1 files changed, 108 insertions, 0 deletions
diff --git a/src/os/env.go b/src/os/env.go
new file mode 100644
index 000000000..d0494a476
--- /dev/null
+++ b/src/os/env.go
@@ -0,0 +1,108 @@
+// 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.
+
+// General environment variables.
+
+package os
+
+import "syscall"
+
+// Expand replaces ${var} or $var in the string based on the mapping function.
+// For example, os.ExpandEnv(s) is equivalent to os.Expand(s, os.Getenv).
+func Expand(s string, mapping func(string) string) string {
+	buf := make([]byte, 0, 2*len(s))
+	// ${} is all ASCII, so bytes are fine for this operation.
+	i := 0
+	for j := 0; j < len(s); j++ {
+		if s[j] == '$' && j+1 < len(s) {
+			buf = append(buf, s[i:j]...)
+			name, w := getShellName(s[j+1:])
+			buf = append(buf, mapping(name)...)
+			j += w
+			i = j + 1
+		}
+	}
+	return string(buf) + s[i:]
+}
+
+// ExpandEnv replaces ${var} or $var in the string according to the values
+// of the current environment variables.  References to undefined
+// variables are replaced by the empty string.
+func ExpandEnv(s string) string {
+	return Expand(s, Getenv)
+}
+
+// isSpellSpecialVar reports whether the character identifies a special
+// shell variable such as $*.
+func isShellSpecialVar(c uint8) bool {
+	switch c {
+	case '*', '#', '$', '@', '!', '?', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
+		return true
+	}
+	return false
+}
+
+// isAlphaNum reports whether the byte is an ASCII letter, number, or underscore
+func isAlphaNum(c uint8) bool {
+	return c == '_' || '0' <= c && c <= '9' || 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z'
+}
+
+// getName returns the name that begins the string and the number of bytes
+// consumed to extract it.  If the name is enclosed in {}, it's part of a ${}
+// expansion and two more bytes are needed than the length of the name.
+func getShellName(s string) (string, int) {
+	switch {
+	case s[0] == '{':
+		if len(s) > 2 && isShellSpecialVar(s[1]) && s[2] == '}' {
+			return s[1:2], 3
+		}
+		// Scan to closing brace
+		for i := 1; i < len(s); i++ {
+			if s[i] == '}' {
+				return s[1:i], i + 1
+			}
+		}
+		return "", 1 // Bad syntax; just eat the brace.
+	case isShellSpecialVar(s[0]):
+		return s[0:1], 1
+	}
+	// Scan alphanumerics.
+	var i int
+	for i = 0; i < len(s) && isAlphaNum(s[i]); i++ {
+	}
+	return s[:i], i
+}
+
+// Getenv retrieves the value of the environment variable named by the key.
+// It returns the value, which will be empty if the variable is not present.
+func Getenv(key string) string {
+	v, _ := syscall.Getenv(key)
+	return v
+}
+
+// Setenv sets the value of the environment variable named by the key.
+// It returns an error, if any.
+func Setenv(key, value string) error {
+	err := syscall.Setenv(key, value)
+	if err != nil {
+		return NewSyscallError("setenv", err)
+	}
+	return nil
+}
+
+// Unsetenv unsets a single environment variable.
+func Unsetenv(key string) error {
+	return syscall.Unsetenv(key)
+}
+
+// Clearenv deletes all environment variables.
+func Clearenv() {
+	syscall.Clearenv()
+}
+
+// Environ returns a copy of strings representing the environment,
+// in the form "key=value".
+func Environ() []string {
+	return syscall.Environ()
+}