diff --git a/2019/ruby/day_05.rb b/2019/ruby/day_05.rb
new file mode 100644
index 0000000..b6681a9
--- /dev/null
+++ b/2019/ruby/day_05.rb
@@ -0,0 +1,52 @@
+OPCODES = ARGF.read.split(?,).map(&:to_i)
+
+def run(memory)
+  pc = 0
+  loop do
+    instruction = memory[pc]
+    return if instruction == 99
+
+    p pc
+    a, b, c, opcode = instruction.to_s.rjust(5, ?0).scan(/^(0|1)(0|1)(0|1)(\d\d)$/)[0].map(&:to_i)
+    c = c.zero? ? memory[memory[pc+1]] : memory[pc+1]
+    b = b.zero? ? memory[memory[pc+2]] : memory[pc+2]
+    a = a.zero? ? memory[memory[pc+3]] : memory[pc+3]
+
+    case opcode
+    when 1
+      memory[memory[pc+3]] = c + b
+      pc += 4
+    when 2
+      memory[memory[pc+3]] = c * b
+      pc += 4
+    when 3
+      memory[memory[pc+1]] = 5
+      pc += 2
+    when 4
+      puts c
+      pc += 2
+    when 5
+      if c.nonzero?
+        pc = b
+      else
+        pc += 3
+      end
+    when 6
+      if c.zero?
+        pc = b
+      else
+        pc += 3
+      end
+    when 7
+      memory[memory[pc+3]] = (c < b) ? 1 : 0
+      pc += 4
+    when 8
+      memory[memory[pc+3]] = (c == b) ? 1 : 0
+      pc += 4
+    else
+      fail "unrecognized instruction: #{instruction}"
+    end
+  end
+end
+
+run(OPCODES)