104 lines
2.9 KiB
Go
104 lines
2.9 KiB
Go
// Copyright 2010 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// General environment variables.
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package os
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import "syscall"
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// Expand replaces ${var} or $var in the string based on the mapping function.
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// Invocations of undefined variables are replaced with the empty string.
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func Expand(s string, mapping func(string) string) string {
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buf := make([]byte, 0, 2*len(s))
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// ${} is all ASCII, so bytes are fine for this operation.
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i := 0
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for j := 0; j < len(s); j++ {
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if s[j] == '$' && j+1 < len(s) {
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buf = append(buf, s[i:j]...)
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name, w := getShellName(s[j+1:])
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buf = append(buf, mapping(name)...)
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j += w
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i = j + 1
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}
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}
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return string(buf) + s[i:]
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}
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// ExpandEnv replaces ${var} or $var in the string according to the values
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// of the current environment variables. References to undefined
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// variables are replaced by the empty string.
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func ExpandEnv(s string) string {
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return Expand(s, Getenv)
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}
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// isSpellSpecialVar reports whether the character identifies a special
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// shell variable such as $*.
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func isShellSpecialVar(c uint8) bool {
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switch c {
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case '*', '#', '$', '@', '!', '?', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
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return true
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}
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return false
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}
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// isAlphaNum reports whether the byte is an ASCII letter, number, or underscore
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func isAlphaNum(c uint8) bool {
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return c == '_' || '0' <= c && c <= '9' || 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z'
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}
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// getName returns the name that begins the string and the number of bytes
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// consumed to extract it. If the name is enclosed in {}, it's part of a ${}
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// expansion and two more bytes are needed than the length of the name.
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func getShellName(s string) (string, int) {
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switch {
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case s[0] == '{':
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if len(s) > 2 && isShellSpecialVar(s[1]) && s[2] == '}' {
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return s[1:2], 3
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}
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// Scan to closing brace
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for i := 1; i < len(s); i++ {
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if s[i] == '}' {
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return s[1:i], i + 1
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}
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}
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return "", 1 // Bad syntax; just eat the brace.
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case isShellSpecialVar(s[0]):
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return s[0:1], 1
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}
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// Scan alphanumerics.
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var i int
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for i = 0; i < len(s) && isAlphaNum(s[i]); i++ {
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}
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return s[:i], i
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}
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// Getenv retrieves the value of the environment variable named by the key.
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// It returns the value, which will be empty if the variable is not present.
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func Getenv(key string) string {
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v, _ := syscall.Getenv(key)
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return v
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}
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// Setenv sets the value of the environment variable named by the key.
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// It returns an error, if any.
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func Setenv(key, value string) error {
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err := syscall.Setenv(key, value)
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if err != nil {
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return NewSyscallError("setenv", err)
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}
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return nil
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}
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// Clearenv deletes all environment variables.
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func Clearenv() {
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syscall.Clearenv()
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}
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// Environ returns a copy of strings representing the environment,
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// in the form "key=value".
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func Environ() []string {
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return syscall.Environ()
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}
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