diff --git a/src/argparser b/src/argparser
index 216cdca..86e16a9 160000
--- a/src/argparser
+++ b/src/argparser
@@ -1 +1 @@
-Subproject commit 216cdcae53e86d6908aa1b4d86549b1ca5e7bb53
+Subproject commit 86e16a9855901b96d09d613f431fd7ee4690c6af
diff --git a/src/assembler.js b/src/assembler.js
index 484546d..709740e 100755
--- a/src/assembler.js
+++ b/src/assembler.js
@@ -2,6 +2,7 @@
 
 const fs = require('fs');
 
+const argparser = require('./argparser/argparser.js');
 const { logMemory } = require('./logging.js');
 const { num2hex, hex2num, bin2num } = require('./conversions.js');
 const DBG = require('./dbg.js');
@@ -406,14 +407,39 @@ function stripWhitespaceFromEnds(line) {
 
 // Initialize debugger
 let dbg = new DBG('nitpick');
-let returnOnStdout = true; // FIXME - set this using a CLI arg
-if (returnOnStdout) { dbg = new DBG('none'); }
 
-// Get input
-const filename = process.argv[2]; // FIXME - Get filename in a more robust way
-const outputFilename = process.argv[3]; // FIXME - Get filename in a more robust way
-const inputFile_str = fs.readFileSync(filename, 'utf8');
-assemble(inputFile_str, outputFilename);
+// Handle command-line options...
+const args = argparser(process.argv);
+dbg.d('args', args);
+
+if (typeof args.i === 'undefined' || args.i.length === 0) {
+  console.error('Input file required (-i prog.asm)');
+  process.exit();
+}
+const inputFilename = args.i[0];
+const inputFile_str = fs.readFileSync(inputFilename, 'utf8');
+
+if ('o' in args && args.o.length === 0) {
+  console.error('Missing output file name (-o prog.asm)');
+  process.exit();
+}
+
+let outputFilename = null;
+let returnOnStdout = 'o' in args ? false : true;
+if (!returnOnStdout) {
+  outputFilename = args.o[0];
+} else {
+  dbg = new DBG('none');
+}
+
+let outputWithMetadata = false;
+if ('d' in args || 'debug' in args) {
+  outputWithMetadata = true;
+}
+
+// TODO: maybe check for too many args?
+
+assemble(inputFile_str, outputFilename, outputWithMetadata);
 
 
 /**
@@ -422,8 +448,8 @@ assemble(inputFile_str, outputFilename);
  * both machine code and metadata is written to the output file.
  * Otherwise, a string of decimal numbers is written.
  * @arg {string} sourceCode - Source code to assemble
- * @arg {string} [outputFile='out.txt'] -  Output file for machine code (and optional metadata)
- * @arg {boolean} [includeMetadata=false] - Include metadata for use when debugging using the simulator?
+ * @arg {string} [outputFile] -  Output file for machine code (and optional metadata)
+ * @arg {boolean} [includeMetadata=false] - Include metadata when writing output to a file? (for use when debugging using the simulator)
  **/
 function assemble(sourceCode, outputFile='out.txt', includeMetadata=false) {
   const out = decodeInstructions(sourceCode);
@@ -431,10 +457,7 @@ function assemble(sourceCode, outputFile='out.txt', includeMetadata=false) {
   if (returnOnStdout) {
     const debugJSON = JSON.stringify(out);
     console.log(debugJSON);
-    return;
-  }
-
-  if (!includeMetadata) {
+  } else if (!includeMetadata) {
     const asciiMachineCode = out.machineCode.toString().replace(/,/g, ' ');
     fs.writeFileSync(outputFile, asciiMachineCode);
   } else {