configurable docker command via env vars

src/main/java/org/jenkinsci/plugins/docker/workflow/WithContainerStep.java

@@ -196,10 +196,10 @@ public Execution() {
                 volumes.put(tmp, tmp);
             }
 
-            String command = launcher.isUnix() ? "cat" : "cmd.exe";
+            String[] command = launcher.isUnix() ? DockerClient.getUnixCommand(envHost, "cat") : "cmd.exe".split(" ");
             container = dockerClient.run(env, step.image, step.args, ws, volumes, volumesFromContainers, envReduced, dockerClient.whoAmI(), /* expected to hang until killed */ command);
             final List<String> ps = dockerClient.listProcess(env, container);
-            if (!ps.contains(command)) {
+            if (!ps.contains(Arrays.toString(command))) {
                 listener.error(
                     "The container started but didn't run the expected command. " +
                         "Please double check your ENTRYPOINT does execute the command passed as docker run argument, " +

src/main/java/org/jenkinsci/plugins/docker/workflow/client/DockerClient.java

@@ -90,6 +90,10 @@ public class DockerClient {
     private final @CheckForNull Node node;
     private final @CheckForNull String toolName;
 
+    public static String[] getUnixCommand(EnvVars env, String defaultCmd) {
+        return env.get("DEFAULT_DOCKER_COMMAND", defaultCmd).split(" ");
+    }
+
     public DockerClient(@NonNull Launcher launcher, @CheckForNull Node node, @CheckForNull String toolName) {
         this.launcher = launcher;
         this.node = node;

src/test/java/org/jenkinsci/plugins/docker/workflow/DockerTestUtil.java

@@ -84,6 +84,11 @@ public static EnvVars newDockerLaunchEnv() {
         return env;
     }
 
+    public static EnvVars newHostEnv() {
+        EnvVars env = new EnvVars();
+        env.put("DEFAULT_DOCKER_COMMAND", "sh -c sleep INF");
+        return env;
+    }
+
     private DockerTestUtil() {}
-
 }

src/test/java/org/jenkinsci/plugins/docker/workflow/client/DockerClientTest.java

@@ -58,9 +58,10 @@ public void setup() throws Exception {
     @Test
     public void test_run() throws IOException, InterruptedException {
         EnvVars launchEnv = DockerTestUtil.newDockerLaunchEnv();
+        String[] defaultCommand = DockerClient.getUnixCommand(DockerTestUtil.newHostEnv(), "cat");
         String containerId =
                 dockerClient.run(launchEnv, "learn/tutorial", null, null, Collections.<String, String>emptyMap(), Collections.<String>emptyList(), new EnvVars(),
-                        dockerClient.whoAmI(), "cat");
+                        dockerClient.whoAmI(), defaultCommand);
         Assert.assertEquals(64, containerId.length());
         ContainerRecord containerRecord = dockerClient.getContainerRecord(launchEnv, containerId);
         Assert.assertEquals(dockerClient.inspect(launchEnv, "learn/tutorial", ".Id"), containerRecord.getImageId());