diff --git a/ruby/shell/string_parser.rb b/ruby/shell/string_parser.rb
index 0379b1a..d64ce72 100644
--- a/ruby/shell/string_parser.rb
+++ b/ruby/shell/string_parser.rb
@@ -1,76 +1,368 @@
-require "shell/quote_cursor"
-
 module Shell
   class StringParser
-    class << self
-      def split_commands(line)
-        commands = []
-        command = +""
-        cursor = QuoteCursor.new
-        next_op = :always
-        i = 0
+    Token = Struct.new(:type, :value, keyword_init: true)
 
-        while i < line.length
-          c = line[i]
-          if cursor.unquoted?
-            case c
-            when ";"
-              commands << {command: command, op: next_op}
-              command = +""
-              next_op = :always
-              i += 1
-              next
-            when "&"
-              if line[i + 1] == "&"
-                if command.strip.empty?
-                  raise ArgumentError, "syntax error near unexpected token `&&`"
-                end
-                commands << {command: command, op: next_op}
-                command = +""
-                next_op = :and
-                i += 2
-                next
-              end
-            end
-          end
-
-          segment, i = cursor.consume(line, i)
-          command << segment
-        end
-
-        if next_op == :and && command.strip.empty?
-          raise ArgumentError, "syntax error: expected command after `&&`"
-        end
-
-        commands << {command: command, op: next_op}
-        commands
+    class Scanner
+      def initialize(line, index: 0)
+        @line = line
+        @index = index
       end
 
-      def read_dollar_paren(line, start_index)
-        output = +""
-        i = start_index
-        depth = 1
-        cursor = QuoteCursor.new
+      attr_reader :index
 
-        while i < line.length
-          c = line[i]
+      def tokenize_command_list
+        tokens = []
+        segment_start = index
 
-          if cursor.unquoted?
-            case c
-            when "("
-              depth += 1
-            when ")"
-              depth -= 1
-              return [output, i + 1] if depth.zero?
-            end
+        until eof?
+          c = current_char
+          if c == ";"
+            tokens << Token.new(type: :text, value: @line[segment_start...index])
+            tokens << Token.new(type: :separator, value: :always)
+            advance
+            segment_start = index
+            next
           end
 
-          segment, i = cursor.consume(line, i)
-          output << segment
+          if c == "&" && peek(1) == "&"
+            tokens << Token.new(type: :text, value: @line[segment_start...index])
+            tokens << Token.new(type: :separator, value: :and)
+            advance(2)
+            segment_start = index
+            next
+          end
+
+          case c
+          when "\\"
+            advance_escape
+          when "'"
+            skip_single_quoted
+          when "\""
+            skip_double_quoted
+          when "`"
+            skip_backtick
+          when "$"
+            if peek(1) == "("
+              if peek(2) == "("
+                skip_arithmetic_substitution
+              else
+                skip_command_substitution
+              end
+            else
+              advance
+            end
+          else
+            advance
+          end
+        end
+
+        tokens << Token.new(type: :text, value: @line[segment_start...index])
+        tokens
+      end
+
+      # Reads the contents and end-index for a command substitution body, where
+      # index points to the first character after "$(".
+      def read_dollar_paren_body
+        output = +""
+        depth = 1
+
+        until eof?
+          c = current_char
+
+          if c == "\\"
+            output << read_escape
+            next
+          end
+
+          if c == "'"
+            output << read_single_quoted
+            next
+          end
+
+          if c == "\""
+            output << read_double_quoted
+            next
+          end
+
+          if c == "`"
+            output << read_backtick
+            next
+          end
+
+          if c == "$" && peek(1) == "("
+            if peek(2) == "("
+              output << read_arithmetic_substitution
+            else
+              output << "$("
+              advance(2)
+              depth += 1
+            end
+            next
+          end
+
+          if c == "("
+            output << c
+            depth += 1
+            advance
+            next
+          end
+
+          if c == ")"
+            depth -= 1
+            if depth.zero?
+              return [output, index + 1]
+            end
+            output << c
+            advance
+            next
+          end
+
+          output << c
+          advance
         end
 
