Smarter behaviour when piping data in with one argument

cmd/evaluate_all_command.go

@@ -120,6 +120,10 @@ func evaluateAll(cmd *cobra.Command, args []string) (cmdError error) {
 	case 1:
 		if nullInput {
 			err = yqlib.NewStreamEvaluator().EvaluateNew(processExpression(args[0]), printer, "")
+		} else if pipingStdIn && args[0] != "-" {
+			// must have given a single expression and piping input from stdin
+			err = allAtOnceEvaluator.EvaluateFiles(processExpression(args[0]), []string{"-"}, printer, leadingContentPreProcessing, decoder)
+
 		} else {
 			err = allAtOnceEvaluator.EvaluateFiles(processExpression(""), []string{args[0]}, printer, leadingContentPreProcessing, decoder)
 		}

cmd/evalute_sequence_command.go

@@ -134,6 +134,9 @@ func evaluateSequence(cmd *cobra.Command, args []string) (cmdError error) {
 	case 1:
 		if nullInput {
 			err = streamEvaluator.EvaluateNew(processExpression(args[0]), printer, "")
+		} else if pipingStdIn && args[0] != "-" {
+			// must have given a single expression and piping input from stdin
+			err = streamEvaluator.EvaluateFiles(processExpression(args[0]), []string{"-"}, printer, leadingContentPreProcessing, decoder)
 		} else {
 			err = streamEvaluator.EvaluateFiles(processExpression(""), []string{args[0]}, printer, leadingContentPreProcessing, decoder)
 		}

cmd/root.go

@@ -14,13 +14,13 @@ func New() *cobra.Command {
 		Short: "yq is a lightweight and portable command-line YAML processor.",
 		Long: `yq is a portable command-line YAML processor (https://github.com/mikefarah/yq/) 
 See https://mikefarah.gitbook.io/yq/ for detailed documentation and examples.`,
+
 		RunE: func(cmd *cobra.Command, args []string) error {
 			if version {
 				cmd.Print(GetVersionDisplay())
 				return nil
 			}
-			cmd.Println(cmd.UsageString())
-			return nil
+			return evaluateSequence(cmd, args)
 
 		},
 		PersistentPreRun: func(cmd *cobra.Command, args []string) {