diff --git a/common/src/main/java/org/implab/gradle/common/dsl/CommandSpec.java b/common/src/main/java/org/implab/gradle/common/dsl/TaskCommandSpecMixin.java
rename from common/src/main/java/org/implab/gradle/common/dsl/CommandSpec.java
rename to common/src/main/java/org/implab/gradle/common/dsl/TaskCommandSpecMixin.java
--- a/common/src/main/java/org/implab/gradle/common/dsl/CommandSpec.java
+++ b/common/src/main/java/org/implab/gradle/common/dsl/TaskCommandSpecMixin.java
@@ -3,7 +3,7 @@ package org.implab.gradle.common.dsl;
 
 import org.gradle.api.provider.ListProperty;
 
-public interface CommandSpec {
+public interface TaskCommandSpecMixin {
     ListProperty<String> getCommandLine();
 
     void commandLine(Object arg0, Object... args);
diff --git a/common/src/main/java/org/implab/gradle/common/dsl/TaskDependency.java b/common/src/main/java/org/implab/gradle/common/dsl/TaskDependency.java
deleted file mode 100644
--- a/common/src/main/java/org/implab/gradle/common/dsl/TaskDependency.java
+++ /dev/null
@@ -1,22 +0,0 @@
-package org.implab.gradle.common.dsl;
-
-import org.gradle.api.Buildable;
-import org.gradle.api.tasks.TaskProvider;
-
-public interface TaskDependency {
-
-    Object reference();
-
-    public static TaskDependency named(String name) {
-        return () -> name;
-    }
-
-    public static TaskDependency provider(TaskProvider<?> provider) {
-        return () -> provider;
-    }
-
-    public static TaskDependency buildable(Buildable dependency) {
-        return () -> dependency;
-    }
-
-}
diff --git a/common/src/main/java/org/implab/gradle/common/dsl/EnvironmentSpec.java b/common/src/main/java/org/implab/gradle/common/dsl/TaskEnvSpecMixin.java
rename from common/src/main/java/org/implab/gradle/common/dsl/EnvironmentSpec.java
rename to common/src/main/java/org/implab/gradle/common/dsl/TaskEnvSpecMixin.java
--- a/common/src/main/java/org/implab/gradle/common/dsl/EnvironmentSpec.java
+++ b/common/src/main/java/org/implab/gradle/common/dsl/TaskEnvSpecMixin.java
@@ -6,6 +6,7 @@ import java.util.Map;
 import org.gradle.api.Action;
 import org.gradle.api.file.DirectoryProperty;
 import org.gradle.api.provider.MapProperty;
+import org.gradle.api.provider.Property;
 import org.implab.gradle.common.utils.Closures;
 import org.implab.gradle.common.utils.Values;
 
@@ -16,7 +17,10 @@ import groovy.lang.Closure;
  * working directory and environment variables for the processes started within
  * this shell.
  */
-public interface EnvironmentSpec {
+public interface TaskEnvSpecMixin {
+
+    /** Inherit environment from current process */
+    Property<Boolean> getInheritEnvironment();
 
     /** Working directory */
     DirectoryProperty getWorkingDirectory();
diff --git a/common/src/main/java/org/implab/gradle/common/dsl/PipeSpec.java b/common/src/main/java/org/implab/gradle/common/dsl/TaskPipeSpecMixin.java
rename from common/src/main/java/org/implab/gradle/common/dsl/PipeSpec.java
rename to common/src/main/java/org/implab/gradle/common/dsl/TaskPipeSpecMixin.java
--- a/common/src/main/java/org/implab/gradle/common/dsl/PipeSpec.java
+++ b/common/src/main/java/org/implab/gradle/common/dsl/TaskPipeSpecMixin.java
@@ -3,7 +3,7 @@ package org.implab.gradle.common.dsl;
 import org.eclipse.jdt.annotation.NonNullByDefault;
 
 @NonNullByDefault
-public interface PipeSpec {
+public interface TaskPipeSpecMixin {
     RedirectToSpec getStdout();
 
     RedirectToSpec getStderr();
diff --git a/common/src/main/java/org/implab/gradle/common/tasks/ShellExecTask.java b/common/src/main/java/org/implab/gradle/common/tasks/ShellExecTask.java
--- a/common/src/main/java/org/implab/gradle/common/tasks/ShellExecTask.java
+++ b/common/src/main/java/org/implab/gradle/common/tasks/ShellExecTask.java
@@ -9,13 +9,14 @@ import org.gradle.api.DefaultTask;
 import org.gradle.api.file.DirectoryProperty;
 import org.gradle.api.provider.ListProperty;
 import org.gradle.api.provider.MapProperty;
+import org.gradle.api.provider.Property;
 import org.gradle.api.tasks.Internal;
 import org.gradle.api.tasks.TaskAction;
-import org.implab.gradle.common.dsl.CommandSpec;
-import org.implab.gradle.common.dsl.PipeSpec;
+import org.implab.gradle.common.dsl.TaskCommandSpecMixin;
+import org.implab.gradle.common.dsl.TaskPipeSpecMixin;
 import org.implab.gradle.common.dsl.RedirectFromSpec;
 import org.implab.gradle.common.dsl.RedirectToSpec;
-import org.implab.gradle.common.dsl.EnvironmentSpec;
+import org.implab.gradle.common.dsl.TaskEnvSpecMixin;
 import org.implab.gradle.common.exec.ExecBuilder;
 import org.implab.gradle.common.utils.ObjectsMixin;
 import org.implab.gradle.common.utils.Strings;
@@ -23,7 +24,7 @@ import org.implab.gradle.common.utils.Th
 
 public abstract class ShellExecTask
         extends DefaultTask
-        implements CommandSpec, PipeSpec, EnvironmentSpec, ObjectsMixin {
+        implements TaskCommandSpecMixin, TaskPipeSpecMixin, TaskEnvSpecMixin, ObjectsMixin {
 
     private final RedirectToSpec redirectStderr = new RedirectToSpec();
 
@@ -33,6 +34,10 @@ public abstract class ShellExecTask
 
     @Internal
     @Override
+    public abstract Property<Boolean> getInheritEnvironment();
+
+    @Internal
+    @Override
     public abstract DirectoryProperty getWorkingDirectory();
 
     @Internal
diff --git a/common/src/main/java/org/implab/gradle/common/utils/Closures.java b/common/src/main/java/org/implab/gradle/common/utils/Closures.java
--- a/common/src/main/java/org/implab/gradle/common/utils/Closures.java
+++ b/common/src/main/java/org/implab/gradle/common/utils/Closures.java
@@ -11,10 +11,7 @@ public final class Closures {
     }
 
     public static <T> Action<T> action(Closure<?> closure) {
-        return arg -> {
-            closure.setDelegate(arg);
-            closure.call(arg);
-        };
+        return arg -> apply(closure, arg);
     }
 
     public static void apply(Closure<?> action, Object target) {
diff --git a/common/src/main/java/org/implab/gradle/common/utils/Values.java b/common/src/main/java/org/implab/gradle/common/utils/Values.java
--- a/common/src/main/java/org/implab/gradle/common/utils/Values.java
+++ b/common/src/main/java/org/implab/gradle/common/utils/Values.java
@@ -66,6 +66,10 @@ public final class Values {
         return () -> new ArrayIterator<>(values);
     }
 
+    public static <T> Optional<T> optional(Provider<T> provider) {
+        return provider.isPresent() ? Optional.of(provider.get()) : Optional.empty();
+    }
+
     private static class ArrayIterator<T> implements Iterator<T> {
         private final T[] data;