mirror of
https://github.com/genuinetools/reg.git
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345 lines
8.3 KiB
Go
345 lines
8.3 KiB
Go
package dockerfile
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import (
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"bytes"
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"strings"
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"text/scanner"
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"unicode"
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"github.com/pkg/errors"
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)
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// ShellLex performs shell word splitting and variable expansion.
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//
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// ShellLex takes a string and an array of env variables and
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// process all quotes (" and ') as well as $xxx and ${xxx} env variable
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// tokens. Tries to mimic bash shell process.
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// It doesn't support all flavors of ${xx:...} formats but new ones can
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// be added by adding code to the "special ${} format processing" section
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type ShellLex struct {
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escapeToken rune
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}
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// NewShellLex creates a new ShellLex which uses escapeToken to escape quotes.
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func NewShellLex(escapeToken rune) *ShellLex {
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return &ShellLex{escapeToken: escapeToken}
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}
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// ProcessWord will use the 'env' list of environment variables,
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// and replace any env var references in 'word'.
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func (s *ShellLex) ProcessWord(word string, env []string) (string, error) {
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word, _, err := s.process(word, env)
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return word, err
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}
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// ProcessWords will use the 'env' list of environment variables,
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// and replace any env var references in 'word' then it will also
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// return a slice of strings which represents the 'word'
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// split up based on spaces - taking into account quotes. Note that
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// this splitting is done **after** the env var substitutions are done.
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// Note, each one is trimmed to remove leading and trailing spaces (unless
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// they are quoted", but ProcessWord retains spaces between words.
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func (s *ShellLex) ProcessWords(word string, env []string) ([]string, error) {
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_, words, err := s.process(word, env)
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return words, err
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}
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func (s *ShellLex) process(word string, env []string) (string, []string, error) {
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sw := &shellWord{
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envs: env,
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escapeToken: s.escapeToken,
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}
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sw.scanner.Init(strings.NewReader(word))
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return sw.process(word)
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}
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type shellWord struct {
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scanner scanner.Scanner
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envs []string
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escapeToken rune
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}
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func (sw *shellWord) process(source string) (string, []string, error) {
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word, words, err := sw.processStopOn(scanner.EOF)
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if err != nil {
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err = errors.Wrapf(err, "failed to process %q", source)
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}
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return word, words, err
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}
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type wordsStruct struct {
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word string
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words []string
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inWord bool
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}
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func (w *wordsStruct) addChar(ch rune) {
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if unicode.IsSpace(ch) && w.inWord {
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if len(w.word) != 0 {
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w.words = append(w.words, w.word)
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w.word = ""
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w.inWord = false
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}
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} else if !unicode.IsSpace(ch) {
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w.addRawChar(ch)
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}
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}
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func (w *wordsStruct) addRawChar(ch rune) {
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w.word += string(ch)
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w.inWord = true
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}
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func (w *wordsStruct) addString(str string) {
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var scan scanner.Scanner
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scan.Init(strings.NewReader(str))
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for scan.Peek() != scanner.EOF {
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w.addChar(scan.Next())
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}
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}
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func (w *wordsStruct) addRawString(str string) {
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w.word += str
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w.inWord = true
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}
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func (w *wordsStruct) getWords() []string {
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if len(w.word) > 0 {
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w.words = append(w.words, w.word)
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// Just in case we're called again by mistake
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w.word = ""
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w.inWord = false
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}
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return w.words
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}
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// Process the word, starting at 'pos', and stop when we get to the
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// end of the word or the 'stopChar' character
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func (sw *shellWord) processStopOn(stopChar rune) (string, []string, error) {
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var result bytes.Buffer
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var words wordsStruct
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var charFuncMapping = map[rune]func() (string, error){
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'\'': sw.processSingleQuote,
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'"': sw.processDoubleQuote,
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'$': sw.processDollar,
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}
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for sw.scanner.Peek() != scanner.EOF {
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ch := sw.scanner.Peek()
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if stopChar != scanner.EOF && ch == stopChar {
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sw.scanner.Next()
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break
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}
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if fn, ok := charFuncMapping[ch]; ok {
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// Call special processing func for certain chars
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tmp, err := fn()
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if err != nil {
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return "", []string{}, err
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}
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result.WriteString(tmp)
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if ch == rune('$') {
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words.addString(tmp)
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} else {
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words.addRawString(tmp)
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}
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} else {
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// Not special, just add it to the result
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ch = sw.scanner.Next()
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if ch == sw.escapeToken {
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// '\' (default escape token, but ` allowed) escapes, except end of line
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ch = sw.scanner.Next()
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if ch == scanner.EOF {
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break
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}
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words.addRawChar(ch)
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} else {
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words.addChar(ch)
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}
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result.WriteRune(ch)
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}
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}
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return result.String(), words.getWords(), nil
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}
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func (sw *shellWord) processSingleQuote() (string, error) {
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// All chars between single quotes are taken as-is
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// Note, you can't escape '
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//
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// From the "sh" man page:
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// Single Quotes
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// Enclosing characters in single quotes preserves the literal meaning of
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// all the characters (except single quotes, making it impossible to put
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// single-quotes in a single-quoted string).
