diff --git a/applegpu.py b/applegpu.py
index a84e4b9..c19c224 100644
--- a/applegpu.py
+++ b/applegpu.py
@@ -1595,14 +1595,11 @@ def encode_string(self, fields, opstr):
 				value = try_parse_integer(s[2:])
 				if value is not None:
 					masked = value & ((1 << self.size) - 1)
-					print('value', value, hex(masked))
 					if value != sign_extend(masked, self.size):
 						raise Exception('out of range BranchOffsetDesc %r' % (opstr,))
 					fields[self.name] = masked
-					print(fields)
 					return
 
-		# TODO: labels, somehow
 		raise Exception('invalid BranchOffsetDesc %r' % (opstr,))
 
 
diff --git a/assemble.py b/assemble.py
index 1e58446..695186c 100644
--- a/assemble.py
+++ b/assemble.py
@@ -1,7 +1,6 @@
 import sys
 import applegpu
-
-# TODO: labels, file i/o
+import disassemble
 
 def begin_encoding(mnem, operand_strings):
 	for o in applegpu.instruction_descriptors:
@@ -34,12 +33,83 @@ def assemble_line(line):
 
 	return idesc.to_bytes(n)
 
+def assemble_multiline(lines, print_asm=False):
+	seen_labels = {}
+	awaiting_labels = {}
+	output = bytearray()
+	try:
+		for line in lines:
+			line = line.strip()
+			if ':' in line and not ' ' in line[:line.index(':')]:
+				index = line.index(':')
+				label = line[:index].strip()
+				line = line[index+1:].strip()
+				pc = seen_labels[label] = len(output)
+				if label in awaiting_labels:
+					for (target, offset, size, text) in awaiting_labels[label]:
+						asm = assemble_line(text.replace(f'pc+{label}', f'pc+{pc-offset}'))
+						if len(asm) != size:
+							raise ValueError(f'Instruction "{text}" was a different size before setting the label vs after ({len(asm)} != {size})')
+						output[offset:offset+size] = asm
+					del awaiting_labels[label]
+			if not line:
+				continue
+			if 'pc+' in line and not line[line.index('pc+') + 3].isdigit():
+				index = line.index('pc+')
+				label = line[index + 3:].partition(',')[0]
+				if ' ' in label:
+					raise ValueError(f'Bad label "{label}" (cannot contain spaces)')
+				offset = len(output)
+				if label in seen_labels:
+					output.extend(assemble_line(line.replace(f'pc+{label}', f'pc-{offset-seen_labels[label]}')))
+				else:
+					asm = assemble_line(line.replace(f'pc+{label}', 'pc+0'))
+					if not label in awaiting_labels:
+						awaiting_labels[label] = []
+					awaiting_labels[label].append((label, offset, len(asm), line))
+					output.extend(asm)
+			else:
+				output.extend(assemble_line(line))
+	finally:
+		if print_asm:
+			disassemble.disassemble(output)
+	if awaiting_labels:
+		missing = ', '.join(awaiting_labels.keys())
+		raise ValueError(f'Missing required labels: {missing}')
+	return output
+
+
 if __name__ == '__main__':
+	def printUsageAndExit():
+		print('Usage: python3 asssemble.py ([instruction text separated by semicolons] | -i ifile.S [-o ofile.bin] [-quiet])')
+		exit(1)
 	if len(sys.argv) > 1:
-		inp = ' '.join(sys.argv[1:]).split(';')
-		for line in inp:
-			asm_bytes = assemble_line(line)
-			print(asm_bytes.hex().ljust(32), applegpu.disassemble_bytes(asm_bytes))
+		if sys.argv[1].startswith('-'):
+			args = sys.argv[1:]
+			ifile = None
+			ofile = None
+			quiet = False
+			while args:
+				arg = args.pop(0)
+				if arg == '-i':
+					ifile = args.pop(0)
+				elif arg == '-o':
+					ofile = args.pop(0)
+				elif arg == '-quiet':
+					quiet = True
+				else:
+					print(f'Unrecognized argument {arg}')
+					printUsageAndExit()
+			if not ifile:
+				print('Input file required')
+				printUsageAndExit()
+			with open(ifile, 'r') as file:
+				asm = assemble_multiline(file, print_asm=not quiet)
+			if ofile:
+				with open(ofile, 'wb') as file:
+					file.write(asm)
+		else:
+			inp = ' '.join(sys.argv[1:]).split(';')
+			assemble_multiline(inp, print_asm=True)
 	else:
-		print('usage: python3 asssemble.py [instruction text separated by semicolons]')
-		exit(1)
+		printUsageAndExit()