Auto output format (#1599)

* Use file extension to auto detect output format!

* Use file extension to auto detect output format!

* formatting

cmd/constant.go

@@ -6,8 +6,9 @@ var unwrapScalar = false
 
 var writeInplace = false
 var outputToJSON = false
-var outputFormat = "yaml"
-var inputFormatDefault = "yaml"
+
+var outputFormat = ""
+
 var inputFormat = ""
 
 var exitStatus = false

cmd/evaluate_all_command.go

@@ -75,12 +75,7 @@ func evaluateAll(cmd *cobra.Command, args []string) (cmdError error) {
 		return err
 	}
 
-	inputFilename := ""
-	if len(args) > 0 {
-		inputFilename = args[0]
-	}
-
-	decoder, err := configureDecoder(true, inputFilename)
+	decoder, err := configureDecoder(true)
 	if err != nil {
 		return err
 	}

cmd/evalute_sequence_command.go

@@ -100,12 +100,7 @@ func evaluateSequence(cmd *cobra.Command, args []string) (cmdError error) {
 
 	printer := yqlib.NewPrinter(encoder, printerWriter)
 
-	inputFilename := ""
-	if len(args) > 0 {
-		inputFilename = args[0]
-	}
-
-	decoder, err := configureDecoder(false, inputFilename)
+	decoder, err := configureDecoder(false)
 	if err != nil {
 		return err
 	}

cmd/root.go

@@ -53,25 +53,6 @@ yq -P sample.json
 			logging.SetBackend(backend)
 			yqlib.InitExpressionParser()
 
-			outputFormatType, err := yqlib.OutputFormatFromString(outputFormat)
-
-			if err != nil {
-				return err
-			}
-
-			if outputFormatType == yqlib.YamlOutputFormat ||
-				outputFormatType == yqlib.PropsOutputFormat {
-				unwrapScalar = true
-			}
-			if unwrapScalarFlag.IsExplicitySet() {
-				unwrapScalar = unwrapScalarFlag.IsSet()
-			}
-
-			//copy preference form global setting
-			yqlib.ConfiguredYamlPreferences.UnwrapScalar = unwrapScalar
-
-			yqlib.ConfiguredYamlPreferences.PrintDocSeparators = !noDocSeparators
-
 			return nil
 		},
 	}
@@ -84,8 +65,8 @@ yq -P sample.json
 		panic(err)
 	}
 
-	rootCmd.PersistentFlags().StringVarP(&outputFormat, "output-format", "o", "yaml", "[yaml|y|json|j|props|p|xml|x] output format type.")
-	rootCmd.PersistentFlags().StringVarP(&inputFormat, "input-format", "p", "", "[yaml|y|props|p|xml|x] parse format for input. Note that json is a subset of yaml.")
+	rootCmd.PersistentFlags().StringVarP(&outputFormat, "output-format", "o", "auto", "[auto|a|yaml|y|json|j|props|p|xml|x] output format type.")
+	rootCmd.PersistentFlags().StringVarP(&inputFormat, "input-format", "p", "auto", "[auto|a|yaml|y|props|p|xml|x] parse format for input. Note that json is a subset of yaml.")
 
 	rootCmd.PersistentFlags().StringVar(&yqlib.ConfiguredXMLPreferences.AttributePrefix, "xml-attribute-prefix", yqlib.ConfiguredXMLPreferences.AttributePrefix, "prefix for xml attributes")
 	rootCmd.PersistentFlags().StringVar(&yqlib.ConfiguredXMLPreferences.ContentName, "xml-content-name", yqlib.ConfiguredXMLPreferences.ContentName, "name for xml content (if no attribute name is present).")

cmd/utils.go

@@ -53,15 +53,52 @@ func initCommand(cmd *cobra.Command, args []string) (string, []string, error) {
 		return "", nil, fmt.Errorf("cannot pass files in when using null-input flag")
 	}
 
+	inputFilename := ""
+	if len(args) > 0 {
+		inputFilename = args[0]
+	}
+	if inputFormat == "" || inputFormat == "auto" || inputFormat == "a" {
+
+		inputFormat = yqlib.FormatFromFilename(inputFilename)
+		if outputFormat == "" || outputFormat == "auto" || outputFormat == "a" {
+			outputFormat = yqlib.FormatFromFilename(inputFilename)
+		}
+	} else if outputFormat == "" || outputFormat == "auto" || outputFormat == "a" {
+		// backwards compatibility -
+		// before this was introduced, `yq -pcsv things.csv`
+		// would produce *yaml* output.
+		//
+		outputFormat = yqlib.FormatFromFilename(inputFilename)
+		if inputFilename != "-" {
+			yqlib.GetLogger().Warning("yq default output is now 'auto' (based on the filename extension). Normally yq would output '%v', but for backwards compatibility 'yaml' has been set. Please use -oy to specify yaml, or drop the -p flag.", outputFormat)
+		}
+		outputFormat = "yaml"
+	}
+
+	outputFormatType, err := yqlib.OutputFormatFromString(outputFormat)
+
+	if err != nil {
+		return "", nil, err
+	}
+	yqlib.GetLogger().Debug("Using outputformat %v", outputFormat)
+
+	if outputFormatType == yqlib.YamlOutputFormat ||
+		outputFormatType == yqlib.PropsOutputFormat {
+		unwrapScalar = true
+	}
+	if unwrapScalarFlag.IsExplicitySet() {
+		unwrapScalar = unwrapScalarFlag.IsSet()
+	}
+
+	//copy preference form global setting
+	yqlib.ConfiguredYamlPreferences.UnwrapScalar = unwrapScalar
+
+	yqlib.ConfiguredYamlPreferences.PrintDocSeparators = !noDocSeparators
+
 	return expression, args, nil
 }
 
-func configureDecoder(evaluateTogether bool, inputFilename string) (yqlib.Decoder, error) {
-	if inputFormat == "" {
-		inputFormat = yqlib.InputFormatFromFilename(inputFilename, inputFormatDefault)
-	} else {
-		yqlib.GetLogger().Debugf("user specified inputFormat '%s'", inputFormat)
-	}
+func configureDecoder(evaluateTogether bool) (yqlib.Decoder, error) {
 	yqlibInputFormat, err := yqlib.InputFormatFromString(inputFormat)
 	if err != nil {
 		return nil, err