[update @ 15-03-09]
Updated the script to use the latest passenger 2.1.2 and the lastest version of Ruby Enterprise. Also made a few changes as suggested in the comments, thanks guys!

I needed a small project that I could use to learn some basic bash scripting. Since I like automating things a unattended passenger installation seemed like a cool thing. It’s far from perfect but it gets the job done. (on Ubuntu 8.04/8.10 at least).

Feel free to post any improvements you may have.

#!/bin/bash
#!/bin/bash
# Unattended REE/Passenger installation
# Source: http://weblog.brightlight-ict.nl/2008/12/unattended-passenger-ruby-enterprise-installation-on-ubuntu-8/
 
if [ "$(whoami)" != "root" ]; then
  echo "You need to be root to run this!"
  exit 2
fi
 
VERSION="1.2"
REEV="http://rubyforge.org/frs/download.php/51100/ruby-enterprise-1.8.6-20090201.tar.gz"
REEF="ruby-enterprise-1.8.6-20090201.tar.gz"
REEFF=${REEF%".tar.gz"}
PASSENGER="2.1.2"
export PASSENGER
 
echo "#####################################"
echo "Welcome, let's get this party rollin'"
echo "#####################################"
 
echo "Updating Aptitude"
apt-get update
 
echo "Installing build essentials"
apt-get install build-essential zlib1g-dev libssl-dev wget libreadline5-dev -y
 
echo "Installing GIT"
apt-get install -y git-core
 
echo "Installing apache"
apt-get install -y apache2
 
echo "Installing apache headers"
apt-get install -y apache2-prefork-dev
 
echo "Installing Ruby Enterprise from following url"
echo $REEV
wget $REEV
 
if [ -e $REEF ]
then
  echo "File downloaded succesful"
 
else
  echo "Error, file wasn't downloaded!"
  exit
fi
 
tar -zxvf $REEF
# possible options perhaps for checker
# --extra rails --no-tcmalloc
 
if [ -d ./$REEFF ]
then
   ./$REEFF/installer --auto /opt/ruby
  echo "Dir test"
else
  echo "Dir not found, exiting.."
  exit
fi
 
echo "Creating ruby symlinks"
ln -s /opt/ruby/bin/ruby /usr/bin/ruby
ln -s /opt/ruby/bin/gem /usr/bin/gem
ln -s /opt/ruby/bin/rake /usr/bin/rake
ln -s /opt/ruby/bin/rails /usr/bin/rails
 
echo "Installing other gems"
gem install rails
gem install will_paginate
gem install shoulda
gem install mysql
 
echo "Installing passenger"
gem install passenger -v=$PASSENGER
 
echo "Config passenger"
yes '' | /opt/ruby/bin/passenger-install-apache2-module
 
 
echo "Copying passenger files"
touch /etc/apache2/mods-available/passenger.load
touch /etc/apache2/mods-available/passenger.conf
 
echo "LoadModule passenger_module /opt/ruby/lib/ruby/gems/1.8/gems/passenger-$PASSENGER/ext/apache2/mod_passenger.so" >> /etc/apache2/mods-available/passenger.load
echo "PassengerRoot /opt/ruby/lib/ruby/gems/1.8/gems/passenger-$PASSENGER 
PassengerRuby /opt/ruby/bin/ruby" >> /etc/apache2/mods-available/passenger.conf
 
echo "Enabling passenger module"
a2enmod passenger
 
echo "Reloading apache"
/etc/init.d/apache2 reload
 
echo "##########################"
echo "# Installation Complete"
echo "##########################"
sleep 2
echo "##########################"
echo "# Installed Ruby Version #"
echo "##########################"
ruby -v
echo "##########################"
echo "# Installed Gems Version #"
echo "##########################"
gem -v
/opt/ruby/bin/passenger-status

You can find the gist here