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env.go
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env.go
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// Copyright 2015 Sorint.lab
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied
// See the License for the specific language governing permissions and
// limitations under the License.
package flagutil
import (
"fmt"
"os"
"strings"
flag "github.com/spf13/pflag"
)
// SetFlagsFromEnv parses all registered flags in the given flagset,
// and if they are not already set it attempts to set their values from
// environment variables. Environment variables take the name of the flag but
// are UPPERCASE, and any dashes are replaced by underscores. Environment
// variables additionally are prefixed by the given string followed by
// and underscore. For example, if prefix=PREFIX: some-flag => PREFIX_SOME_FLAG
func SetFlagsFromEnv(fs *flag.FlagSet, prefix string) (err error) {
alreadySet := make(map[string]bool)
fs.Visit(func(f *flag.Flag) {
alreadySet[f.Name] = true
})
fs.VisitAll(func(f *flag.Flag) {
if !alreadySet[f.Name] {
key := prefix + "_" + strings.ToUpper(strings.Replace(f.Name, "-", "_", -1))
val := os.Getenv(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
}