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expand.go
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expand.go
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// Copyright 2024 The CUE Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package cmd
// The code below is copied and modified from the Go source as of
// 9cc0f9cba2f2db97f5ba6c2c482bafaaa34c0381
//
// 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.
// expand replaces ${var} or $var in the string based on the mapping function
// if the mapping function returns true.
func expand(s string, mapping func(string) (bool, string)) string {
var buf []byte
// ${} is all ASCII, so bytes are fine for this operation.
i := 0
for j := 0; j < len(s); j++ {
if s[j] == '$' && j+1 < len(s) {
if buf == nil {
buf = make([]byte, 0, 2*len(s))
}
buf = append(buf, s[i:j]...)
name, w := getShellName(s[j+1:])
if name == "" && w > 0 {
// Encountered invalid syntax; eat the
// characters.
} else if name == "" {
// Valid syntax, but $ was not followed by a
// name. Leave the dollar character untouched.
buf = append(buf, s[j])
} else {
mapped, repl := mapping(name)
if mapped {
buf = append(buf, repl...)
} else {
buf = append(buf, s[j:j+1+w]...)
}
}
j += w
i = j + 1
}
}
if buf == nil {
return s
}
return string(buf) + s[i:]
}
// isShellSpecialVar 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'
}
// getShellName 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 ${}
// expansion and two more bytes are needed than the length of the name.
func getShellName(s string) (string, int) {
switch {
case s[0] == '{':
if len(s) > 2 && isShellSpecialVar(s[1]) && s[2] == '}' {
return s[1:2], 3
}
// Scan to closing brace
for i := 1; i < len(s); i++ {
if s[i] == '}' {
if i == 1 {
return "", 2 // Bad syntax; eat "${}"
}
return s[1:i], i + 1
}
}
return "", 1 // Bad syntax; eat "${"
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
}