You may try these 3 commands and report the result:
$ which ruby
$ ls -l `which ruby`
$ ls -l `which ruby | sed -e 's/ruby//'` | grep irb
In my case, the result is:
$ which ruby
/usr/bin/ruby
$ ls -l `which ruby`
lrwxrwxrwx 1 root root 43 2010-05-10 14:47 /usr/bin/ruby ->
/opt/ruby-enterprise-1.8.7-2010.01/bin/ruby
$ ls -l `which ruby | sed -e 's/ruby//'` | grep irb
lrwxrwxrwx 1 root root 42 2010-05-10 14:48 irb ->
/opt/ruby-enterprise-1.8.7-2010.01/bin/irb
-rwxr-xr-x 1 root root 376 2010-03-19 18:45 irb1.8
lrwxrwxrwx 1 root root 6 2010-03-31 17:00 irb-ORIG -> irb1.8
What it does is:
* use 'which' to find where you have ruby installed
* list the details about ruby (e.g. a symlink)
* search that same directory for the 'irb' command
That may give a hint where your ruby and irb are installed.
HTH,
Peter
"irb" +pressing TAB =C2=A0 =EF=BC=8Cnothing happen
=C2=A0"irb" +pressing TAB =C2=A0+ Space bar
pt@pt:~$ irb
.bash_history =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0.local/
.bash_logout =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 .mozilla/
.bashrc =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0Music/
.cache/ =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0.nautilus/
.compiz/ =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 p= hoto.tar.gz
.config/ =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 P= ictures/
.dbus/ =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 .pki/
Desktop/ =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 .= profile
.dmrc =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0Public/
Documents/ =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 .pulse= /
Downloads/ =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 .pulse= -cookie
.emacs.d/ =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0.= recently-used.xbel
.esd_auth =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0r= uby-1.9.2-p0/
examples.desktop =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 ruby-1.9.2-p0.tar.bz2
.fontconfig/ =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 .shotwell/
.gconf/ =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0.sudo_as_admin_successful
.gconfd/ =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 T= emplates/
.gksu.lock =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 .thumb= nails/
.gnome2/ =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 v= b
.gnome2_private/ =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 Videos/
.gstreamer-0.10/ =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 .VirtualBox/
.gtk-bookmarks =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 .xinput.d/
.gvfs/ =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 .xsession-errors
--=20
Peter Vandenabeele
gsm: +32-478-27.40.69
e-mail: (e-mail address removed)
http://twitter.com/peter_v