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
7package os
8
9import "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).
13func 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.
32func ExpandEnv(s string) string {
33	return Expand(s, Getenv)
34}
35
36// isShellSpecialVar reports whether the character identifies a special
37// shell variable such as $*.
38func isShellSpecialVar(c uint8) bool {
39	switch c {
40	case '*', '#', '$', '@', '!', '?', '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
47func isAlphaNum(c uint8) bool {
48	return c == '_' || '0' <= c && c <= '9' || 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z'
49}
50
51// getShellName 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.
54func 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.
79func Getenv(key string) string {
80	v, _ := syscall.Getenv(key)
81	return v
82}
83
84// LookupEnv retrieves the value of the environment variable named
85// by the key. If the variable is present in the environment the
86// value (which may be empty) is returned and the boolean is true.
87// Otherwise the returned value will be empty and the boolean will
88// be false.
89func LookupEnv(key string) (string, bool) {
90	return syscall.Getenv(key)
91}
92
93// Setenv sets the value of the environment variable named by the key.
94// It returns an error, if any.
95func Setenv(key, value string) error {
96	err := syscall.Setenv(key, value)
97	if err != nil {
98		return NewSyscallError("setenv", err)
99	}
100	return nil
101}
102
103// Unsetenv unsets a single environment variable.
104func Unsetenv(key string) error {
105	return syscall.Unsetenv(key)
106}
107
108// Clearenv deletes all environment variables.
109func Clearenv() {
110	syscall.Clearenv()
111}
112
113// Environ returns a copy of strings representing the environment,
114// in the form "key=value".
115func Environ() []string {
116	return syscall.Environ()
117}
118