@@ -1736,9 +1736,12 @@ ports in Docker.

 This sets environmental variables in the container. For illustration all three

 flags are shown here. Where `-e`, `--env` take an environment variable and

-value, or if no "=" is provided, then that variable's current value is passed

-through (i.e. `$MYVAR1` from the host is set to `$MYVAR1` in the container). All

-three flags, `-e`, `--env` and `--env-file` can be repeated.

+value, or if no `=` is provided, then that variable's current value is passed

+through (i.e. `$MYVAR1` from the host is set to `$MYVAR1` in the container). 

+When no `=` is provided and that variable is not defined in the client's

+environment then that variable will be removed from the container's list of

+environment variables.

+All three flags, `-e`, `--env` and `--env-file` can be repeated.

 Regardless of the order of these three flags, the `--env-file` are processed

 first, and then `-e`, `--env` flags. This way, the `-e` or `--env` will

@@ -792,10 +792,7 @@ func TestRunEnvironment(t *testing.T) {

 		t.Fatal(err, out)

 	}

-	actualEnv := strings.Split(out, "\n")

-	if actualEnv[len(actualEnv)-1] == "" {

-		actualEnv = actualEnv[:len(actualEnv)-1]

-	}

+	actualEnv := strings.Split(strings.TrimSpace(out), "\n")

 	sort.Strings(actualEnv)

 	goodEnv := []string{

@@ -823,6 +820,72 @@ func TestRunEnvironment(t *testing.T) {

 	logDone("run - verify environment")

 }

+func TestRunEnvironmentErase(t *testing.T) {

+	// Test to make sure that when we use -e on env vars that are

+	// not set in our local env that they're removed (if present) in

+	// the container

+	cmd := exec.Command(dockerBinary, "run", "-e", "FOO", "-e", "HOSTNAME", "busybox", "env")

+	cmd.Env = []string{}

+	out, _, err := runCommandWithOutput(cmd)

+	if err != nil {

+		t.Fatal(err, out)

+	}

+

+	actualEnv := strings.Split(strings.TrimSpace(out), "\n")

+	sort.Strings(actualEnv)

+

+	goodEnv := []string{

+		"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",

+		"HOME=/root",

+	}

+	sort.Strings(goodEnv)

+	if len(goodEnv) != len(actualEnv) {

+		t.Fatalf("Wrong environment: should be %d variables, not: %q\n", len(goodEnv), strings.Join(actualEnv, ", "))

+	}

+	for i := range goodEnv {

+		if actualEnv[i] != goodEnv[i] {

+			t.Fatalf("Wrong environment variable: should be %s, not %s", goodEnv[i], actualEnv[i])

+		}

+	}

+

+	deleteAllContainers()

+

+	logDone("run - verify environment erase")

+}

+

+func TestRunEnvironmentOverride(t *testing.T) {

+	// Test to make sure that when we use -e on env vars that are

+	// already in the env that we're overriding them

+	cmd := exec.Command(dockerBinary, "run", "-e", "HOSTNAME", "-e", "HOME=/root2", "busybox", "env")

+	cmd.Env = []string{"HOSTNAME=bar"}

+	out, _, err := runCommandWithOutput(cmd)

+	if err != nil {

+		t.Fatal(err, out)

+	}

+

+	actualEnv := strings.Split(strings.TrimSpace(out), "\n")

+	sort.Strings(actualEnv)

+

+	goodEnv := []string{

+		"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",

+		"HOME=/root2",

+		"HOSTNAME=bar",

+	}

+	sort.Strings(goodEnv)

+	if len(goodEnv) != len(actualEnv) {

+		t.Fatalf("Wrong environment: should be %d variables, not: %q\n", len(goodEnv), strings.Join(actualEnv, ", "))

+	}

+	for i := range goodEnv {

+		if actualEnv[i] != goodEnv[i] {

+			t.Fatalf("Wrong environment variable: should be %s, not %s", goodEnv[i], actualEnv[i])

+		}

+	}

+

+	deleteAllContainers()

+

+	logDone("run - verify environment override")

+}

+

 func TestRunContainerNetwork(t *testing.T) {

 	cmd := exec.Command(dockerBinary, "run", "busybox", "ping", "-c", "1", "127.0.0.1")

 	if _, err := runCommand(cmd); err != nil {

@@ -11,6 +11,7 @@ import (

 	"github.com/docker/docker/api"

 	flag "github.com/docker/docker/pkg/mflag"

 	"github.com/docker/docker/pkg/parsers"

+	"github.com/docker/docker/utils"

 )

 var (

@@ -168,6 +169,9 @@ func ValidateEnv(val string) (string, error) {

 	if len(arr) > 1 {

 		return val, nil

 	}

+	if !utils.DoesEnvExist(val) {

+		return val, nil

+	}

 	return fmt.Sprintf("%s=%s", val, os.Getenv(val)), nil

 }

@@ -401,7 +401,17 @@ func ReplaceOrAppendEnvValues(defaults, overrides []string) []string {

 		parts := strings.SplitN(e, "=", 2)

 		cache[parts[0]] = i

 	}

+

 	for _, value := range overrides {

+		// Values w/o = means they want this env to be removed/unset.

+		if !strings.Contains(value, "=") {

+			if i, exists := cache[value]; exists {

+				defaults[i] = "" // Used to indicate it should be removed

+			}

+			continue

+		}

+

+		// Just do a normal set/update

 		parts := strings.SplitN(value, "=", 2)

 		if i, exists := cache[parts[0]]; exists {

 			defaults[i] = value

@@ -409,9 +419,28 @@ func ReplaceOrAppendEnvValues(defaults, overrides []string) []string {

 			defaults = append(defaults, value)

 		}

 	}

+

+	// Now remove all entries that we want to "unset"

+	for i := 0; i < len(defaults); i++ {

+		if defaults[i] == "" {

+			defaults = append(defaults[:i], defaults[i+1:]...)

+			i--

+		}

+	}

+

 	return defaults

 }

+func DoesEnvExist(name string) bool {

+	for _, entry := range os.Environ() {

+		parts := strings.SplitN(entry, "=", 2)

+		if parts[0] == name {

+			return true

+		}

+	}

+	return false

+}

+

 // ReadSymlinkedDirectory returns the target directory of a symlink.

 // The target of the symbolic link may not be a file.

 func ReadSymlinkedDirectory(path string) (string, error) {