Initial contribution
diff --git a/src/syscall/env_unix.go b/src/syscall/env_unix.go
new file mode 100644
index 0000000..b5ded9c
--- /dev/null
+++ b/src/syscall/env_unix.go
@@ -0,0 +1,149 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+
+// Unix environment variables.
+
+package syscall
+
+import "sync"
+
+var (
+ // envOnce guards initialization by copyenv, which populates env.
+ envOnce sync.Once
+
+ // envLock guards env and envs.
+ envLock sync.RWMutex
+
+ // env maps from an environment variable to its first occurrence in envs.
+ env map[string]int
+
+ // envs is provided by the runtime. elements are expected to
+ // be of the form "key=value". An empty string means deleted
+ // (or a duplicate to be ignored).
+ envs []string = runtime_envs()
+)
+
+func runtime_envs() []string // in package runtime
+
+// setenv_c and unsetenv_c are provided by the runtime but are no-ops
+// if cgo isn't loaded.
+func setenv_c(k, v string)
+func unsetenv_c(k string)
+
+func copyenv() {
+ env = make(map[string]int)
+ for i, s := range envs {
+ for j := 0; j < len(s); j++ {
+ if s[j] == '=' {
+ key := s[:j]
+ if _, ok := env[key]; !ok {
+ env[key] = i // first mention of key
+ } else {
+ // Clear duplicate keys. This permits Unsetenv to
+ // safely delete only the first item without
+ // worrying about unshadowing a later one,
+ // which might be a security problem.
+ envs[i] = ""
+ }
+ break
+ }
+ }
+ }
+}
+
+func Unsetenv(key string) error {
+ envOnce.Do(copyenv)
+
+ envLock.Lock()
+ defer envLock.Unlock()
+
+ if i, ok := env[key]; ok {
+ envs[i] = ""
+ delete(env, key)
+ }
+ unsetenv_c(key)
+ return nil
+}
+
+func Getenv(key string) (value string, found bool) {
+ envOnce.Do(copyenv)
+ if len(key) == 0 {
+ return "", false
+ }
+
+ envLock.RLock()
+ defer envLock.RUnlock()
+
+ i, ok := env[key]
+ if !ok {
+ return "", false
+ }
+ s := envs[i]
+ for i := 0; i < len(s); i++ {
+ if s[i] == '=' {
+ return s[i+1:], true
+ }
+ }
+ return "", false
+}
+
+func Setenv(key, value string) error {
+ envOnce.Do(copyenv)
+ if len(key) == 0 {
+ return EINVAL
+ }
+ for i := 0; i < len(key); i++ {
+ if key[i] == '=' || key[i] == 0 {
+ return EINVAL
+ }
+ }
+ for i := 0; i < len(value); i++ {
+ if value[i] == 0 {
+ return EINVAL
+ }
+ }
+
+ envLock.Lock()
+ defer envLock.Unlock()
+
+ i, ok := env[key]
+ kv := key + "=" + value
+ if ok {
+ envs[i] = kv
+ } else {
+ i = len(envs)
+ envs = append(envs, kv)
+ }
+ env[key] = i
+ setenv_c(key, value)
+ return nil
+}
+
+func Clearenv() {
+ envOnce.Do(copyenv) // prevent copyenv in Getenv/Setenv
+
+ envLock.Lock()
+ defer envLock.Unlock()
+
+ for k := range env {
+ unsetenv_c(k)
+ }
+ env = make(map[string]int)
+ envs = []string{}
+}
+
+func Environ() []string {
+ envOnce.Do(copyenv)
+ envLock.RLock()
+ defer envLock.RUnlock()
+ a := make([]string, 0, len(envs))
+ for _, env := range envs {
+ if env != "" {
+ a = append(a, env)
+ }
+ }
+ return a
+}
