Added front-matter handler

cmd/constant.go

@@ -16,4 +16,7 @@ var verbose = false
 var version = false
 var prettyPrint = false
 
+// can be either "" (off), "extract" or "process"
+var frontMatter = ""
+
 var completedSuccessfully = false

cmd/evalute_sequence_command.go

@@ -103,6 +103,26 @@ func evaluateSequence(cmd *cobra.Command, args []string) error {
 		return errors.New("Cannot pass files in when using null-input flag")
 	}
 
+	if frontMatter != "" {
+		frontMatterHandler := yqlib.NewFrontMatterHandler(args[firstFileIndex])
+		err = frontMatterHandler.Split()
+		if err != nil {
+			return err
+		}
+		args[firstFileIndex] = frontMatterHandler.GetYamlFrontMatterFilename()
+
+		if frontMatter == "process" {
+			reader, err := os.Open(frontMatterHandler.GetContentFilename()) // #nosec
+			if err != nil {
+				return err
+			}
+			printer.SetAppendix(reader)
+			defer yqlib.SafelyCloseReader(reader)
+		}
+		defer frontMatterHandler.CleanUp()
+
+	}
+
 	switch len(args) {
 	case 0:
 		if pipingStdIn {

cmd/root.go

@@ -54,6 +54,7 @@ See https://mikefarah.gitbook.io/yq/ for detailed documentation and examples.`,
 
 	rootCmd.PersistentFlags().BoolVarP(&forceColor, "colors", "C", false, "force print with colors")
 	rootCmd.PersistentFlags().BoolVarP(&forceNoColor, "no-colors", "M", false, "force print with no colors")
+	rootCmd.PersistentFlags().StringVarP(&frontMatter, "front-matter", "f", "", "(extract|process) first input as yaml front-matter. Extract will pull out the yaml content, process will run the expression against the yaml content, leaving the remaining data in-tact")
 	rootCmd.AddCommand(
 		createEvaluateSequenceCommand(),
 		createEvaluateAllCommand(),