diff --git a/totalstations.py b/totalstations.py
index 57d6468..79859a6 100644
--- a/totalstations.py
+++ b/totalstations.py
@@ -920,19 +920,54 @@ def parse_next(self):
     """
         unit test
     """
-    ts = Idex('samples/test.idx')
-    #ts = Dump('samples/xxx.dmp')
-    #ts = SurvCE('samples/EBO-1739.rw5')
-    #ts = Stonex('samples/PAJE2OB.DAT')
-    #ts = LeicaGsi('samples/tata3.gsi', ' ')
-    #ts = JobAre('samples/test1.job', '=')
-    #ts = Sdr('samples/PAJE04.crd', None)
+    import sys
+    import os
+    
+    if len(sys.argv) > 1:
+        # maps extensions to classes; first item in list is the class
+        # and second, if present, is second argument for class 
+        # constructor
+        ext2class = {
+            '.idx': [Idex],
+            '.dmp': [Dump],
+            '.rw5': [SurvCE],
+            '.dat': [Stonex],
+            '.gsi': [LeicaGsi, ' '],
+            '.job': [JobAre, '='],
+            '.crd': [Sdr, None]
+        }
+        # find the class 
+        try:
+            toexec = ext2class[os.path.splitext(sys.argv[1])[1].lower()]
+        except KeyError:
+            print 'Unknown extension for file', sys.argv[1]
+            sys.exit(1)
+        
+        if len(sys.argv) == 3:
+            # the user may provide an argument to pass to the class
+            ts = toexec[0](sys.argv[1], sys.argv[2])
+        elif len(toexec) == 1:
+            # no default for second argument
+            ts = toexec[0](sys.argv[1])
+        else:
+            # there is a default second argument
+            ts = toexec[0](sys.argv[1], toexec[1])
+    else:
+        ts = Idex('samples/test.idx')
+        #ts = Dump('samples/xxx.dmp')
+        #ts = SurvCE('samples/EBO-1739.rw5')
+        #ts = Stonex('samples/PAJE2OB.DAT')
+        #ts = LeicaGsi('samples/tata3.gsi', ' ')
+        #ts = JobAre('samples/test1.job', '=')
+        #ts = Sdr('samples/PAJE04.crd', None)
+    
     if ts.open() != 0:
         print "Open error"
-    while True:
-        r = ts.parse_next()
-        if r is None:
-            break
-        if len(r) > 0:
-            print r
-    ts.close()
+    else:
+        while True:
+            r = ts.parse_next()
+            if r is None:
+                break
+            if len(r) > 0:
+                print r
+        ts.close()