diff --git a/CHANGELOG.md b/CHANGELOG.md
index 49afb30a53..4240a6bbce 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -59,10 +59,6 @@
 
   * [ExUnit.Formatter] `:case_started` and `:case_finished` events are deprecated in favor of `:module_started` and `:module_finished`
 
-#### Mix
-
-  * [Mix.Shell] The `cmd/2` callback is deprecated in favor of `System.cmd/3` and `Mix.Shell.cmd/3`
-
 ### 4. Deprecations
 
 #### Elixir
diff --git a/lib/mix/lib/mix/scm/git.ex b/lib/mix/lib/mix/scm/git.ex
index ecf05df460..6603fb8248 100644
--- a/lib/mix/lib/mix/scm/git.ex
+++ b/lib/mix/lib/mix/scm/git.ex
@@ -107,6 +107,8 @@ defmodule Mix.SCM.Git do
   end
 
   defp checkout(_path, opts) do
+    Mix.shell.print_app()
+
     # Set configuration
     sparse_toggle(opts)
     update_origin(opts[:git])
@@ -244,13 +246,20 @@ defmodule Mix.SCM.Git do
     :ok
   end
 
-  defp git!(args, into \\ %Mix.Shell{}) do
+  defp git!(args, into \\ default_into()) do
     case System.cmd("git", args, into: into, stderr_to_stdout: true) do
       {response, 0} -> response
       {_, _} -> Mix.raise("Command \"git #{Enum.join(args, " ")}\" failed")
     end
   end
 
+  defp default_into() do
+    case Mix.shell do
+      Mix.Shell.IO -> IO.stream(:stdio, :line)
+      _ -> ""
+    end
+  end
+
   defp assert_git! do
     case Mix.State.fetch(:git_available) do
       {:ok, true} ->
diff --git a/lib/mix/lib/mix/shell.ex b/lib/mix/lib/mix/shell.ex
index 18406cf1e3..e3812b7d08 100644
--- a/lib/mix/lib/mix/shell.ex
+++ b/lib/mix/lib/mix/shell.ex
@@ -14,9 +14,27 @@ defmodule Mix.Shell do
   @callback error(message :: IO.ANSI.ansidata()) :: :ok
 
   @doc """
-  Writes data directly into the shell.
+  Executes the given command and returns its exit status.
   """
-  @callback write(message :: binary) :: :ok
+  @callback cmd(command :: String.t) :: integer
+
+  @doc """
+  Executes the given command and returns its exit status.
+
+  ## Options
+
+    * `:print_app` - when `false`, does not print the app name
+      when the command outputs something
+
+    * `:stderr_to_stdout` - when `false`, does not redirect
+      stderr to stdout
+
+    * `:quiet` - when `true`, do not print the command output
+
+    * `:env` - environment options to the executed command
+
+  """
+  @callback cmd(command :: String.t, options :: keyword) :: integer
 
   @doc """
   Prompts the user for input.
@@ -34,34 +52,6 @@ defmodule Mix.Shell do
   """
   @callback print_app() :: :ok
 
-  @doc """
-  A collectable shell struct.
-  """
-  defstruct print_app?: true
-
-  defimpl Collectable do
-    def into(%Mix.Shell{print_app?: print_app?} = original) do
-      fun = fn
-        {:cont, shell}, {:cont, data} ->
-          shell.write(data)
-          {:cont, shell}
-
-        {:print, shell}, {:cont, data} ->
-          shell.print_app()
-          shell.write(data)
-          {:cont, shell}
-
-        _, _ ->
-          original
-      end
-
-      case print_app? do
-        true -> {{:print, Mix.shell()}, fun}
-        false -> {{:cont, Mix.shell()}, fun}
-      end
-    end
-  end
-
   @doc """
   Returns the printable app name.
 
@@ -77,8 +67,20 @@ defmodule Mix.Shell do
     Mix.ProjectStack.printable_app_name()
   end
 
-  @doc false
-  # TODO: Deprecate on Mix v1.8
+  @doc """
+  Executes the given `command` as a shell command and
+  invokes the `callback` for the streamed response.
+
+  This is most commonly used by shell implementations
+  but can also be invoked directly.
+
+  ## Options
+
+    * `:stderr_to_stdout` - redirects stderr to stdout, defaults to true
+    * `:env` - a list of environment variables, defaults to `[]`
+    * `:quiet` - overrides the callback to no-op
+
+  """
   def cmd(command, options, callback) when is_function(callback, 1) do
     callback =
       if Keyword.get(options, :quiet, false) do
@@ -87,33 +89,6 @@ defmodule Mix.Shell do
         callback
       end
 
