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|
package envflag
import (
"flag"
"fmt"
"os"
"regexp"
"strings"
)
// Option type for configing the parsing.
type Option option
type option func(*config)
// FlagConverterFunc functions are used to update flag name for envvar lookups.
type FlagConverterFunc func(flag string) string
// UsageUpdaterFunc functions are used to update flag usage strings.
type UsageUpdaterFunc func(key, usage string) string
type config struct {
flagConverter FlagConverterFunc
usageUpdater UsageUpdaterFunc
}
// UsageUpdater enables configurable flag usage updates.
func UsageUpdater(f UsageUpdaterFunc) Option {
return func(cfg *config) {
cfg.usageUpdater = f
}
}
// UsagePrefixer prefixes the flag usage with [envvar].
func UsagePrefixer() Option {
return func(cfg *config) {
cfg.usageUpdater = usagePrefixer
}
}
// UsageSuffixer suffixes the flag usage with [envvar].
func UsageSuffixer() Option {
return func(cfg *config) {
cfg.usageUpdater = usageSuffixer
}
}
// FlagConverter converts the flag name to an environment variable key.
func FlagConverter(f FlagConverterFunc) Option {
return func(cfg *config) {
cfg.flagConverter = f
}
}
// ParseWithEnv parses the command-line flags from os.Args[1:]. Must be called
// after all flags are defined and before flags are accessed by the program.
func Parse(opts ...Option) error {
return parseFlagSetWithEnv(flag.CommandLine, os.Args[1:], opts...)
}
// ParseFlagSetWithEnv parses flag definitions from the argument list, which
// should not include the command name. Must be called after all flags in the
// FlagSet are defined and before flags are accessed by the program. The return
// value will be ErrHelp if -help or -h were set but not defined.
func ParseFlagSet(fs *flag.FlagSet, arguments []string, opts ...Option) error {
return parseFlagSetWithEnv(fs, arguments, opts...)
}
func parseFlagSetWithEnv(fs *flag.FlagSet, arguments []string, opts ...Option) error {
if fs.Parsed() {
return fmt.Errorf("flag has already been parsed")
}
cfg := &config{
flagConverter: flagToEnv(),
}
for _, o := range opts {
o(cfg)
}
var nerr error
fs.VisitAll(func(f *flag.Flag) {
envKey := cfg.flagConverter(f.Name)
if cfg.usageUpdater != nil {
f.Usage = cfg.usageUpdater(envKey, f.Usage)
}
if envVal := os.Getenv(envKey); envVal != "" {
err := f.Value.Set(envVal)
if err != nil && nerr == nil {
nerr = err
}
}
})
if nerr != nil {
return nerr
}
return fs.Parse(arguments)
}
// convert this-format to THIS_FORMAT
func flagToEnv() func(string) string {
re := regexp.MustCompile("[^a-zA-Z0-9_]+")
return func(f string) string {
return strings.ToUpper(re.ReplaceAllLiteralString(f, "_"))
}
}
func usageSuffixer(key, usage string) string {
envSuffix := fmt.Sprintf("[%s]", key)
if strings.HasSuffix(usage, envSuffix) {
return usage
}
return fmt.Sprintf("%s %s", usage, envSuffix)
}
func usagePrefixer(key, usage string) string {
envPrefix := fmt.Sprintf("[%s]", key)
if strings.HasPrefix(usage, envPrefix) {
return usage
}
return fmt.Sprintf("%s %s", envPrefix, usage)
}
|
