refactor(shellquote): replace go-shellquote with custom shell quoting implementation

utils/shellquote/shellquote.go

@@ -0,0 +1,115 @@
+package shellquote
+
+import (
+	"errors"
+	"strings"
+)
+
+var (
+	ErrUnterminatedSingleQuote = errors.New("unterminated single-quoted string")
+	ErrUnterminatedDoubleQuote = errors.New("unterminated double-quoted string")
+	ErrUnterminatedEscape      = errors.New("unterminated backslash-escape")
+)
+
+type state int
+
+const (
+	stateUnquoted state = iota
+	stateSingleQuoted
+	stateDoubleQuoted
+)
+
+// Split splits a string into words following POSIX-like shell quoting rules.
+// It handles single quotes, double quotes, and backslash escapes.
+func Split(input string) ([]string, error) {
+	var words []string
+	var word strings.Builder
+	inWord := false
+	parseState := stateUnquoted
+
+	i := 0
+	for i < len(input) {
+		ch := input[i]
+
+		switch parseState {
+		case stateUnquoted:
+			switch {
+			case ch == '\\':
+				if i+1 >= len(input) {
+					return nil, ErrUnterminatedEscape
+				}
+				if input[i+1] == '\n' {
+					// Line continuation: skip both backslash and newline
+					i += 2
+					continue
+				}
+				i++
+				word.WriteByte(input[i])
+				inWord = true
+			case ch == '\'':
+				parseState = stateSingleQuoted
+				inWord = true
+			case ch == '"':
+				parseState = stateDoubleQuoted
+				inWord = true
+			case ch == ' ' || ch == '\t' || ch == '\n':
+				if inWord {
+					words = append(words, word.String())
+					word.Reset()
+					inWord = false
+				}
+			default:
+				word.WriteByte(ch)
+				inWord = true
+			}
+
+		case stateSingleQuoted:
+			if ch == '\'' {
+				parseState = stateUnquoted
+			} else {
+				word.WriteByte(ch)
+			}
+
+		case stateDoubleQuoted:
+			switch {
+			case ch == '"':
+				parseState = stateUnquoted
+			case ch == '\\':
+				if i+1 >= len(input) {
+					return nil, ErrUnterminatedEscape
+				}
+				next := input[i+1]
+				// In double quotes, backslash only escapes: $ ` " \n \
+				if next == '$' || next == '`' || next == '"' || next == '\n' || next == '\\' {
+					if next == '\n' {
+						// Line continuation: skip both backslash and newline
+						i += 2
+						continue
+					}
+					i++
+					word.WriteByte(next)
+				} else {
+					// Backslash is literal for other characters
+					word.WriteByte(ch)
+				}
+			default:
+				word.WriteByte(ch)
+			}
+		}
+
+		i++
+	}
+
+	switch parseState {
+	case stateSingleQuoted:
+		return nil, ErrUnterminatedSingleQuote
+	case stateDoubleQuoted:
+		return nil, ErrUnterminatedDoubleQuote
+	}
+
+	if inWord {
+		words = append(words, word.String())
+	}
+
+	return words, nil
+}