.9
/usr/local/lib/jruby/bin/jruby - priority 10
 slave gem: /usr/local/lib/jruby/bin/gem
 slave irb: /usr/local/lib/jruby/bin/jirb
 slave rails: /usr/local/lib/jruby/bin/rails
 slave rake: /usr/local/lib/jruby/bin/rake
 slave ri: /usr/local/lib/jruby/bin/ri
Current `best' version is /usr/local/bin/ruby1.9.

Switch versions

$ sudo update-alternatives --config ruby
There are 3 choices for the alternative ruby (providing /usr/bin/ruby).

  Selection    Path                            Priority   Status
------------------------------------------------------------
* 0            /usr/local/bin/ruby1.9           30        auto mode
  1            /usr/bin/ruby1.8                 20        manual mode
  2            /usr/local/bin/ruby1.9           30        manual mode
  3            /usr/local/lib/jruby/bin/jruby   10        manual mode

Press enter to keep the current choice[*], or type selection number: 1
Using '/usr/bin/ruby1.8' to provide 'ruby'.