Argv

Parse string slices into structs

Usage scenario

argv attempts to parse a string slice, composed of parameters and values, and fill a struct based on its annotation information and converting values to the specific field type.

The typical use case is to convert an arbitrary list of arguments and values to a well-defined struct:

Sample main.go:

package main

import (
	"encoding/json"
	"errors"
	"fmt"
	"github.com/oddbit-project/argv"
	"os"
	"strings"
)

type CertInfo struct {
	CommonName         string `argv:"CN"`
	OrganizationalUnit string `argv:"OU"`
	Organization       string `argv:"O,optional"` // optional parameter
	Algorithm          string `argv:"alg"`
	KeyLen             uint   `argv:"bits"`
	Days               uint32 `argv:"days"`
}

func main() {
	if len(os.Args) < 2 {
		fmt.Printf("Usage: %s <command> [options]\n", os.Args[0])
		os.Exit(0)
	}
	cmd := os.Args[1]

	switch cmd {
	case "gencert":
		record := &CertInfo{}

		// attempt to parse & serialize values from command line
		err := argv.ParseArgv(record, os.Args[2:])
		if err == nil {
			str, _ := json.Marshal(record)
			fmt.Printf("Parsed parameters:\n %s\n", string(str))
			os.Exit(0)
		}

		// empty arg list, show available names
		if errors.Is(err, argv.ErrEmptyArgs) {
			names, err := argv.ParseNames(record)
			if err != nil {
				fmt.Println(err)
				os.Exit(-1)
			}
			fmt.Println("Available args: ", strings.Join(names, ", "))
			os.Exit(0)
		}

		fmt.Println(err)
		os.Exit(-1)
	default:
		fmt.Printf("'%s' is not a supported command\n", cmd)
		os.Exit(-1)
	}
}

Running:

$ go run main.go gencert
empty argument list
exit status 255

$ go run main.go gencert 
Available args:  CN, OU, O,optional, alg, bits, days

$ go run main.go gencert -CN "certificate name" -OU "SomeOrg"
value for arg 'alg' is missing
exit status 255

$  go run main.go gencert -CN "certificate name" -OU "SomeOrg" -alg "rsa" -bits 4096 -days 365
Parsed parameters:
 {"CommonName":"certificate name","OrganizationalUnit":"SomeOrg","Organization":"","Algorithm":"rsa","KeyLen":4096,"Days":365}

Supported field types

type	description
int	Int value
int8	Int8 value
int32	Int32 value
int64	Int64 value
uint	Uit value
uint8	Uint8 value
uint32	Uint32 value
uint64	Uint64 value
float32	float32 value; supports scientific notation
float64	float64 value; supports scientific notation
time.Time	RFC3339 time string
bool	true/false or 1/0 string
string	arbitrary string
[]string	list of strings, such as "value1,value2"