only interpolate once during command processing (fixes #200)

lib/pry/command_processor.rb

@@ -53,23 +53,20 @@ class Pry
     #   interpolation against.
     # @return [Array] The command data and arg string pair
     def command_matched(val, target)
-      _, cmd_data = commands.commands.find do |name, data|
+      interpolated_val = begin
+                           interpolate_string(val, target)
+                         rescue Exception
+                           nil
+                         end
 
+      _, cmd_data = commands.commands.find do |name, data|
         prefix = convert_to_regex(Pry.config.command_prefix)
         prefix = "(?:#{prefix})?" unless data.options[:use_prefix]
 
         command_regex = /^#{prefix}#{convert_to_regex(name)}(?!\S)/
 
         if data.options[:interpolate]
-          # If interpolation fails then the command cannot be matched,
-          # so early exit.
-          begin
-            interp_val = interpolate_string(val, target)
-          rescue Exception
-            next
-          end
-
-          val.replace interp_val if command_regex =~ interp_val
+          val.replace interpolated_val if command_regex =~ interpolated_val
         else
           command_regex =~ val
         end

test/test_command_processor.rb

@@ -245,11 +245,21 @@ describe "Pry::CommandProcessor" do
   end
 
 
-  it 'commands that have :interpolate => false should not be interpolated (interpolate_string should *not* be called)' do
+  it 'should not interpolate commands that have :interpolate => false (interpolate_string should *not* be called)' do
     @pry.commands.command("boast", "", :interpolate => false) {}
 
     # remember to use '' instead of "" when testing interpolation or
     # you'll cause yourself incredible confusion
     lambda { @command_processor.command_matched('boast #{c}', binding) }.should.not.raise NameError
   end
+
+  it 'should only execute the contents of an interpolation once' do
+    $obj = 'a'
+
+    redirect_pry_io(InputTester.new('#{$obj.succ!}'), StringIO.new) do
+      Pry.new.rep
+    end
+
+    $obj.should == 'b'
+  end
 end

test/test_pry.rb

@@ -517,7 +517,7 @@ describe Pry do
             $test_interpolation = nil
           end
 
-          # bug fix for https://github.com/banister/pry/issues/170
+          # bug fix for https://github.com/pry/pry/issues/170
           it 'should not choke on complex string interpolation when checking if ruby code is a command' do
             redirect_pry_io(InputTester.new('/#{Regexp.escape(File.expand_path("."))}/'), str_output = StringIO.new) do
               pry