From 66af38d4ca237cccc81aed901261ff2045acfac8 Mon Sep 17 00:00:00 2001
From: ryenus <ryenus@gmail.com>
Date: Thu, 2 Mar 2023 17:04:34 +0800
Subject: [PATCH] detect inputFormat from filename

---
 cmd/constant.go                 |  3 ++-
 cmd/evaluate_all_command.go     |  2 +-
 cmd/evalute_sequence_command.go |  2 +-
 cmd/root.go                     |  2 +-
 cmd/utils.go                    | 11 ++++++++++-
 pkg/yqlib/decoder.go            |  2 +-
 6 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/cmd/constant.go b/cmd/constant.go
index 573a72fb..daacf6fa 100644
--- a/cmd/constant.go
+++ b/cmd/constant.go
@@ -7,7 +7,8 @@ var unwrapScalar = false
 var writeInplace = false
 var outputToJSON = false
 var outputFormat = "yaml"
-var inputFormat = "yaml"
+var inputFormatDefault = "yaml"
+var inputFormat = "" // default to "" so that we can (lazily) detect inputFormat from input filename
 
 var exitStatus = false
 var forceColor = false
diff --git a/cmd/evaluate_all_command.go b/cmd/evaluate_all_command.go
index fff64fa5..d3589cb8 100644
--- a/cmd/evaluate_all_command.go
+++ b/cmd/evaluate_all_command.go
@@ -75,7 +75,7 @@ func evaluateAll(cmd *cobra.Command, args []string) (cmdError error) {
 		return err
 	}
 
-	decoder, err := configureDecoder(true)
+	decoder, err := configureDecoder(true, args[0])
 	if err != nil {
 		return err
 	}
diff --git a/cmd/evalute_sequence_command.go b/cmd/evalute_sequence_command.go
index dab803c3..94df3b56 100644
--- a/cmd/evalute_sequence_command.go
+++ b/cmd/evalute_sequence_command.go
@@ -100,7 +100,7 @@ func evaluateSequence(cmd *cobra.Command, args []string) (cmdError error) {
 
 	printer := yqlib.NewPrinter(encoder, printerWriter)
 
-	decoder, err := configureDecoder(false)
+	decoder, err := configureDecoder(false, args[0])
 	if err != nil {
 		return err
 	}
diff --git a/cmd/root.go b/cmd/root.go
index 97d9beaf..d832aca2 100644
--- a/cmd/root.go
+++ b/cmd/root.go
@@ -85,7 +85,7 @@ yq -P sample.json
 	}
 
 	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", "[yaml|y|props|p|xml|x] parse format for input. Note that json is a subset of yaml.")
+	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.") // use "" as default instead of "yaml", to be able to detect from input filename
 
 	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).")
diff --git a/cmd/utils.go b/cmd/utils.go
index 671dd86b..3da4de41 100644
--- a/cmd/utils.go
+++ b/cmd/utils.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"strings"
 
 	"github.com/mikefarah/yq/v4/pkg/yqlib"
 	"github.com/spf13/cobra"
@@ -56,7 +57,15 @@ func initCommand(cmd *cobra.Command, args []string) (string, []string, error) {
 	return expression, args, nil
 }
 
-func configureDecoder(evaluateTogether bool) (yqlib.Decoder, error) {
+func configureDecoder(evaluateTogether bool, inputFilename string) (yqlib.Decoder, error) {
+	if inputFormat == "" && inputFilename != "" {
+		nPos := strings.LastIndex(inputFilename, ".")
+		if nPos > -1 {
+			inputFormat = inputFilename[nPos+1:]
+		} else {
+			inputFormat = inputFormatDefault
+		}
+	}
 	yqlibInputFormat, err := yqlib.InputFormatFromString(inputFormat)
 	if err != nil {
 		return nil, err
diff --git a/pkg/yqlib/decoder.go b/pkg/yqlib/decoder.go
index ff7ab2db..dbc1d768 100644
--- a/pkg/yqlib/decoder.go
+++ b/pkg/yqlib/decoder.go
@@ -25,7 +25,7 @@ type Decoder interface {
 
 func InputFormatFromString(format string) (InputFormat, error) {
 	switch format {
-	case "yaml", "y":
+	case "yaml", "yml", "y":
 		return YamlInputFormat, nil
 	case "xml", "x":
 		return XMLInputFormat, nil