         raise ArgumentError, "Unmatched $(...)"
       end
+
+      private
+
+      def eof?
+        index >= @line.length
+      end
+
+      def current_char
+        @line[index]
+      end
+
+      def peek(offset)
+        @line[index + offset]
+      end
+
+      def advance(count = 1)
+        @index += count
+      end
+
+      def advance_escape
+        advance
+        advance unless eof?
+      end
+
+      def skip_single_quoted
+        advance # opening quote
+        until eof?
+          if current_char == "'"
+            advance
+            return
+          end
+          advance
+        end
+        raise ArgumentError, "Unmatched quote"
+      end
+
+      def skip_double_quoted
+        advance # opening quote
+        until eof?
+          c = current_char
+          case c
+          when "\\"
+            advance_escape
+          when "\""
+            advance
+            return
+          when "`"
+            skip_backtick
+          when "$"
+            if peek(1) == "("
+              if peek(2) == "("
+                skip_arithmetic_substitution
+              else
+                skip_command_substitution
+              end
+            else
+              advance
+            end
+          else
+            advance
+          end
+        end
+        raise ArgumentError, "Unmatched quote"
+      end
+
+      def skip_backtick
+        advance # opening backtick
+        until eof?
+          c = current_char
+          case c
+          when "\\"
+            advance_escape
+          when "`"
+            advance
+            return
+          when "$"
+            if peek(1) == "("
+              if peek(2) == "("
+                skip_arithmetic_substitution
+              else
+                skip_command_substitution
+              end
+            else
+              advance
+            end
+          else
+            advance
+          end
+        end
+        raise ArgumentError, "Unmatched backtick"
+      end
+
+      def skip_command_substitution
+        advance(2) # consume "$("
+        depth = 1
+
+        until eof?
+          c = current_char
+          case c
+          when "\\"
+            advance_escape
+          when "'"
+            skip_single_quoted
+          when "\""
+            skip_double_quoted
+          when "`"
+            skip_backtick
+          when "$"
+            if peek(1) == "("
+              if peek(2) == "("
+                skip_arithmetic_substitution
+              else
+                advance(2)
+                depth += 1
+              end
+            else
+              advance
+            end
+          when "("
+            advance
+            depth += 1
+          when ")"
+            advance
+            depth -= 1
+            return if depth.zero?
+          else
+            advance
+          end
+        end
+
+        raise ArgumentError, "Unmatched $(...)"
+      end
+
+      def skip_arithmetic_substitution
+        advance(3) # consume "$(("
+        depth = 1
+
+        until eof?
+          c = current_char
+          case c
+          when "\\"
+            advance_escape
+          when "'"
+            skip_single_quoted
+          when "\""
+            skip_double_quoted
+          when "`"
+            skip_backtick
+          when "$"
+            if peek(1) == "("
+              if peek(2) == "("
+                advance(3)
+                depth += 1
+              else
+                skip_command_substitution
+              end
+            else
+              advance
+            end
+          when ")"
+            if peek(1) == ")"
+              advance(2)
+              depth -= 1
+              return if depth.zero?
+            else
+              advance
+            end
+          else
+            advance
+          end
+        end
+
+        raise ArgumentError, "Unmatched $((...))"
+      end
+
+      def read_escape
+        start = index
+        advance_escape
+        @line[start...index]
+      end
+
+      def read_single_quoted
+        start = index
+        skip_single_quoted
+        @line[start...index]
+      end
+
+      def read_double_quoted
+        start = index
+        skip_double_quoted
+        @line[start...index]
+      end
+
+      def read_backtick
+        start = index
+        skip_backtick
+        @line[start...index]
+      end
+
+      def read_arithmetic_substitution
+        start = index
+        skip_arithmetic_substitution
+        @line[start...index]
+      end
+    end
+
+    class << self
+      def split_commands(line)
+        commands = []
+        next_op = :always
+        tokens = Scanner.new(line).tokenize_command_list
+
+        tokens.each do |token|
+          case token.type
+          when :text
+            commands << {command: token.value, op: next_op}
+            if next_op == :and && token.value.strip.empty?
+              raise ArgumentError, "syntax error: expected command after `&&`"
+            end
+            next_op = :always
+          when :separator
+            if token.value == :and
+              if commands.empty? || commands.last[:command].strip.empty?
+                raise ArgumentError, "syntax error near unexpected token `&&`"
+              end
+              next_op = :and
+            else
+              next_op = :always
+            end
+          else
+            raise ArgumentError, "Unknown token type: #{token.type}"
+          end
+        end
+
+        commands
+      end
+
+      def read_dollar_paren(line, start_index)
+        Scanner.new(line, index: start_index).read_dollar_paren_body
+      end
     end
   end
 end
diff --git a/ruby/shell/word_expander.rb b/ruby/shell/word_expander.rb
index 9889289..b02308f 100644
--- a/ruby/shell/word_expander.rb
+++ b/ruby/shell/word_expander.rb
@@ -1,4 +1,3 @@
-require "shellwords"
 require "open3"
 require "shell/quote_cursor"
 require "shell/string_parser"
@@ -54,12 +53,12 @@ module Shell
         end
     end
 
-    # Lifted directly from Ruby 4.0.0.
+    # Adapted from Ruby's Shellwords splitting logic.
     #
     # Splits a string into an array of tokens in the same way the UNIX
     # Bourne shell does.
     #
-    #   argv = Shellwords.split('here are "two words"')
+    #   argv = shellsplit('here are "two words"')
     #   argv #=> ["here", "are", "two words"]
     #
     # +line+ must not contain NUL characters because of nature of
@@ -69,7 +68,7 @@ module Shell
     # metacharacters except for the single and double quotes and
     # backslash are not treated as such.
     #
-    #   argv = Shellwords.split('ruby my_prog.rb | less')
+    #   argv = shellsplit('ruby my_prog.rb | less')
     #   argv #=> ["ruby", "my_prog.rb", "|", "less"]
     #
     # String#shellsplit is a shortcut for this function.
diff --git a/ruby/test/shell_test.rb b/ruby/test/shell_test.rb
index fa8a141..41bcb03 100644
--- a/ruby/test/shell_test.rb
+++ b/ruby/test/shell_test.rb
@@ -93,6 +93,16 @@ class ShellTest < Minitest::Test
     assert_equal "hi", `#{A1_PATH} -c 'echo $(echo hi)'`.chomp
   end
 
+  def test_keeps_control_operators_inside_command_substitution
+    semicolon_stdout, semicolon_stderr, semicolon_status = Open3.capture3(A1_PATH, "-c", "echo $(echo hi; echo bye)")
+    assert semicolon_status.success?, semicolon_stderr
+    assert_equal "hi bye\n", semicolon_stdout
+
+    and_stdout, and_stderr, and_status = Open3.capture3(A1_PATH, "-c", "echo $(echo hi && echo bye)")
+    assert and_status.success?, and_stderr
+    assert_equal "hi bye\n", and_stdout
+  end
+
   def test_expands_command_substitution_with_escaped_quote
     assert_equal "a\"b", `#{A1_PATH} -c 'echo $(printf \"%s\" \"a\\\"b\")'`.chomp
   end