Each configurable option should exist in three forms:
- Struct field (PascalCase)
- CLI flag (--kebab-case)
- Environment variable (SCREAMING_SNAKE_CASE)
Keeping the three in sync is tedious and error-prone.
This package uses a struct as the source of truth to generate urfave/cli/v2
flags with consistent naming conventions.
package main
import (
"log"
"os"
"github.com/sebnyberg/flagtags"
"github.com/urfave/cli/v2"
)
type config struct {
Port int `value:"3001"`
DisableAuth bool
JWTSignKey string
}
func main() {
var opts flagtags.Options
opts.EnvPrefix = "MYAPP_"
flags := flagtags.ParseFlagsWithOpts(&config, opts)
app := &cli.App{flags: flags}
app.Run(os.Args)
}| Tag | Flag field | Description | Default value |
|---|---|---|---|
name |
flag.Name |
Flag name | Struct field name in kebab-case |
env |
flag.EnvVars[0] |
Environment variable name | Struct field name in SCREAMING_SNAKE_CASE |
value |
flag.Value |
Default flag value | Default initialized value for the corresponding primitive type |
usage |
flag.Usage |
Usage | Empty string |
Currently this library only supports struct fields of type:
intstringbool
package main
import (
"fmt"
"os"
"github.com/kr/pretty"
"github.com/sebnyberg/flagtags"
"github.com/urfave/cli/v2"
)
type config struct {
Port int `value:"3001"`
DisableAuth bool `usage:"Disable authentication"`
JWTSignKey string `usage:"JWT signing key"`
DatabaseHost string `name:"pghost" env:"PGHOST" usage:"Postgres hostname"`
DatabasePassword string `name:"pgpassword" env:"PGPASSWORD" usage:"Postgres hostname"`
}
func main() {
var conf config
var parseOpts flagtags.Options
parseOpts.EnvPrefix = "MYAPP_"
flags := flagtags.MustParseFlagsWithOpts(&conf, parseOpts)
app := &cli.App{
Name: "server",
HelpName: "server",
Usage: "run the server",
Flags: flags,
Action: func(c *cli.Context) error {
pretty.Println(conf)
return nil
},
}
if err := app.Run(os.Args); err != nil {
fmt.Println(err)
os.Exit(1)
}
}Example output from the CLI invocation:
$ go run main.go --help
NAME:
server - run the server
USAGE:
server [global options] command [command options] [arguments...]
COMMANDS:
help, h Shows a list of commands or help for one command
GLOBAL OPTIONS:
--port value (default: 3001) [$PORT]
--disable-auth Disable authentication (default: false) [$DISABLE_AUTH]
--jwt-sign-key value JWT signing key [$JWT_SIGN_KEY]
--pghost value Postgres hostname (default: "test") [$PGHOST]
--pgpassword value Postgres hostname [$PGPASSWORD]
--help, -h show help (default: false)