/
envFallbackFlag.go
54 lines (47 loc) · 1.37 KB
/
envFallbackFlag.go
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package internal
import (
"fmt"
"os"
)
// EnvFallbackFlag is a custom flag type which retrieves the value from either
// an input flag or env var. If both are set then the flag takes priority.
// This type implements the pflag.Value interface.
type EnvFallbackFlag struct {
flagName string
envVar string
value string
}
// NewEnvFallbackFlag constructs an EnvFallbackFlag with the provided env var
// as a fallback location to read values.
func NewEnvFallbackFlag(flagName, envVar string) *EnvFallbackFlag {
return &EnvFallbackFlag{
flagName: flagName,
envVar: envVar,
}
}
// String returns a default value as a string. This is only used within the
// pflag library. Callers should prefer to use Get().
func (e *EnvFallbackFlag) String() string {
return ""
}
// Set is used within the pflag library to configure value based on a provided
// flag value.
func (e *EnvFallbackFlag) Set(input string) error {
e.value = input
return nil
}
// Get returns the value preferring the flag input over the env var value.
// If neither are set then an error is returned.
func (e *EnvFallbackFlag) Get() (string, error) {
if e.value != "" {
return e.value, nil
}
osValue, ok := os.LookupEnv(e.envVar)
if !ok {
return "", fmt.Errorf("Error: required flag(s) \"%s\" not set", e.flagName)
}
return osValue, nil
}
func (e *EnvFallbackFlag) Type() string {
return "EnvFallbackFlag"
}