flagex

Extended flag parsing for Go. Reads command-line flags from configuration files, streams, and URLs on top of the standard flag package. This library does not try to reinvent flags. It just extends (not replaces) already existing flag package in standard library.

Usage

package main

import "flag"
import "github.com/pin2t/flagex"

var user    = flag.String("user", "", "user name")
var port    = flag.Int("port", 8080, "port number")
var url     = flag.String("url", "http://localhost", "URL")
var listen  = flag.String("listen", ":8080", "listen address")
var count   = flag.Int("count", 0, "count value")
var verbose = flag.Bool("verbose", false, "verbose mode")
var ratio   = flag.Float64("ratio", 1.0, "ratio value")
var conf    = flag.String("conf", "", "configuration file")

func main() {
    flag.Parse()
    if *conf != "" {
        flagex.ParseFile(*conf)
    }
    flagex.ParseURL("http://config-server/app.conf")
}

Format

Each line is name=value. Blank lines and lines starting with # are ignored. Flags already set on the command line take precedence.

File example

# app.conf
user=configuser
url=http://localhost:8332
listen=:9999
count=42
verbose=true
ratio=0.75

Environment variables example

With prefix APP_, environment variables map to flag names by stripping the prefix and converting to lowercase. For example, APP_URL sets the url flag.

export APP_USER=envuser
export APP_URL=http://env:9000
export APP_LISTEN=:8888
export APP_COUNT=99
export APP_VERBOSE=true
export APP_RATIO=1.5

Functions

• ParseFile(path) — reads configuration from a file.
• ParseStream(r) — reads configuration from an io.Reader.
• ParseURL(url) — fetches configuration via HTTP GET.
• ParseEnv(prefix) — fetches configuration from system environment variables.

FlagSet API

The FlagSet function wraps a flag.FlagSet so you can parse configuration into a non-default FlagSet (e.g., one created with flag.NewFlagSet).

package main

import "flag"
import "github.com/pin2t/flagex"

func main() {
    var fs = flag.NewFlagSet("myapp", flag.ExitOnError)
    var user = fs.String("user", "", "user name")
    var port = fs.Int("port", 8080, "port number")
    flagex.FlagSet(fs).ParseFile("app.conf")
    flagex.FlagSet(fs).ParseEnv("APP_")
    fmt.Println(*user, *port)
}

• FlagSet(fs).ParseFile(path) — reads configuration from a file.
• FlagSet(fs).ParseStream(r) — reads configuration from an io.Reader.
• FlagSet(fs).ParseURL(url) — fetches configuration via HTTP GET.
• FlagSet(fs).ParseEnv(prefix) — reads configuration from environment variables.

The package-level ParseFile, ParseStream, ParseURL, and ParseEnv functions are equivalent to calling the methods on FlagSet(flag.CommandLine).