-    fun = fn
-      _, {:cont, data} -> callback.(data)
-      _, _ -> :ok
-    end
-
-    cmd(command, options, :ok, fun)
-  end
-
-  def cmd(command, callback) when is_function(callback, 1) do
-    cmd(command, [], callback)
-  end
-
-  @doc """
-  Executes the given `string` as a shell command.
-
-    * `:into` - a collectable to print the result to, defaults to `""`
-    * `:stderr_to_stdout` - redirects stderr to stdout, defaults to true
-    * `:env` - a list of environment variables, defaults to `[]`
-
-  """
-  def cmd(command, options) when is_binary(command) and is_list(options) do
-    collectable = Keyword.get(options, :into, "")
-    {acc, callback} = Collectable.into(collectable)
-    cmd(command, options, acc, callback)
-  end
-
-  defp cmd(command, options, acc, callback) do
     env = validate_env(Keyword.get(options, :env, []))
 
     args =
@@ -125,16 +100,16 @@ defmodule Mix.Shell do
 
     opts = [:stream, :binary, :exit_status, :hide, :use_stdio, {:env, env} | args]
     port = Port.open({:spawn, shell_command(command)}, opts)
-    port_read(port, acc, callback)
+    port_read(port, callback)
   end
 
-  defp port_read(port, acc, callback) do
+  defp port_read(port, callback) do
     receive do
       {^port, {:data, data}} ->
-        port_read(port, callback.(acc, {:cont, data}), callback)
+        _ = callback.(data)
+        port_read(port, callback)
 
       {^port, {:exit_status, status}} ->
-        callback.(acc, :done)
         status
     end
   end
diff --git a/lib/mix/lib/mix/shell/io.ex b/lib/mix/lib/mix/shell/io.ex
index d4b1072b20..252148db35 100644
--- a/lib/mix/lib/mix/shell/io.ex
+++ b/lib/mix/lib/mix/shell/io.ex
@@ -19,11 +19,6 @@ defmodule Mix.Shell.IO do
     :ok
   end
 
-  @doc """
-  Writes data directly into the shell.
-  """
-  defdelegate write(data), to: IO
-
   @doc """
   Prints the given ANSI message to the shell followed by a newline.
   """
@@ -66,8 +61,10 @@ defmodule Mix.Shell.IO do
     [:red, :bright, message]
   end
 
-  @doc false
-  # TODO: Deprecate on Elixir v1.8
+  @doc """
+  Executes the given command and prints its output
+  to stdout as it comes.
+  """
   def cmd(command, opts \\ []) do
     print_app? = Keyword.get(opts, :print_app, true)
 
diff --git a/lib/mix/lib/mix/shell/process.ex b/lib/mix/lib/mix/shell/process.ex
index c1dd448b19..a32dacd753 100644
--- a/lib/mix/lib/mix/shell/process.ex
+++ b/lib/mix/lib/mix/shell/process.ex
@@ -65,14 +65,6 @@ defmodule Mix.Shell.Process do
     end
   end
 
-  @doc """
-  Forwards the message to the current process.
-  """
-  def write(data) do
-    send(self(), {:mix_shell, :write, [data]})
-    :ok
-  end
-
   @doc """
   Forwards the message to the current process.
   """
@@ -154,8 +146,10 @@ defmodule Mix.Shell.Process do
     end
   end
 
-  @doc false
-  # TODO: Deprecate on Elixir v1.8
+  @doc """
+  Executes the given command and forwards its messages to
+  the current process.
+  """
   def cmd(command, opts \\ []) do
     print_app? = Keyword.get(opts, :print_app, true)
 
diff --git a/lib/mix/lib/mix/shell/quiet.ex b/lib/mix/lib/mix/shell/quiet.ex
index ac37780860..e4634e97a5 100644
--- a/lib/mix/lib/mix/shell/quiet.ex
+++ b/lib/mix/lib/mix/shell/quiet.ex
@@ -14,11 +14,6 @@ defmodule Mix.Shell.Quiet do
   """
   defdelegate print_app, to: Mix.Shell.IO
 
-  @doc """
-  Writes nothing to the shell.
-  """
-  def write(_data), do: :ok
-
   @doc """
   Prints nothing to the shell.
   """
@@ -44,8 +39,9 @@ defmodule Mix.Shell.Quiet do
   """
   defdelegate yes?(message), to: Mix.Shell.IO
 
-  @doc false
-  # TODO: Deprecate on Elixir v1.8
+  @doc """
+  Executes the given command quietly without outputting anything.
+  """
   def cmd(command, opts \\ []) do
     Mix.Shell.cmd(command, opts, fn data -> data end)
   end
diff --git a/lib/mix/lib/mix/tasks/cmd.ex b/lib/mix/lib/mix/tasks/cmd.ex
index 0b7c998ff1..a93fe2b1a0 100644
--- a/lib/mix/lib/mix/tasks/cmd.ex
+++ b/lib/mix/lib/mix/tasks/cmd.ex
@@ -24,7 +24,7 @@ defmodule Mix.Tasks.Cmd do
     {args, apps} = parse_apps(args, [])
 
     if apps == [] or Mix.Project.config()[:app] in apps do
-      case Mix.Shell.cmd(Enum.join(args, " "), into: %Mix.Shell{}) do
+      case Mix.shell.cmd(Enum.join(args, " ")) do
         0 -> :ok
         status -> exit(status)
       end
diff --git a/lib/mix/lib/mix/tasks/deps.compile.ex b/lib/mix/lib/mix/tasks/deps.compile.ex
index 93d99373f2..1894532b37 100644
--- a/lib/mix/lib/mix/tasks/deps.compile.ex
+++ b/lib/mix/lib/mix/tasks/deps.compile.ex
@@ -265,7 +265,7 @@ defmodule Mix.Tasks.Deps.Compile do
     File.cd!(opts[:dest], fn ->
       env = [{"ERL_LIBS", Path.join(config[:env_path], "lib")}] ++ env
 
