diff --git a/.gitignore b/.gitignore
index ea8c4bf..2c96eb1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
-/target
+target/
+Cargo.lock
diff --git a/Cargo.lock b/Cargo.lock
deleted file mode 100644
index ae03c9f..0000000
--- a/Cargo.lock
+++ /dev/null
@@ -1,32 +0,0 @@
-# This file is automatically @generated by Cargo.
-# It is not intended for manual editing.
-version = 3
-
-[[package]]
-name = "carter-emu"
-version = "0.1.0"
-dependencies = [
- "itertools",
- "pretty-hex",
-]
-
-[[package]]
-name = "either"
-version = "1.8.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "90e5c1c8368803113bf0c9584fc495a58b86dc8a29edbf8fe877d21d9507e797"
-
-[[package]]
-name = "itertools"
-version = "0.10.4"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d8bf247779e67a9082a4790b45e71ac7cfd1321331a5c856a74a9faebdab78d0"
-dependencies = [
- "either",
-]
-
-[[package]]
-name = "pretty-hex"
-version = "0.3.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c6fa0831dd7cc608c38a5e323422a0077678fa5744aa2be4ad91c4ece8eec8d5"
diff --git a/Cargo.toml b/Cargo.toml
index 87be82b..797c6f8 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -3,8 +3,13 @@ name = "carter-emu"
 version = "0.1.0"
 edition = "2021"
 
+[[bin]]
+name = "ce"
+path = "src/main.rs"
+
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-itertools = "*"
-pretty-hex = "*"
+itertools = "0.10.*"
+pretty-hex = "0.3.*"
+clap = {version = "3.2.*", features=["derive"]}
diff --git a/src/main.rs b/src/main.rs
index 6e1df33..89dac0c 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,18 +1,30 @@
+use clap::Parser;
 use itertools::Itertools;
 use pretty_hex::*;
-use std::env;
 use std::fs;
+use std::io::{stdin, Read};
+
+#[derive(Parser)]
+#[clap(version, about)]
+struct Args {
+    /// Path to file to execute
+    #[clap(value_parser)]
+    path: String,
+
+    /// Set debug level
+    /// -d for stepping
+    /// -dd for debug info at step
+    #[clap(short, action = clap::ArgAction::Count)]
+    debug: u8,
+}
 
 fn main() -> Result<(), std::io::Error> {
     println!("carter-emu v{}", env!("CARGO_PKG_VERSION"));
 
     // load program from file into memory
-    let args: Vec<String> = env::args().collect();
-    if args.len() < 2 {
-        panic!("usage: ce <filename>");
-    }
+    let args = Args::parse();
 
-    let mut in_bytes: Vec<u8> = fs::read(&args[1])?;
+    let mut in_bytes: Vec<u8> = fs::read(&args.path)?;
     in_bytes.pop(); // remove trailing newline
     let instructions = Instruction::from_chars(in_bytes.into_iter());
 
@@ -28,14 +40,14 @@ fn main() -> Result<(), std::io::Error> {
     }
     mem.resize(256, 0);
 
-    execute(&mut mem);
+    execute(&mut mem, args.debug);
 
     println!("{}", pretty_hex(&mem));
 
     Ok(())
 }
 
-fn execute(mem: &mut Vec<u8>) {
+fn execute(mem: &mut Vec<u8>, step: u8) {
     // prep registers
     let mut dp = 0; // data pointer
     let mut ipl = 0; // instruction pointer low
@@ -43,6 +55,8 @@ fn execute(mem: &mut Vec<u8>) {
     let mut rpl = 0; // return pointer low
     let mut rph = 0; // return pointer high
 
+    let mut stdin = stdin();
+
     loop {
         if ipl == 256 {
             return;
@@ -51,6 +65,15 @@ fn execute(mem: &mut Vec<u8>) {
 
         loop {
             let inst = ins[iph];
+
+            if step > 1 {
+                print_state(ipl, iph, dp, mem, rpl, rph);
+            }
+            if step > 0 {
+                println!(">>> {inst}");
+                let _ = stdin.read(&mut [0u8]).unwrap();
+            }
+
             match inst {
                 Instruction::LoopOpen => {
                     rpl = ipl;
@@ -85,6 +108,24 @@ fn execute(mem: &mut Vec<u8>) {
     }
 }
 
+fn print_state(ipl: usize, iph: usize, dp: usize, mem: &Vec<u8>, rpl: usize, rph: usize) {
+    println!(
+        "ipl: {:2X} = {}
+iph: {:2X}
+ dp: {:2X} = {:2X}
+rpl: {:2X} = {}
+rph: {:2X}",
+        ipl,
+        Instruction::display_byte(mem[ipl]),
+        iph,
+        dp,
+        mem[dp],
+        rpl,
+        Instruction::display_byte(mem[rpl]),
+        rph,
+    );
+}
+
 #[derive(Copy, Clone)]
 enum Instruction {
     LoopOpen,
@@ -110,7 +151,6 @@ impl fmt::Display for Instruction {
 }
 
 impl Instruction {
-    #[allow(dead_code)]
     fn from_byte(byte: u8) -> Vec<Instruction> {
         // split into 2-bit pairs before mapping
         [
@@ -156,4 +196,9 @@ impl Instruction {
             | Instruction::to_pair(is.get(2)) << 2
             | Instruction::to_pair(is.get(3))
     }
+
+    fn display_byte(byte: u8) -> String {
+        let is = Instruction::from_byte(byte);
+        format!("{} {} {} {}", is[0], is[1], is[2], is[3])
+    }
 }