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// Package flagenv provides the ability to populate flags from
// environment variables.
package flagenv
import (
"flag"
"fmt"
"log"
"os"
"strings"
)
// Specify a prefix for environment variables.
var Prefix = ""
func contains(list []*flag.Flag, f *flag.Flag) bool {
for _, i := range list {
if i == f {
return true
}
}
return false
}
// ParseSet parses the given flagset. The specified prefix will be applied to
// the environment variable names.
func ParseSet(prefix string, set *flag.FlagSet) error {
var explicit []*flag.Flag
var all []*flag.Flag
set.Visit(func(f *flag.Flag) {
explicit = append(explicit, f)
})
var err error
set.VisitAll(func(f *flag.Flag) {
if err != nil {
return
}
all = append(all, f)
if !contains(explicit, f) {
name := strings.Replace(f.Name, ".", "_", -1)
name = strings.Replace(name, "-", "_", -1)
if prefix != "" {
name = prefix + name
}
name = strings.ToUpper(name)
val := os.Getenv(name)
if val != "" {
if ferr := f.Value.Set(val); ferr != nil {
err = fmt.Errorf("failed to set flag %q with value %q", f.Name, val)
}
}
}
})
return err
}
// Parse will set each defined flag from its corresponding environment
// variable . If dots or dash are presents in the flag name, they will be
// converted to underscores.
//
// If Parse fails, a fatal error is issued.
func Parse() {
if err := ParseSet(Prefix, flag.CommandLine); err != nil {
log.Fatalln(err)
}
}
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