next

        pub fn next(self: *Self) ?[:0]const u8 {
            if (!self.skipWhitespace()) {
                return null;
            }

            var backslash_count: usize = 0;
            var in_quote = false;
            while (true) : (self.index += 1) {
                const character = if (self.index != self.cmd_line.len) self.cmd_line[self.index] else 0;
                switch (character) {
                    0 => {
                        self.emitBackslashes(backslash_count);
                        self.buffer[self.end] = 0;
                        const token = self.buffer[self.start..self.end :0];
                        self.end += 1;
                        self.start = self.end;
                        return token;
                    },
                    '"', '\'' => {
                        if (!options.single_quotes and character == '\'') {
                            self.emitBackslashes(backslash_count);
                            backslash_count = 0;
                            self.emitCharacter(character);
                            continue;
                        }
                        const quote_is_real = backslash_count % 2 == 0;
                        self.emitBackslashes(backslash_count / 2);
                        backslash_count = 0;

                        if (quote_is_real) {
                            in_quote = !in_quote;
                        } else {
                            self.emitCharacter('"');
                        }
                    },
                    '\\' => {
                        backslash_count += 1;
                    },
                    ' ', '\t', '\r', '\n' => {
                        self.emitBackslashes(backslash_count);
                        backslash_count = 0;
                        if (in_quote) {
                            self.emitCharacter(character);
                        } else {
                            self.buffer[self.end] = 0;
                            const token = self.buffer[self.start..self.end :0];
                            self.end += 1;
                            self.start = self.end;
                            return token;
                        }
                    },
                    else => {
                        self.emitBackslashes(backslash_count);
                        backslash_count = 0;
                        self.emitCharacter(character);
                    },
                }
            }
        }