envflag

Documentation

Overview

Package envflag implements support for setting flags through environment variables. Unlike the package standard flag package, a set of top-level wrapper functions are not provided.

Example

package main

import (
	"flag"
	"fmt"

	"github.com/LiveRamp/gazette/pkg/envflag"
)

func main() {
	// Define envflags. Because this example is testable, long descriptive
	// names have been chosen to reduce the chances of an environment variable
	// by that name actually existing.
	dbEndpoint := envflag.CommandLine.String(
		"envflagExampleMysql", "MYSQL_SERVICE_ENDPOINT_EXAMPLE", "mysql.example:3306", "MySQL endpoint")
	redisEndpoint := envflag.CommandLine.String(
		"envflagExampleRedis", "REDIS_SERVICE_ENDPOINT_EXAMPLE", "redis.example:6379", "Redis endpoint")
	pingURL := envflag.CommandLine.String(
		"ping", "ENVFLAG_EXAMPLE_PING_URL", "http://localhost/ping", "URL to ping")
	user := envflag.CommandLine.String(
		"user", "ENVFLAG_EXAMPLE_USER", "nobody", "User to act as")

	// Parse values from the environment. This is typically done before parsing
	// from the command-line arguments so the command-line takes precedence
	// over the environment.
	envflag.CommandLine.Parse()

	// It is the responsibility of the user of envflag to call flag.Parse to
	// parse command-line flags.
	flag.Parse()

	fmt.Println(*dbEndpoint)
	fmt.Println(*redisEndpoint)
	fmt.Println(*pingURL)
	fmt.Println(*user)

}

Output:
mysql.example:3306
redis.example:6379
http://localhost/ping
nobody

Index

• Variables
• type FlagSet
  • func NewFlagSet(fs *flag.FlagSet) *FlagSet
  • func (fs *FlagSet) Parse()
  • func (fs *FlagSet) String(flagName, envvarName, value, usage string) *string

Examples

• Package
• FlagSet.String

Variables

var CommandLine = NewFlagSet(flag.CommandLine)

CommandLine is the default set of env flags, backed by the default set of command-line flags. The top-level functions of this package are wrappers for the methods of CommandLine.

Types

type FlagSet

type FlagSet struct {
	// contains filtered or unexported fields
}

FlagSet represents a set of defined env flags.

func NewFlagSet

func NewFlagSet(fs *flag.FlagSet) *FlagSet

NewFlagSet returns a new, empty flag set.

func (*FlagSet) Parse

func (fs *FlagSet) Parse()

Parse parses configuration from environment variables and stores non-empty values. It is recommended to call this after all flags are defined and before flag.FlagSet.Parse.

func (*FlagSet) String

func (fs *FlagSet) String(flagName, envvarName, value, usage string) *string

String defines a string flag. A string flag is a single string value, parsed either from an environment variable "<envvarName>" or a command-line argument "-<flagName". The return value is the address of a string variable that stores the value of the flag.

This is a general flag creation utility which is why flagName and envvarName are provided separately rather than generated from a common base.

Example

package main

import (
	"flag"
	"fmt"

	"github.com/LiveRamp/gazette/pkg/envflag"
)

func main() {
	fs := flag.NewFlagSet("Example", flag.PanicOnError)
	efs := envflag.NewFlagSet(fs)

	efs.String("callback", "CALLBACK_URL", "http://my.example/callback", "HTTP callback")
	fmt.Println(fs.Lookup("callback").Name)

}

Output:
callback