diff --git a/dummycharaviewer.py b/dummycharaviewer.py
index ad5e7b7..5779213 100755
--- a/dummycharaviewer.py
+++ b/dummycharaviewer.py
@@ -4,19 +4,17 @@
 import sys
 import struct
 
-
-source = sys.argv[-1]
 expected_magic_word = 0xdeadface
 
 
-def check_magic_word():
+def check_magic_word(dat_file):
     magic_word = struct.unpack("<L", dat_file.read(4))[0]
 
     if magic_word != expected_magic_word:
         print("Invalid Magic Word.")
 
 
-def read_character_name():
+def read_character_name(dat_file):
     name_length = struct.unpack("<L", dat_file.read(4))[0]
     name = (struct.unpack(f"<{name_length}s",
             dat_file.read(name_length))[0]).decode('UTF-8')
@@ -24,7 +22,7 @@ def read_character_name():
     print(f"Character’s Name: {name}")
 
 
-def read_filename():
+def read_filename(dat_file):
     filename_length = struct.unpack("<L", dat_file.read(4))[0]
     filename = (struct.unpack(f"<{filename_length}s",
                 dat_file.read(filename_length))[0]).decode('UTF-8')
@@ -32,9 +30,9 @@ def read_filename():
     print(f"Filename: {filename}")
 
 
-def read_coordinates():
+def read_coordinates(dat_file):
     coordinates = struct.unpack("<2H", dat_file.read(4))
-    x, y = coordinates[0], coordinates[1]
+    x, y = coordinates
 
     map_name_length = struct.unpack("<L", dat_file.read(4))[0]
     map_name = (struct.unpack(f"<{map_name_length}s",
@@ -43,8 +41,20 @@ def read_coordinates():
     print(f"Coordinates: {map_name} ({x},{y})")
 
 
-with open(source, "rb") as dat_file:
-    check_magic_word()
-    read_character_name()
-    read_filename()
-    read_coordinates()
+def main(argv):
+    """Main function."""
+    if len(argv) < 2:
+        print(f"Usage: {argv[0]} <dat_file>")
+        raise SystemExit(-1)
+
+    source = argv[1]
+    with open(source, "rb") as dat_file:
+        check_magic_word(dat_file)
+        read_character_name(dat_file)
+        read_filename(dat_file)
+        read_coordinates(dat_file)
+        raise SystemExit(0)
+
+
+if __name__ == "__main__":
+    main(sys.argv)