diff --git a/cleanup-roster.py b/cleanup-roster.py
index b80e95a..4af123a 100644
--- a/cleanup-roster.py
+++ b/cleanup-roster.py
@@ -42,8 +42,11 @@ def     get_fields(self, fdno):
         else:
             return [self.fields[int(_)] for _ in fdno]
 
-def     write_csv(file, student_list, fields): 
-    csvwriter = csv.writer(file)
+def     write_csv(file, student_list, fields, nl = None): 
+    if nl is None:
+        csvwriter = csv.writer(file)
+    else:
+        csvwriter = csv.writer(file, lineterminator=nl)
     for s in student_list: 
         csvwriter.writerow(s.get_fields(fields))
 
@@ -51,9 +54,10 @@ def     write_csv(file, student_list, fields):
 parser.add_argument('infile', nargs='?', help='Input file.')
 parser.add_argument('-o', nargs='?', default='', const='', help='Output file.')
 parser.add_argument('-f', nargs='+', default='', help='List of field numbers.')
+parser.add_argument("-a", action='store_true', default=False, help='Append to the output file.')
 
 args = parser.parse_args()
-# print(args)
+print(args)
 
 student_list = []
 student = None
@@ -102,7 +106,10 @@ def     write_csv(file, student_list, fields):
     exit(1)
 
 if args.o != '':
-    with open(args.o, 'w', newline='') as csvfile:
+    flag = 'w'
+    if args.a:
+        flag = 'a+'
+    with open(args.o, flag, newline='') as csvfile:
         write_csv(csvfile, student_list, args.f)
 else:
-    write_csv(sys.stdout, student_list, args.f)
+    write_csv(sys.stdout, student_list, args.f, '\n')
diff --git a/readme.MD b/readme.MD
index 39b408f..31f6cc6 100644
--- a/readme.MD
+++ b/readme.MD
@@ -21,6 +21,8 @@ The `-o` option specifies an output file.
 python cleanup-roster.py downloaded.xls -o section1.csv
 ```
 
+The `-a` option specifies the append mode so the output file is not cleared.
+
 The `-f` option specifies the fields to be included. `all` 
 means all fields. Without `-f` option, only a few most useful
 fields are printed.
@@ -30,3 +32,8 @@ python cleanup-roster.py downloaded.xls -f 1 2
 python cleanup-roster.py downloaded.xls -f all
 ```
 
+In Powershell, the following command appends all students record to file all.csv.
+
+```
+dir *.xls | foreach { py .\cleanup-roster.py $_ -a -o all.csv }
+```