Don't show result of evaluating comments.

lib/pry/pry_instance.rb

@@ -309,7 +309,9 @@ class Pry
       end
     end
 
-    @suppress_output = true if eval_string =~ /;\Z/ || eval_string.empty?
+    if eval_string =~ /;\Z/ || eval_string.empty? || eval_string =~ /\A *#.*\n\z/
+      @suppress_output = true
+    end
 
     exec_hook :after_read, eval_string, self
     eval_string

test/test_pry_output.rb

@@ -38,4 +38,25 @@ describe Pry do
       mock_pry("class NastyClass; undef pretty_inspect; end", "NastyClass.new").should =~ /#<NastyClass:0x.*?>/
     end
   end
+
+  describe "output suppression" do
+    before do
+      @t = pry_tester
+    end
+    it "should normally output the result" do
+      mock_pry("1 + 2").should == "=> 3\n\n"
+    end
+
+    it "should not output anything if the input ends with a semicolon" do
+      mock_pry("1 + 2;").should == "\n"
+    end
+
+    it "should output something if the input ends with a comment" do
+      mock_pry("1 + 2 # basic addition").should == "=> 3\n\n"
+    end
+
+    it "should not output something if the input is only a comment" do
+      mock_pry("# basic addition").should == "\n"
+    end
+  end
 end