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package flagutil
import (
"bufio"
"flag"
"fmt"
"os"
"strings"
)
// SetFlagsFromEnvFile iterates the given flagset and if any flags are not
// already set it attempts to set their values from the given env file. Env
// files may have KEY=VALUE lines where the environment variable names are
// in UPPERCASE, prefixed by the given PREFIX, and dashes are replaced by
// underscores. For example, if prefix=PREFIX, some-flag is named
// PREFIX_SOME_FLAG.
// Comment lines are skipped, but more complex env file parsing is not
// performed.
func SetFlagsFromEnvFile(fs *flag.FlagSet, prefix string, path string) (err error) {
alreadySet := make(map[string]bool)
fs.Visit(func(f *flag.Flag) {
alreadySet[f.Name] = true
})
envs, err := parseEnvFile(path)
if err != nil {
return err
}
fs.VisitAll(func(f *flag.Flag) {
if !alreadySet[f.Name] {
key := prefix + "_" + strings.ToUpper(strings.Replace(f.Name, "-", "_", -1))
val := envs[key]
if val != "" {
if serr := fs.Set(f.Name, val); serr != nil {
err = fmt.Errorf("invalid value %q for %s: %v", val, key, serr)
}
}
}
})
return err
}
func parseEnvFile(path string) (map[string]string, error) {
file, err := os.Open(path)
if err != nil {
return nil, err
}
defer file.Close()
envs := make(map[string]string)
scanner := bufio.NewScanner(file)
for scanner.Scan() {
token := scanner.Text()
if !skipLine(token) {
key, val, err := parseLine(token)
if err == nil {
envs[key] = val
}
}
}
return envs, nil
}
func skipLine(line string) bool {
return len(line) == 0 || strings.HasPrefix(line, "#")
}
func parseLine(line string) (key string, val string, err error) {
trimmed := strings.TrimSpace(line)
pair := strings.SplitN(trimmed, "=", 2)
if len(pair) != 2 {
err = fmt.Errorf("invalid KEY=value line: %q", line)
return
}
key = strings.TrimSpace(pair[0])
val = strings.TrimSpace(pair[1])
return
}
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