What you are saying is very likely incorrect. You or someone else must 
have screwed up the links to ruby and irb in {{ /usr/bin }}. If you do 
the following you should get a similar result as I will list below:

  $ cd /usr/bin/
  $ ls -l ruby*
  lrwxrwxrwx 1 root root    7 2009-02-27 13:52 ruby -> ruby1.8
  -rwxr-xr-x 1 root root 3564 2008-10-09 20:19 ruby1.8
  lrwxrwxrwx 1 root root    7 2008-10-28 12:51 ruby1.8-old-LINK -> 
ruby1.8
  -rwxr-xr-x 1 root root 3676 2008-01-24 07:02 ruby1.9
  -rwxr-xr-x 1 root root 6320 2007-12-07 05:09 
ruby-glade-create-template

  $ ls -l irb*
  lrwxrwxrwx 1 root root   6 2008-10-28 13:15 irb -> irb1.9
  -rwxr-xr-x 1 root root 376 2008-10-09 20:14 irb1.8
  -rwxr-xr-x 1 root root 376 2008-01-24 06:54 irb1.9

As you see {{ ruby }} and {[ irb }} should be symbolic links to their 
respective version binaries. To change the the behavior you can change 
these links.

For instance If I wish to make my {{ irb }} to point to {{ 1.8 irb }}, I 
would do the following as {{ root }} or with the help of {{ sudo }}:

  1) mv /usr/irb /usr/irb.old
  2) ln -s /usr/bin/irb1.8 /usr/irb

If you are not sure you understand the above procedure I suggest you do 
not do anything on your own without some more help from people on the 
forum. For starters you should post the results of the following here:

  $ cd /usr/bin/
  $ ls -l ruby*
  $ ls -l irb*
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