-      if Mix.Shell.cmd(command, env: env, into: %Mix.Shell{print_app?: print_app?}) != 0 do
+      if Mix.shell.cmd(command, env: env, print_app: print_app?) != 0 do
         Mix.raise(
           "Could not compile dependency #{inspect(app)}, \"#{command}\" command failed. " <>
             "You can recompile this dependency with \"mix deps.compile #{app}\", update it " <>
diff --git a/lib/mix/test/mix/rebar_test.exs b/lib/mix/test/mix/rebar_test.exs
index 25f73a27cf..6bec356162 100644
--- a/lib/mix/test/mix/rebar_test.exs
+++ b/lib/mix/test/mix/rebar_test.exs
@@ -202,8 +202,8 @@ defmodule Mix.RebarTest do
         assert_received {:mix_shell, :info, ["* Getting git_rebar" <> _]}
 
         Mix.Tasks.Deps.Compile.run([])
-        assert_received {:mix_shell, :write, ["===> Compiling git_rebar\n"]}
-        assert_received {:mix_shell, :write, ["===> Compiling rebar_dep\n"]}
+        assert_received {:mix_shell, :run, ["===> Compiling git_rebar\n"]}
+        assert_received {:mix_shell, :run, ["===> Compiling rebar_dep\n"]}
         assert :git_rebar.any_function() == :ok
         assert :rebar_dep.any_function() == :ok
 
@@ -233,8 +233,8 @@ defmodule Mix.RebarTest do
         assert_received {:mix_shell, :info, ["* Getting git_rebar " <> _]}
 
         Mix.Tasks.Deps.Compile.run([])
-        assert_received {:mix_shell, :write, ["===> Compiling git_rebar\n"]}
-        assert_received {:mix_shell, :write, ["===> Compiling rebar_dep\n"]}
+        assert_received {:mix_shell, :run, ["===> Compiling git_rebar\n"]}
+        assert_received {:mix_shell, :run, ["===> Compiling rebar_dep\n"]}
         assert :git_rebar.any_function() == :ok
         assert :rebar_dep.any_function() == :ok
 
diff --git a/lib/mix/test/mix/shell_test.exs b/lib/mix/test/mix/shell_test.exs
index 32ebf39c86..edb735b6b2 100644
--- a/lib/mix/test/mix/shell_test.exs
+++ b/lib/mix/test/mix/shell_test.exs
@@ -11,7 +11,7 @@ defmodule Mix.ShellTest do
     Mix.shell(Mix.Shell.IO)
 
     assert capture_io(fn ->
-             assert Mix.Shell.cmd("echo first && echo second", into: %Mix.Shell{}) == 0
+             assert Mix.shell.cmd("echo first && echo second") == 0
            end)
            |> String.replace(" \n", "\n") == "first\nsecond\n"
   after
diff --git a/lib/mix/test/mix/tasks/cmd_test.exs b/lib/mix/test/mix/tasks/cmd_test.exs
index 2b427300ad..fd1039746a 100644
--- a/lib/mix/test/mix/tasks/cmd_test.exs
+++ b/lib/mix/test/mix/tasks/cmd_test.exs
@@ -9,9 +9,9 @@ defmodule Mix.Tasks.CmdTest do
         Mix.Task.run("cmd", ["echo", "hello"])
         nl = os_newline()
         assert_received {:mix_shell, :info, ["==> bar"]}
-        assert_received {:mix_shell, :write, ["hello" <> ^nl]}
+        assert_received {:mix_shell, :run, ["hello" <> ^nl]}
         assert_received {:mix_shell, :info, ["==> foo"]}
-        assert_received {:mix_shell, :write, ["hello" <> ^nl]}
+        assert_received {:mix_shell, :run, ["hello" <> ^nl]}
       end)
     end
   end
@@ -22,9 +22,9 @@ defmodule Mix.Tasks.CmdTest do
         Mix.Task.run("cmd", ["--app", "bar", "echo", "hello"])
         nl = os_newline()
         assert_received {:mix_shell, :info, ["==> bar"]}
-        assert_received {:mix_shell, :write, ["hello" <> ^nl]}
+        assert_received {:mix_shell, :run, ["hello" <> ^nl]}
         refute_received {:mix_shell, :info, ["==> foo"]}
-        refute_received {:mix_shell, :write, ["hello" <> ^nl]}
+        refute_received {:mix_shell, :run, ["hello" <> ^nl]}
       end)
     end
   end