expand.go

package main

// Modified copy of os/env.go. The Go LICENSE file is included below:

// Copyright (c) 2009 The Go Authors. All rights reserved.

// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:

//    * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//    * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//    * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.

// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// 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.

func expand(s string, escape rune, mapping func(string) string) string {
	buf := make([]byte, 0, 2*len(s))
	i := 0
	escaped := string([]rune{escape}) + "$"
	for j := 0; j < len(s); j++ {
		if j+len(escaped) < len(s) && s[j:j+len(escaped)] == escaped {
			buf = append(buf, s[i:j+1]...)
			j += 2
			i = j
			continue
		}
		if s[j] == '$' && j+1 < len(s) {
			buf = append(buf, s[i:j]...)
			name, w := variableName(s[j+1:])
			buf = append(buf, mapping(name)...)
			j += w
			i = j + 1
		}
	}
	return string(buf) + s[i:]
}

func isAlphaNum(c uint8) bool {
	return c == '_' || '0' <= c && c <= '9' || 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z'
}

func variableName(s string) (string, int) {
	if s[0] == '{' {
		for i := 1; i < len(s); i++ {
			if s[i] == '}' {
				return s[1:i], i + 1
			}
		}
		return "", 1
	}
	var i int
	for i = 0; i < len(s) && isAlphaNum(s[i]); i++ {
	}
	return s[:i], i
}