>> Sorry, this should just have been $PATH.
> Ah, ok. "echo $PATH" gives
> /Applications/TextMate.app/Contents/SharedSupport/Support/bin/
> CocoaDialog.app/Contents/MacOS:/opt/local/bin:/opt/local/sbin:/bin:/
> sbin:/usr/bin:/usr/sbin:/Applications/TextMate.app/Contents/
> SharedSupport/Support/bin

Try 'type -a ruby'.

ruby is /usr/bin/ruby

Try also: PATH=/usr/bin which ruby

]2; /Users/cassio/Desktop]1; cassio/Desktop/usr/bin/ruby

which looks suspicious...