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100 lines
2.7 KiB
Go
100 lines
2.7 KiB
Go
// This code comes from golang standard library:
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// https://github.com/golang/go/blob/0e85fd7561de869add933801c531bf25dee9561c/src/os/env.go#L16-L96
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// This file is explicitly excluded from the top repository license.
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// 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 main
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import "fmt"
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// Expand replaces ${var} or $var in the string based on the mapping function.
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func expand(s string, mapping func(string) (string, bool)) string {
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var buf []byte
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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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if buf == nil {
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buf = make([]byte, 0, 2*len(s))
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}
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buf = append(buf, s[i:j]...)
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shellNameInput := s[j+1:]
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name, w := getShellName(shellNameInput)
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if name == "" && w > 0 {
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// Encountered invalid syntax; eat the
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// characters.
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} else if name == "" {
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// Valid syntax, but $ was not followed by a
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// name. Leave the dollar character untouched.
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buf = append(buf, s[j])
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} else {
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replacement, ok := mapping(name)
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if ok {
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buf = append(buf, replacement...)
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} else {
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// preserve enclosing {}
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if shellNameInput[0] == '{' {
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buf = append(buf, fmt.Sprintf("${%s}", name)...)
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} else {
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buf = append(buf, fmt.Sprintf("$%s", name)...)
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}
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}
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}
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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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if buf == nil {
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return s
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}
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return string(buf) + s[i:]
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}
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// isShellSpecialVar 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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// getShellName 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 ${}
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// expansion and two more bytes are needed than the length of the name.
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func getShellName(s string) (string, int) {
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switch {
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case s[0] == '{':
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if len(s) > 2 && isShellSpecialVar(s[1]) && s[2] == '}' {
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return s[1:2], 3
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}
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// Scan to closing brace
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for i := 1; i < len(s); i++ {
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if s[i] == '}' {
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if i == 1 {
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return "", 2 // Bad syntax; eat "${}"
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}
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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; eat "${"
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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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