libgo/go/os/env.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 // General environment variables.
   6
   7 package os
   8
   9 import "syscall"
  10
  11 // Expand replaces ${var} or $var in the string based on the mapping function.
  12 // For example, os.ExpandEnv(s) is equivalent to os.Expand(s, os.Getenv).
  13 func Expand(s string, mapping func(string) string) string {
  14         buf := make([]byte, 0, 2*len(s))
  15         // ${} is all ASCII, so bytes are fine for this operation.
  16         i := 0
  17         for j := 0; j < len(s); j++ {
  18                 if s[j] == '$' && j+1 < len(s) {
  19                         buf = append(buf, s[i:j]...)
  20                         name, w := getShellName(s[j+1:])
  21                         buf = append(buf, mapping(name)...)
  22                         j += w
  23                         i = j + 1
  24                 }
  25         }
  26         return string(buf) + s[i:]
  27 }
  28
  29 // ExpandEnv replaces ${var} or $var in the string according to the values
  30 // of the current environment variables.  References to undefined
  31 // variables are replaced by the empty string.
  32 func ExpandEnv(s string) string {
  33         return Expand(s, Getenv)
  34 }
  35
  36 // isSpellSpecialVar reports whether the character identifies a special
  37 // shell variable such as $*.
  38 func isShellSpecialVar(c uint8) bool {
  39         switch c {
  40         case '*', '#', '$', '@', '!', '?', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
  41                 return true
  42         }
  43         return false
  44 }
  45
  46 // isAlphaNum reports whether the byte is an ASCII letter, number, or underscore
  47 func isAlphaNum(c uint8) bool {
  48         return c == '_' || '0' <= c && c <= '9' || 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z'
  49 }
  50
  51 // getName returns the name that begins the string and the number of bytes
  52 // consumed to extract it.  If the name is enclosed in {}, it's part of a ${}
  53 // expansion and two more bytes are needed than the length of the name.
  54 func getShellName(s string) (string, int) {
  55         switch {
  56         case s[0] == '{':
  57                 if len(s) > 2 && isShellSpecialVar(s[1]) && s[2] == '}' {
  58                         return s[1:2], 3
  59                 }
  60                 // Scan to closing brace
  61                 for i := 1; i < len(s); i++ {
  62                         if s[i] == '}' {
  63                                 return s[1:i], i + 1
  64                         }
  65                 }
  66                 return "", 1 // Bad syntax; just eat the brace.
  67         case isShellSpecialVar(s[0]):
  68                 return s[0:1], 1
  69         }
  70         // Scan alphanumerics.
  71         var i int
  72         for i = 0; i < len(s) && isAlphaNum(s[i]); i++ {
  73         }
  74         return s[:i], i
  75 }
  76
  77 // Getenv retrieves the value of the environment variable named by the key.
  78 // It returns the value, which will be empty if the variable is not present.
  79 func Getenv(key string) string {
  80         v, _ := syscall.Getenv(key)
  81         return v
  82 }
  83
  84 // Setenv sets the value of the environment variable named by the key.
  85 // It returns an error, if any.
  86 func Setenv(key, value string) error {
  87         err := syscall.Setenv(key, value)
  88         if err != nil {
  89                 return NewSyscallError("setenv", err)
  90         }
  91         return nil
  92 }
  93
  94 // Unsetenv unsets a single environment variable.
  95 func Unsetenv(key string) error {
  96         return syscall.Unsetenv(key)
  97 }
  98
  99 // Clearenv deletes all environment variables.
 100 func Clearenv() {
 101         syscall.Clearenv()
 102 }
 103
 104 // Environ returns a copy of strings representing the environment,
 105 // in the form "key=value".
 106 func Environ() []string {
 107         return syscall.Environ()
 108 }