update-alternatives-install-ruby.sh

# Installs ruby1.8 ruby1.9 ruby1.9.1 found on Lucid as alternatives. Easily switch between them.
# Originally from: http://groups.google.com/group/rails-oceania/browse_thread/thread/8a2b256d117db49f

# become root 
su

# make sure the packages are installed for 1.8 & 1.9 
aptitude install -s  ~n^ruby1.[89]$ ~n^irb1.[89]$ ~n^ri1.[89]

# install ruby1.8 & friends with priority 500 
# so this will be the default "auto" choice 
update-alternatives --install /usr/bin/ruby ruby /usr/bin/ruby1.8 500 --slave /usr/share/man/man1/ruby.1.gz ruby.1.gz /usr/share/man/man1/ruby1.8.1.gz --slave /usr/bin/ri ri /usr/bin/ri1.8 --slave /usr/bin/irb irb /usr/bin/irb1.8

# install ruby1.9.1 & friends with priority 400 
update-alternatives --install /usr/bin/ruby ruby /usr/bin/ruby1.9.1 400 --slave /usr/share/man/man1/ruby.1.gz ruby.1.gz /usr/share/man/man1/ruby1.9.1.1.gz --slave /usr/bin/ri ri /usr/bin/ri1.9.1 --slave /usr/bin/irb irb /usr/bin/irb1.9.1

# install ruby1.9 & friends with priority 400 
update-alternatives --install /usr/bin/ruby ruby /usr/bin/ruby1.9 400 --slave /usr/bin/gem gem /usr/bin/gem1.8 --slave /usr/share/man/man1/ruby.1.gz ruby.1.gz /usr/share/man/man1/ruby1.9.1.gz --slave /usr/bin/ri ri /usr/bin/ri1.9 --slave /usr/bin/irb irb /usr/bin/irb1.9

# choose your interpreter 
# changes symlinks for /usr/bin/ruby , 
# /usr/bin/irb, /usr/bin/ri and man (1) ruby 
update-alternatives --config ruby