env_unix.go

     1  // Copyright 2010 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  //go:build unix || (js && wasm) || plan9 || wasip1
     6  
     7  // Unix environment variables.
     8  
     9  package syscall
    10  
    11  import (
    12  	"runtime"
    13  	"sync"
    14  )
    15  
    16  var (
    17  	// envLock guards env and envs.
    18  	envLock sync.RWMutex
    19  
    20  	// env maps from an environment variable to its first occurrence in envs.
    21  	env map[string]int
    22  
    23  	// envs is provided by the runtime. elements are expected to
    24  	// be of the form "key=value". An empty string means deleted
    25  	// (or a duplicate to be ignored).
    26  	envs []string = runtime_envs()
    27  )
    28  
    29  func runtime_envs() []string // in package runtime
    30  
    31  var copyenv = sync.OnceFunc(func() {
    32  	env = make(map[string]int)
    33  	for i, s := range envs {
    34  		for j := 0; j < len(s); j++ {
    35  			if s[j] == '=' {
    36  				key := s[:j]
    37  				if _, ok := env[key]; !ok {
    38  					env[key] = i // first mention of key
    39  				} else {
    40  					// Clear duplicate keys. This permits Unsetenv to
    41  					// safely delete only the first item without
    42  					// worrying about unshadowing a later one,
    43  					// which might be a security problem.
    44  					envs[i] = ""
    45  				}
    46  				break
    47  			}
    48  		}
    49  	}
    50  })
    51  
    52  func Unsetenv(key string) error {
    53  	copyenv()
    54  
    55  	envLock.Lock()
    56  	defer envLock.Unlock()
    57  
    58  	if i, ok := env[key]; ok {
    59  		envs[i] = ""
    60  		delete(env, key)
    61  	}
    62  	runtimeUnsetenv(key)
    63  	return nil
    64  }
    65  
    66  func Getenv(key string) (value string, found bool) {
    67  	copyenv()
    68  	if len(key) == 0 {
    69  		return "", false
    70  	}
    71  
    72  	envLock.RLock()
    73  	defer envLock.RUnlock()
    74  
    75  	i, ok := env[key]
    76  	if !ok {
    77  		return "", false
    78  	}
    79  	s := envs[i]
    80  	for i := 0; i < len(s); i++ {
    81  		if s[i] == '=' {
    82  			return s[i+1:], true
    83  		}
    84  	}
    85  	return "", false
    86  }
    87  
    88  func Setenv(key, value string) error {
    89  	copyenv()
    90  	if len(key) == 0 {
    91  		return EINVAL
    92  	}
    93  	for i := 0; i < len(key); i++ {
    94  		if key[i] == '=' || key[i] == 0 {
    95  			return EINVAL
    96  		}
    97  	}
    98  	// On Plan 9, null is used as a separator, eg in $path.
    99  	if runtime.GOOS != "plan9" {
   100  		for i := 0; i < len(value); i++ {
   101  			if value[i] == 0 {
   102  				return EINVAL
   103  			}
   104  		}
   105  	}
   106  
   107  	envLock.Lock()
   108  	defer envLock.Unlock()
   109  
   110  	i, ok := env[key]
   111  	kv := key + "=" + value
   112  	if ok {
   113  		envs[i] = kv
   114  	} else {
   115  		i = len(envs)
   116  		envs = append(envs, kv)
   117  	}
   118  	env[key] = i
   119  	runtimeSetenv(key, value)
   120  	return nil
   121  }
   122  
   123  func Clearenv() {
   124  	copyenv()
   125  
   126  	envLock.Lock()
   127  	defer envLock.Unlock()
   128  
   129  	for k := range env {
   130  		runtimeUnsetenv(k)
   131  	}
   132  	env = make(map[string]int)
   133  	envs = []string{}
   134  }
   135  
   136  func Environ() []string {
   137  	copyenv()
   138  	envLock.RLock()
   139  	defer envLock.RUnlock()
   140  	a := make([]string, 0, len(envs))
   141  	for _, env := range envs {
   142  		if env != "" {
   143  			a = append(a, env)
   144  		}
   145  	}
   146  	return a
   147  }
   148
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