Put the gotenv package on your `import` statement:
```go
import "github.com/subosito/gotenv"
```
To modify your app environment variables, `gotenv` expose 2 main functions:
-`gotenv.Load`
-`gotenv.Apply`
By default, `gotenv.Load` will look for a file called `.env` in the current working directory.
Behind the scene, it will then load `.env` file and export the valid variables to the environment variables. Make sure you call the method as soon as possible to ensure it loads all variables, say, put it on `init()` function.
Once loaded you can use `os.Getenv()` to get the value of the variable.
Let's say you have `.env` file:
```
APP_ID=1234567
APP_SECRET=abcdef
```
Here's the example of your app:
```go
package main
import (
"github.com/subosito/gotenv"
"log"
"os"
)
func init() {
gotenv.Load()
}
func main() {
log.Println(os.Getenv("APP_ID")) // "1234567"
log.Println(os.Getenv("APP_SECRET")) // "abcdef"
}
```
You can also load other than `.env` file if you wish. Just supply filenames when calling `Load()`. It will load them in order and the first value set for a variable will win.:
```go
gotenv.Load(".env.production", "credentials")
```
While `gotenv.Load` loads entries from `.env` file, `gotenv.Apply` allows you to use any `io.Reader`:
```go
gotenv.Apply(strings.NewReader("APP_ID=1234567"))
log.Println(os.Getenv("APP_ID"))
// Output: "1234567"
```
Both `gotenv.Load` and `gotenv.Apply`**DO NOT** overrides existing environment variables. If you want to override existing ones, you can see section below.
### Environment Overrides
Besides above functions, `gotenv` also provides another functions that overrides existing:
-`gotenv.OverLoad`
-`gotenv.OverApply`
Here's the example of this overrides behavior:
```go
os.Setenv("HELLO", "world")
// NOTE: using Apply existing value will be reserved
gotenv.Apply(strings.NewReader("HELLO=universe"))
fmt.Println(os.Getenv("HELLO"))
// Output: "world"
// NOTE: using OverApply existing value will be overridden
Both `gotenv.Load` and `gotenv.OverLoad` returns an error on something wrong occurred, like your env file is not exist, and so on. To make it easier to use, `gotenv` also provides `gotenv.Must` helper, to let it panic when an error returned.
```go
err := gotenv.Load(".env-is-not-exist")
fmt.Println("error", err)
// error: open .env-is-not-exist: no such file or directory
gotenv.Must(gotenv.Load, ".env-is-not-exist")
// it will throw a panic
// panic: open .env-is-not-exist: no such file or directory
```
### Another Scenario
Just in case you want to parse environment variables from any `io.Reader`, gotenv keeps its `Parse` and `StrictParse` function as public API so you can use that.
`Parse` ignores invalid lines and returns `Env` of valid environment variables, while `StrictParse` returns an error for invalid lines.
## Notes
The gotenv package is a Go port of [`dotenv`](https://github.com/bkeepers/dotenv) project with some additions made for Go. For general features, it aims to be compatible as close as possible.
