I won’t cover aquiring the Command-T source files. I recommend the pathogen method though. In order to install Command-T on Vim, it is necessary to have vim compiled with ruby. This is easily accomplished by installing vim-nox.

sudo apt-get install vim-nox

After installing vim you can try to make the extension by changing to the ruby/command-t directory within the Command-t source directory. And executing the following:

/command-t/ruby/command-t$ ruby extconf.rb

You are likely to run into the following problem:

/usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require': cannot load such file -- mkmf (LoadError)
        from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
		        from extconf.rb:24:in `''`

The solution is to install ruby1.9.1-dev:

sudo apt-get install ruby1.9.1-dev

After installing you should be able to proceed:

command-t/ruby/command-t$ ruby extconf.rb
checking for ruby.h... yes
creating Makefile

Finish with the make command:

$ make
linking shared-object ext.so

Command-t should now be working.