I am researching how to install Ruby 1.9.1 in Xubuntu 10.04 and I came across the command build-essential and build-dep multiple times. Sometimes it is followed by packages and sometimes it is both preceded and post-ceded by packages.

The 2 examples I am looking at are:

sudo apt-get install build-essential zlib1g zlib1g-dev zlibc libruby1.9 libxml2 libxml2-dev libxslt-dev

sudo apt-get build-dep ruby1.9

and

sudo apt-get install ruby irb ri rdoc ruby1.8-dev libzlib-ruby libyaml-ruby libreadline-ruby libncurses-ruby libcurses-ruby libruby libruby-extras libfcgi-ruby1.8 build-essential libopenssl-ruby libdbm-ruby libdbi-ruby libdbd-sqlite3-ruby sqlite3 libsqlite3-dev libsqlite3-ruby libxml-ruby libxml2-dev