35 lines
1,015 B
Go
35 lines
1,015 B
Go
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package flag
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import (
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"flag"
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"fmt"
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"os"
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"strings"
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)
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// SetFlagsFromEnv parses all registered flags in the given flagset,
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// and if they are not already set it attempts to set their values from
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// environment variables. Environment variables take the name of the flag but
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// are UPPERCASE, and any dashes are replaced by underscores. Environment
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// variables additionally are prefixed by the given string followed by
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// and underscore. For example, if prefix=PREFIX: some-flag => PREFIX_SOME_FLAG
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func SetFlagsFromEnv(fs *flag.FlagSet, prefix string) error {
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var err error
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alreadySet := make(map[string]bool)
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fs.Visit(func(f *flag.Flag) {
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alreadySet[f.Name] = true
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})
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fs.VisitAll(func(f *flag.Flag) {
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if !alreadySet[f.Name] {
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key := prefix + "_" + strings.ToUpper(strings.Replace(f.Name, "-", "_", -1))
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val := os.Getenv(key)
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if val != "" {
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if serr := fs.Set(f.Name, val); serr != nil {
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err = fmt.Errorf("invalid value %q for %s: %v", val, key, serr)
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}
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}
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}
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})
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return err
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}
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