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var result bytes.Buffer
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sw.scanner.Next()
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for {
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ch := sw.scanner.Next()
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switch ch {
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case scanner.EOF:
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return "", errors.New("unexpected end of statement while looking for matching single-quote")
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case '\'':
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return result.String(), nil
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}
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result.WriteRune(ch)
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}
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}
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func (sw *shellWord) processDoubleQuote() (string, error) {
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// All chars up to the next " are taken as-is, even ', except any $ chars
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// But you can escape " with a \ (or ` if escape token set accordingly)
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//
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// From the "sh" man page:
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// Double Quotes
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// Enclosing characters within double quotes preserves the literal meaning
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// of all characters except dollarsign ($), backquote (`), and backslash
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// (\). The backslash inside double quotes is historically weird, and
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// serves to quote only the following characters:
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// $ ` " \ <newline>.
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// Otherwise it remains literal.
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var result bytes.Buffer
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sw.scanner.Next()
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for {
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switch sw.scanner.Peek() {
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case scanner.EOF:
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return "", errors.New("unexpected end of statement while looking for matching double-quote")
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case '"':
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sw.scanner.Next()
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return result.String(), nil
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case '$':
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value, err := sw.processDollar()
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if err != nil {
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return "", err
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}
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result.WriteString(value)
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default:
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ch := sw.scanner.Next()
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if ch == sw.escapeToken {
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switch sw.scanner.Peek() {
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case scanner.EOF:
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// Ignore \ at end of word
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continue
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case '"', '$', sw.escapeToken:
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// These chars can be escaped, all other \'s are left as-is
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// Note: for now don't do anything special with ` chars.
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// Not sure what to do with them anyway since we're not going
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// to execute the text in there (not now anyway).
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ch = sw.scanner.Next()
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}
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}
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result.WriteRune(ch)
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}
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}
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}
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func (sw *shellWord) processDollar() (string, error) {
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sw.scanner.Next()
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// $xxx case
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if sw.scanner.Peek() != '{' {
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name := sw.processName()
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if name == "" {
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return "$", nil
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}
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return sw.getEnv(name), nil
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}
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sw.scanner.Next()
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name := sw.processName()
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ch := sw.scanner.Peek()
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if ch == '}' {
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// Normal ${xx} case
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sw.scanner.Next()
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return sw.getEnv(name), nil
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}
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if ch == ':' {
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// Special ${xx:...} format processing
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// Yes it allows for recursive $'s in the ... spot
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sw.scanner.Next() // skip over :
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modifier := sw.scanner.Next()
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word, _, err := sw.processStopOn('}')
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if err != nil {
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return "", err
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}
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// Grab the current value of the variable in question so we
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// can use to to determine what to do based on the modifier
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newValue := sw.getEnv(name)
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switch modifier {
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case '+':
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if newValue != "" {
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newValue = word
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}
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return newValue, nil
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case '-':
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if newValue == "" {
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newValue = word
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}
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return newValue, nil
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default:
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return "", errors.Errorf("unsupported modifier (%c) in substitution", modifier)
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}
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}
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return "", errors.Errorf("missing ':' in substitution")
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}
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func (sw *shellWord) processName() string {
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// Read in a name (alphanumeric or _)
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// If it starts with a numeric then just return $#
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var name bytes.Buffer
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for sw.scanner.Peek() != scanner.EOF {
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ch := sw.scanner.Peek()
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if name.Len() == 0 && unicode.IsDigit(ch) {
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ch = sw.scanner.Next()
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return string(ch)
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}
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if !unicode.IsLetter(ch) && !unicode.IsDigit(ch) && ch != '_' {
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break
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}
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ch = sw.scanner.Next()
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name.WriteRune(ch)
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}
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return name.String()
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}
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func (sw *shellWord) getEnv(name string) string {
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for _, env := range sw.envs {
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i := strings.Index(env, "=")
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if i < 0 {
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if equalEnvKeys(name, env) {
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// Should probably never get here, but just in case treat
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// it like "var" and "var=" are the same
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return ""
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}
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continue
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}
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compareName := env[:i]
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if !equalEnvKeys(name, compareName) {
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continue
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}
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return env[i+1:]
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}
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return ""
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}
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