diff --git a/lib/gcovinator.rb b/lib/gcovinator.rb
index 9faf1a9..230def9 100644
--- a/lib/gcovinator.rb
+++ b/lib/gcovinator.rb
@@ -1,12 +1,30 @@
 require_relative "gcovinator/version"
+require "tmpdir"
 
 module Gcovinator
 
   class << self
 
     def run(build_dir, source_dirs, files, output_dir)
+      build_dir = File.expand_path(build_dir)
       source_dirs = ["."] if source_dirs.empty?
+      source_dirs = source_dirs.map do |s|
+        File.expand_path(s)
+      end
       files = Dir["#{build_dir}/**/*.gcda"] if files.empty?
+      files = files.map do |f|
+        File.expand_path(f)
+      end
+      output_dir = File.expand_path(output_dir)
+      Dir.mktmpdir do |dir|
+        Dir.chdir(dir) do
+          files.each do |f|
+            IO.popen(["gcov", "-bmi", f]) do |io|
+              io.read
+            end
+          end
+        end
+      end
     end
 
   end
diff --git a/lib/gcovinator/cli.rb b/lib/gcovinator/cli.rb
index 25880fc..b1a530c 100644
--- a/lib/gcovinator/cli.rb
+++ b/lib/gcovinator/cli.rb
@@ -46,7 +46,7 @@ module Gcovinator
 
         end.parse!(argv)
 
-        Gcovinator.run(build_dir, source_dirs, argv)
+        Gcovinator.run(build_dir, source_dirs, argv, output_dir)
       end
 
     end