func (env *Env) Len() int {
	return len(env.Map())
}
Len returns the number of keys in the environment.
Note that len(env) might be different from env.Len(),
because the same key might be set multiple times.
package engine
import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"strconv"
	"strings"
)
type Env []string
func (env *Env) Get(key string) (value string) {
	for _, kv := range *env {
		if strings.Index(kv, "=") == -1 {
			continue
		}
		parts := strings.SplitN(kv, "=", 2)
		if parts[0] != key {
			continue
		}
		if len(parts) < 2 {
			value = ""
		} else {
			value = parts[1]
		}
	}
	return
}
func (env *Env) Exists(key string) bool {
	_, exists := env.Map()[key]
	return exists
}