diff --git a/arguments.go b/arguments.go
index ed05256..7a768df 100644
--- a/arguments.go
+++ b/arguments.go
@@ -111,12 +111,21 @@ ENV:
         --max-stack <SIZE>       Jsonnet VM max stack size (default 500)
 
 EVAL:
-    -e, --eval <SNIPPET>         Process values with Jsonnet
+    <SCRIPT>                     Evaluate a Jsonnet script for each value.
+    -x, --exec <SCRIPT>          Same as above regardless of file extension.
+    -e, --eval <SNIPPET>         Evaluate a Jsonnet snippet for each value.
 
 
 If no INPUT is specified, values are read from stdin as YAML.
 If FILE is "-" or "" values are read from stdin until EOF.
-If FILE has no type option format is detected from extension.
+If FILE has no type option, format is detected from extension:
+    .json         -> JSON
+    .yaml, .yml   -> YAML
+    .jsonnet      -> Jsonnet script
+    .*            -> YCAT_FORMAT environment variable or YAML
+
+Default output format is YAML unless YCAT_OUTPUT environment variable is 'json'
+
 `
 
 var shortArgs = map[byte]string{
@@ -125,7 +134,8 @@ var shortArgs = map[byte]string{
 	'i': "import",
 	'v': "var",
 	'e': "eval",
-	'o': "output",
+	'x': "exec",
+	'o': "out",
 	'n': "null",
 	'a': "array",
 	'h': "help",
@@ -166,7 +176,10 @@ func (p *argParser) parseLong(name, value string, argv []string) ([]string, erro
 			return argv, err
 		}
 		p.addTask(p.eval.Snippet(filename, value))
-	case "output":
+	case "exec":
+		value, argv = shiftArgV(value, argv)
+		p.addFile(value, JSONNET)
+	case "out":
 		value, argv = shiftArgV(value, argv)
 		if p.output = OutputFromString(value); p.output == OutputInvalid {
 			return argv, fmt.Errorf("Invalid output format: %q", value)
@@ -271,6 +284,9 @@ func (p *argParser) addFile(path string, format Format) {
 }
 
 func (p *argParser) outputTask() (s StreamTask) {
+	if p.output == OutputInvalid {
+		p.output = DefaultOutput()
+	}
 	switch p.output {
 	case OutputJSON:
 		return StreamWriteJSON(p.stdout)
diff --git a/codec.go b/codec.go
index 3352361..16201cb 100644
--- a/codec.go
+++ b/codec.go
@@ -34,15 +34,56 @@ func FormatFromString(s string) Format {
 	}
 }
 
+// EnvDefaultFormat is the name of the env var for file format detection
+const EnvDefaultFormat = "YCAT_FORMAT"
+
+// EnvDefaultOutput is the name of the env var for default file output
+const EnvDefaultOutput = "YCAT_OUTPUT"
+
+var (
+	defaultFormat = Auto
+	defaultOutput = OutputInvalid
+)
+
+// DefaultFormat returns the default format from environment
+func DefaultFormat() Format {
+	if defaultFormat == Auto {
+		f := FormatFromString(os.Getenv(EnvDefaultFormat))
+		switch f {
+		case YAML, JSON:
+			defaultFormat = f
+		default:
+			defaultFormat = YAML
+		}
+	}
+	return defaultFormat
+}
+
+// DefaultOutput returns the default output from environment
+func DefaultOutput() Output {
+	if defaultOutput == OutputInvalid {
+		f := OutputFromString(os.Getenv(EnvDefaultOutput))
+		switch f {
+		case OutputYAML, OutputJSON:
+			defaultOutput = f
+		default:
+			defaultOutput = OutputYAML
+		}
+	}
+	return defaultOutput
+}
+
 // DetectFormat detects an input format from the extension
 func DetectFormat(filename string) Format {
 	switch path.Ext(filename) {
 	case ".json":
 		return JSON
-	case ".jsonnet", ".libsonnet":
+	case ".jsonnet":
 		return JSONNET
-	default:
+	case ".yaml", ".yml":
 		return YAML
+	default:
+		return DefaultFormat()
 	}
 }
 
@@ -51,10 +92,10 @@ type Output int
 
 // Output formats
 const (
-	OutputInvalid Output = iota - 1
+	OutputInvalid Output = iota
 	OutputYAML
 	OutputJSON
-	OutputRaw // Only with --eval
+	// OutputRaw // Only with --eval
 )
 
 // OutputFromString converts a string to Output
@@ -64,8 +105,8 @@ func OutputFromString(s string) Output {
 		return OutputJSON
 	case "yaml", "y":
 		return OutputYAML
-	case "raw", "r":
-		return OutputRaw
+	// case "raw", "r":
+	// 	return OutputRaw
 	default:
 		return OutputInvalid
 	}