README
¶
envflag 
Minimalist approach to wiring up the standard flag package to the environment.
Usage
func main() {
listenAddr := flag.String("addr", ":8080", "server listen address")
flag.Parse()
envflag.SetPrefix("myapp")
envflag.Parse()
fmt.Printf("listenAddr is %q\n", *listenAddr)
}
Rationale
This package connects the standard flag package to the environment with a minimum of ceremony.
12-factor apps store their configuration in the environment. It's also useful, however, to accept command-line flags: they make a program easier to use, and serve as documentation.
Example
package main
import (
"flag"
"fmt"
"os"
"github.com/dcowgill/envflag"
)
func main() {
fs := flag.NewFlagSet(os.Args[0], flag.ExitOnError)
listenAddr := fs.String("addr", ":8888", "server listen address")
timeout := fs.Int("timeout", 10, "client timeout in seconds")
fs.Parse(nil) // simulate no command-line args
// Normally this would happen outside the program.
os.Setenv("MYAPP_LISTEN_ADDR", ":9999")
os.Setenv("MYAPP_TIMEOUT", "42")
vs := envflag.NewVarSet(fs)
vs.SetPrefix("myapp")
vs.RenameFlag("addr", "listen-addr")
vs.Parse()
fmt.Println(*listenAddr) // prints ":9999"
fmt.Println(*timeout) // prints "42"
}
Documentation
¶
Overview ¶
Package envflag parses command-line flags defined by package flag from the environment.
Usage:
package main
import (
"flag"
"fmt"
"github.com/dcowgill/envflag"
)
func main() {
listenAddr := flag.String("listen-addr", ":8080", "server listen address")
flag.Parse()
envflag.SetPrefix("myapp")
envflag.Parse()
fmt.Printf("listenAddr is %q\n", *listenAddr)
}
An environment variable will not override a flag, but will override its default value:
$ go run example.go listenAddr is ":8080" $ MYAPP_LISTEN_ADDR=:7070 go run example.go listenAddr is ":7070" $ MYAPP_LISTEN_ADDR=:7070 go run example.go -listen-addr=:9090 listenAddr is ":9090"
Flag names are automatically converted to environment variable keys according to the following rules:
- Non-ASCII runes are omitted.
- Uppercase letters, digits, and underscores are preserved.
- Lowercase letters are changed to uppercase.
- Hyphens are changed to underscores.
- All other runes are omitted.
- Prepend an underscore if a variable name would otherwise begin with a digit.
Index ¶
Constants ¶
This section is empty.
Variables ¶
var CommandLine = NewVarSet(flag.CommandLine)
CommandLine wraps flag.CommandLine, the default set of command-line flags. The top-level functions, such as SetPrefix and Parse, are wrappers for the methods of CommandLine.
Functions ¶
func Parse ¶
func Parse()
Parse sets the value of flags that were not provided on the command-line but are set in the environment.
func RenameFlag ¶
func RenameFlag(old, new string)
RenameFlag modifies a flag name before it is converted to an environment key. The new name will be transformed by the same process as any other flag name.
Types ¶
type VarSet ¶
type VarSet struct {
// LookupEnv is an optional replacement for os.LookupEnv in this VarSet.
LookupEnv func(key string) (string, bool)
// contains filtered or unexported fields
}
A VarSet wraps a flag.FlagSet. The zero value of a VarSet should not be used.
A program that uses the top-level functions in package flag should also use the top-level functions in this package. Otherwise, it must wrap each flag.FlagSet with a VarSet to connect it to the environment.
func NewVarSet ¶
NewVarSet creates a new VarSet with the specified flag set and error handling property.
func (*VarSet) Parse ¶
Parse sets the value of flags that were not provided on the command-line but are set in the environment.
func (*VarSet) RenameFlag ¶
RenameFlag modifies a flag name before it is converted to an environment key. The new name will be transformed by the same process as any other flag name.
Source Files