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 (
10 "internal/testlog"
11 "syscall"
12 )
13 14 // Expand replaces ${var} or $var in the string based on the mapping function.
15 // For example, os.ExpandEnv(s) is equivalent to os.Expand(s, os.Getenv).
16 func Expand(s string, mapping func(string) string) string {
17 var buf []byte
18 // ${} is all ASCII, so bytes are fine for this operation.
19 i := 0
20 for j := 0; j < len(s); j++ {
21 if s[j] == '$' && j+1 < len(s) {
22 if buf == nil {
23 buf = make([]byte, 0, 2*len(s))
24 }
25 buf = append(buf, s[i:j]...)
26 name, w := getShellName(s[j+1:])
27 if name == "" && w > 0 {
28 // Encountered invalid syntax; eat the
29 // characters.
30 } else if name == "" {
31 // Valid syntax, but $ was not followed by a
32 // name. Leave the dollar character untouched.
33 buf = append(buf, s[j])
34 } else {
35 buf = append(buf, mapping(name)...)
36 }
37 j += w
38 i = j + 1
39 }
40 }
41 if buf == nil {
42 return s
43 }
44 return string(buf) + s[i:]
45 }
46 47 // ExpandEnv replaces ${var} or $var in the string according to the values
48 // of the current environment variables. References to undefined
49 // variables are replaced by the empty string.
50 func ExpandEnv(s string) string {
51 return Expand(s, Getenv)
52 }
53 54 // isShellSpecialVar reports whether the character identifies a special
55 // shell variable such as $*.
56 func isShellSpecialVar(c uint8) bool {
57 switch c {
58 case '*', '#', '$', '@', '!', '?', '-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
59 return true
60 }
61 return false
62 }
63 64 // isAlphaNum reports whether the byte is an ASCII letter, number, or underscore
65 func isAlphaNum(c uint8) bool {
66 return c == '_' || '0' <= c && c <= '9' || 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z'
67 }
68 69 // getShellName returns the name that begins the string and the number of bytes
70 // consumed to extract it. If the name is enclosed in {}, it's part of a ${}
71 // expansion and two more bytes are needed than the length of the name.
72 func getShellName(s string) (string, int) {
73 switch {
74 case s[0] == '{':
75 if len(s) > 2 && isShellSpecialVar(s[1]) && s[2] == '}' {
76 return s[1:2], 3
77 }
78 // Scan to closing brace
79 for i := 1; i < len(s); i++ {
80 if s[i] == '}' {
81 if i == 1 {
82 return "", 2 // Bad syntax; eat "${}"
83 }
84 return s[1:i], i + 1
85 }
86 }
87 return "", 1 // Bad syntax; eat "${"
88 case isShellSpecialVar(s[0]):
89 return s[0:1], 1
90 }
91 // Scan alphanumerics.
92 var i int
93 for i = 0; i < len(s) && isAlphaNum(s[i]); i++ {
94 }
95 return s[:i], i
96 }
97 98 // Getenv retrieves the value of the environment variable named by the key.
99 // It returns the value, which will be empty if the variable is not present.
100 // To distinguish between an empty value and an unset value, use LookupEnv.
101 func Getenv(key string) string {
102 testlog.Getenv(key)
103 v, _ := syscall.Getenv(key)
104 return v
105 }
106 107 // LookupEnv retrieves the value of the environment variable named
108 // by the key. If the variable is present in the environment the
109 // value (which may be empty) is returned and the boolean is true.
110 // Otherwise the returned value will be empty and the boolean will
111 // be false.
112 func LookupEnv(key string) (string, bool) {
113 testlog.Getenv(key)
114 return syscall.Getenv(key)
115 }
116 117 // Setenv sets the value of the environment variable named by the key.
118 // It returns an error, if any.
119 func Setenv(key, value string) error {
120 err := syscall.Setenv(key, value)
121 if err != nil {
122 return NewSyscallError("setenv", err)
123 }
124 return nil
125 }
126 127 // Unsetenv unsets a single environment variable.
128 func Unsetenv(key string) error {
129 return syscall.Unsetenv(key)
130 }
131 132 // Clearenv deletes all environment variables.
133 func Clearenv() {
134 syscall.Clearenv()
135 }
136 137 // Environ returns a copy of strings representing the environment,
138 // in the form "key=value".
139 func Environ() []string {
140 return syscall.Environ()
141 }
142