1 files changed, 53 insertions, 66 deletions

diff --git a/src/pkg/os/env.go b/src/pkg/os/env.go
index bdd2ac293..3a6d79dd0 100644
--- a/src/pkg/os/env.go
+++ b/src/pkg/os/env.go
@@ -1,86 +1,73 @@
-// Copyright 2009 The Go Authors. All rights reserved.
+// 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.
 
-// Environment variables.
+// General environment variables.
 
 package os
 
-import (
-	"once"
-)
-
-// ENOENV is the Error indicating that an environment variable does not exist.
-var ENOENV = NewError("no such environment variable")
-
-var env map[string]string
-
-
-func copyenv() {
-	env = make(map[string]string)
-	for _, s := range Envs {
-		for j := 0; j < len(s); j++ {
-			if s[j] == '=' {
-				env[s[0:j]] = s[j+1:]
-				break
-			}
+// Expand replaces ${var} or $var in the string based on the mapping function.
+// Invocations of undefined variables are replaced with the empty string.
+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, []byte(s[i:j])...)
+			name, w := getShellName(s[j+1:])
+			buf = append(buf, []byte(mapping(name))...)
+			j += w
+			i = j + 1
 		}
 	}
+	return string(buf) + s[i:]
 }
 
-// Getenverror retrieves the value of the environment variable named by the key.
-// It returns the value and an error, if any.
-func Getenverror(key string) (value string, err Error) {
-	once.Do(copyenv)
-
-	if len(key) == 0 {
-		return "", EINVAL
-	}
-	v, ok := env[key]
-	if !ok {
-		return "", ENOENV
-	}
-	return v, nil
-}
-
-// 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, _ := Getenverror(key)
-	return v
+// ShellExpand replaces ${var} or $var in the string according to the values
+// of the operating system's environment variables.  References to undefined
+// variables are replaced by the empty string.
+func ShellExpand(s string) string {
+	return Expand(s, Getenv)
 }
 
-// Setenv sets the value of the environment variable named by the key.
-// It returns an Error, if any.
-func Setenv(key, value string) Error {
-	once.Do(copyenv)
-
-	if len(key) == 0 {
-		return EINVAL
+// 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
 	}
-	env[key] = value
-	return nil
+	return false
 }
 
-// Clearenv deletes all environment variables.
-func Clearenv() {
-	once.Do(copyenv) // prevent copyenv in Getenv/Setenv
-	env = make(map[string]string)
+// 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'
 }
 
-// Environ returns an array of strings representing the environment,
-// in the form "key=value".
-func Environ() []string {
-	once.Do(copyenv)
-	a := make([]string, len(env))
-	i := 0
-	for k, v := range env {
-		// check i < len(a) for safety,
-		// in case env is changing underfoot.
-		if i < len(a) {
-			a[i] = k + "=" + v
-			i++
+// 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 a[0:i]
+	return s[:i], i
 }