added a Pry#run_command method

Useful when pry instance is passed to procs such as exception handlers
e.g Pry.config.exception_handler = proc |output, value, _pry_|
      _pry_.run_command('cat --ex')
    end

Notw that run_command also accepts a optional second parameter 'binding' that defaults to binding_stack.last when not given

lib/pry/pry_instance.rb

@@ -319,6 +319,16 @@ class Pry
     end
   end
 
+  # Run the specified command.
+  # @param [String] The command (and its params) to execute.
+  # @param [Binding] The binding to use..
+  # @example
+  #   pry_instance.run_command("ls -m")
+  def run_command(val, target = binding_stack.last)
+    process_line(val, "", target)
+    Pry::CommandContext::VOID_VALUE
+  end
+
   # Set the last result of an eval.
   # This method should not need to be invoked directly.
   # @param [Object] result The result.

test/test_pry.rb

@@ -187,6 +187,19 @@ describe Pry do
       end
     end
 
+    describe "Pry#run_command" do
+      it 'should run a command in a specified context' do
+        b = Pry.binding_for(7)
+        p = Pry.new(:output => StringIO.new)
+        p.run_command("ls -m", b)
+        p.output.string.should =~ /divmod/
+      end
+
+      it 'should run a command in the context of a session' do
+        mock_pry("@session_ivar = 10", "_pry_.run_command('ls')").should =~ /@session_ivar/
+      end
+    end
+
     describe "repl" do
       describe "basic functionality" do
         it 'should set an ivar on an object and exit the repl' do