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// 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.
//go:build unix || (js && wasm) || plan9
// Unix environment variables.
package syscall
import (
"runtime"
"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
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)
}
runtimeUnsetenv(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
}
}
// On Plan 9, null is used as a separator, eg in $path.
if runtime.GOOS != "plan9" {
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
runtimeSetenv(key, value)
return nil
}
func Clearenv() {
envOnce.Do(copyenv) // prevent copyenv in Getenv/Setenv
envLock.Lock()
defer envLock.Unlock()
for k := range env {
runtimeUnsetenv(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
}
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