diff --git a/main.go b/main.go
index 90a0445..352d497 100644
--- a/main.go
+++ b/main.go
@@ -135,16 +135,16 @@ func walk(ch chan<- *file, start string) {
 func addLicense(path string, fmode os.FileMode, tmpl *template.Template, data *copyrightData) error {
 	var lic []byte
 	var err error
-	switch filepath.Ext(path) {
+	switch fileExtension(path) {
 	default:
 		return nil
 	case ".c", ".h":
 		lic, err = prefix(tmpl, data, "/*", " * ", " */")
 	case ".js", ".jsx", ".tsx", ".css", ".tf":
 		lic, err = prefix(tmpl, data, "/**", " * ", " */")
-	case ".cc", ".cpp", ".cs", ".go", ".hh", ".hpp", ".java", ".m", ".mm", ".proto", ".rs", ".scala", ".swift", ".dart":
+	case ".cc", ".cpp", ".cs", ".go", ".hh", ".hpp", ".java", ".m", ".mm", ".proto", ".rs", ".scala", ".swift", ".dart", ".groovy":
 		lic, err = prefix(tmpl, data, "", "// ", "")
-	case ".py", ".sh", ".yaml", ".yml":
+	case ".py", ".sh", ".yaml", ".yml", ".dockerfile", "dockerfile", ".rb", "gemfile":
 		lic, err = prefix(tmpl, data, "", "# ", "")
 	case ".el", ".lisp":
 		lic, err = prefix(tmpl, data, "", ";; ", "")
@@ -178,10 +178,19 @@ func addLicense(path string, fmode os.FileMode, tmpl *template.Template, data *c
 	return ioutil.WriteFile(path, b, fmode)
 }
 
+func fileExtension(name string) string {
+	if v := filepath.Ext(name); v != "" {
+		return strings.ToLower(v)
+	}
+	return strings.ToLower(filepath.Base(name))
+}
+
 var head = []string{
-	"#!",        // shell script
-	"<?xml",     // XML declaratioon
-	"<!doctype", // HTML doctype
+	"#!",                       // shell script
+	"<?xml",                    // XML declaratioon
+	"<!doctype",                // HTML doctype
+	"# encoding:",              // Ruby encoding
+	"# frozen_string_literal:", // Ruby interpreter instruction
 }
 
 func hashBang(b []byte) []byte {
diff --git a/testdata/expected/Gemfile b/testdata/expected/Gemfile
new file mode 100644
index 0000000..919c8b1
--- /dev/null
+++ b/testdata/expected/Gemfile
@@ -0,0 +1,15 @@
+# Copyright 2016 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+puts "Hello world!"
diff --git a/testdata/expected/file.Dockerfile b/testdata/expected/file.Dockerfile
new file mode 100644
index 0000000..e08f020
--- /dev/null
+++ b/testdata/expected/file.Dockerfile
@@ -0,0 +1,16 @@
+# Copyright 2016 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+FROM scratch
+CMD ["echo", "hello world"]
diff --git a/testdata/expected/file.groovy b/testdata/expected/file.groovy
new file mode 100644
index 0000000..0bec985
--- /dev/null
+++ b/testdata/expected/file.groovy
@@ -0,0 +1,17 @@
+// Copyright 2016 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+def dummy_function() {
+    println "Hello world"
+}
diff --git a/testdata/expected/file.rb b/testdata/expected/file.rb
new file mode 100644
index 0000000..85b433b
--- /dev/null
+++ b/testdata/expected/file.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+# Copyright 2016 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+puts "Hello world!"
diff --git a/testdata/initial/Gemfile b/testdata/initial/Gemfile
new file mode 100644
index 0000000..08b85bf
--- /dev/null
+++ b/testdata/initial/Gemfile
@@ -0,0 +1 @@
+puts "Hello world!"
diff --git a/testdata/initial/file.Dockerfile b/testdata/initial/file.Dockerfile
new file mode 100644
index 0000000..eb8b2ad
--- /dev/null
+++ b/testdata/initial/file.Dockerfile
@@ -0,0 +1,2 @@
+FROM scratch
+CMD ["echo", "hello world"]
diff --git a/testdata/initial/file.groovy b/testdata/initial/file.groovy
new file mode 100644
index 0000000..3434ffa
--- /dev/null
+++ b/testdata/initial/file.groovy
@@ -0,0 +1,3 @@
+def dummy_function() {
+    println "Hello world"
+}
diff --git a/testdata/initial/file.rb b/testdata/initial/file.rb
new file mode 100644
index 0000000..de437c6
--- /dev/null
+++ b/testdata/initial/file.rb
@@ -0,0 +1,2 @@
+# frozen_string_literal: true
+puts "Hello world!"