166 lines
3.5 KiB
Markdown
166 lines
3.5 KiB
Markdown
# envconfig
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[](https://travis-ci.org/kelseyhightower/envconfig)
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```Go
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import "github.com/kelseyhightower/envconfig"
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```
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## Documentation
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See [godoc](http://godoc.org/github.com/kelseyhightower/envconfig)
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## Usage
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Set some environment variables:
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```Bash
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export MYAPP_DEBUG=false
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export MYAPP_PORT=8080
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export MYAPP_USER=Kelsey
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export MYAPP_RATE="0.5"
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export MYAPP_TIMEOUT="3m"
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export MYAPP_USERS="rob,ken,robert"
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```
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Write some code:
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```Go
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package main
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import (
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"fmt"
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"log"
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"time"
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"github.com/kelseyhightower/envconfig"
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)
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type Specification struct {
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Debug bool
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Port int
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User string
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Users []string
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Rate float32
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Timeout time.Duration
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}
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func main() {
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var s Specification
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err := envconfig.Process("myapp", &s)
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if err != nil {
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log.Fatal(err.Error())
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}
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format := "Debug: %v\nPort: %d\nUser: %s\nRate: %f\nTimeout: %s\n"
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_, err = fmt.Printf(format, s.Debug, s.Port, s.User, s.Rate)
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if err != nil {
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log.Fatal(err.Error())
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}
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fmt.Println("Users:")
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for _, u := range s.Users {
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fmt.Printf(" %s\n", u)
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}
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}
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```
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Results:
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```Bash
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Debug: false
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Port: 8080
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User: Kelsey
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Rate: 0.500000
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Timeout: 3m0s
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Users:
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rob
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ken
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robert
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```
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## Struct Tag Support
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Envconfig supports the use of struct tags to specify alternate, default, and required
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environment variables.
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For example, consider the following struct:
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```Go
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type Specification struct {
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MultiWordVar string `envconfig:"multi_word_var"`
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DefaultVar string `default:"foobar"`
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RequiredVar string `required:"true"`
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IgnoredVar string `ignored:"true"`
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}
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```
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Envconfig will process value for `MultiWordVar` by populating it with the
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value for `MYAPP_MULTI_WORD_VAR`.
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```Bash
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export MYAPP_MULTI_WORD_VAR="this will be the value"
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# export MYAPP_MULTIWORDVAR="and this will not"
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```
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If envconfig can't find an environment variable value for `MYAPP_DEFAULTVAR`,
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it will populate it with "foobar" as a default value.
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If envconfig can't find an environment variable value for `MYAPP_REQUIREDVAR`,
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it will return an error when asked to process the struct.
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If envconfig can't find an environment variable in the form `PREFIX_MYVAR`, and there
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is a struct tag defined, it will try to populate your variable with an environment
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variable that directly matches the envconfig tag in your struct definition:
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```shell
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export SERVICE_HOST=127.0.0.1
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export MYAPP_DEBUG=true
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```
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```Go
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type Specification struct {
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ServiceHost string `envconfig:"SERVICE_HOST"`
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Debug bool
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}
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```
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Envconfig won't process a field with the "ignored" tag set to "true", even if a corresponding
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environment variable is set.
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## Supported Struct Field Types
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envconfig supports supports these struct field types:
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* string
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* int8, int16, int32, int64
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* bool
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* float32, float64
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* [encoding.TextUnmarshaler](https://golang.org/pkg/encoding/#TextUnmarshaler)
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Embedded structs using these fields are also supported.
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## Custom Decoders
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Any field whose type (or pointer-to-type) implements `envconfig.Decoder` can
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control its own deserialization:
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```Bash
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export DNS_SERVER=8.8.8.8
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```
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```Go
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type IPDecoder net.IP
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func (ipd *IPDecoder) Decode(value string) error {
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*ipd = IPDecoder(net.ParseIP(value))
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return nil
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}
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type DNSConfig struct {
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Address IPDecoder `envconfig:"DNS_SERVER"`
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}
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```
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Also, envconfig will use a `Set(string) error` method like from the
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[flag.Value](https://godoc.org/flag#Value) interface if implemented.
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