scan_value.go

package main

import (
	"bufio"
	"bytes"
	"encoding/json"
	"fmt"
	"os"

	log "github.com/sirupsen/logrus"
)

func ScanValue(s string, format string) (interface{}, error) {
	c := format[len(format)-1:]
	switch c {
	case "s", "c", "q":
		var v string
		fmt.Sscanf(s, format, &v)
		return v, nil
	case "d", "b", "o", "X", "x", "U":
		var v int64
		fmt.Sscanf(s, format, &v)
		return v, nil
	case "e", "E", "f", "g", "G":
		var v float64
		fmt.Sscanf(s, format, &v)
		return v, nil
	case "t":
		var v bool
		fmt.Sscanf(s, format, &v)
		return v, nil
	default:
		return nil, fmt.Errorf("invalid format: %s", c)
	}

}

func JsonStringify(v interface{}) string {
	bs := new(bytes.Buffer)
	err := json.NewEncoder(bs).Encode(v)
	if err != nil {
		panic(err)
	}
	return bs.String()
}

func main() {
	inputFormat := "%s"
	outputFormat := "json"
	switch len(os.Args) {
	case 0, 1:
		break
	case 2:
		inputFormat = os.Args[1]
	case 3:
		inputFormat = os.Args[1]
		outputFormat = os.Args[2]
	default:
		log.Fatalf("invalid arguments: %v", os.Args[3:])
	}
	scanner := bufio.NewScanner(os.Stdin)
	for scanner.Scan() {
		l := scanner.Text()
		v, err := ScanValue(l, inputFormat)
		if err != nil {
			log.Error(err)
			continue
		}
		if outputFormat == "json" {
			fmt.Print(JsonStringify(v))
		} else {
			fmt.Printf(outputFormat+"\n", v)
		}
	}
	if err := scanner.Err(); err != nil {
		log.Fatal(err)
	}
}