Docker run -e FOO should erase FOO if FOO isn't set in client env

See #10141 for more info, but the main point of this is to make sure
that if you do "docker run -e FOO ..." that FOO from the current env
is passed into the container.  This means that if there's a value, its
set.  But it also means that if FOO isn't set then it should be unset in
the container too - even if it has to remove it from the env.  So,
   unset HOSTNAME
   docker run -e HOSTNAME busybox env
should _NOT_ show HOSTNAME in the list at all

Closes #10141

Signed-off-by: Doug Davis <dug@us.ibm.com>

docs/sources/reference/commandline/cli.md

@@ -1725,9 +1725,12 @@ 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

integration-cli/docker_cli_run_test.go

@@ -795,10 +795,7 @@ 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{
@@ -826,6 +823,72 @@ 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 {

opts/opts.go

@@ -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
 }
 

utils/utils.go

@@ -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) {