A couple of script changes after CI integration

- Renamed struct_.py -> structs.py again.

- Removed lfs.csv, instead prefering script specific csv files.

- Added *-diff make rules for quick comparison against a previous
  result, results are now implicitly written on each run.

  For example, `make code` creates lfs.code.csv and prints the summary, which
  can be followed by `make code-diff` to compare changes against the saved
  lfs.code.csv without overwriting.

- Added nargs=? support for -s and -S, now uses a per-result _sort
  attribute to decide sort if fields are unspecified.

8 files changed, 175 insertions, 84 deletions

diff --git a/scripts/code.py b/scripts/code.py
index 6769cbd..ba8bd1e 100755
--- a/scripts/code.py
+++ b/scripts/code.py
@@ -112,6 +112,7 @@ class CodeResult(co.namedtuple('CodeResult', [
         'size'])):
     _by = ['file', 'function']
     _fields = ['size']
+    _sort = ['size']
     _types = {'size': Int}
 
     __slots__ = ()
@@ -385,8 +386,12 @@ def table(Result, results, diff_results=None, *,
             reverse=True)
     if sort:
         for k, reverse in reversed(sort):
-            names.sort(key=lambda n: (getattr(table[n], k),)
-                if getattr(table.get(n), k, None) is not None else (),
+            names.sort(
+                key=lambda n: tuple(
+                    (getattr(table[n], k),)
+                    if getattr(table.get(n), k, None) is not None else ()
+                    for k in ([k] if k else [
+                        k for k in Result._sort if k in fields])),
                 reverse=reverse ^ (not k or k in Result._fields))
 
 
@@ -544,8 +549,10 @@ def main(obj_paths, *,
     results.sort()
     if sort:
         for k, reverse in reversed(sort):
-            results.sort(key=lambda r: (getattr(r, k),)
-                if getattr(r, k) is not None else (),
+            results.sort(
+                key=lambda r: tuple(
+                    (getattr(r, k),) if getattr(r, k) is not None else ()
+                    for k in ([k] if k else CodeResult._sort)),
                 reverse=reverse ^ (not k or k in CodeResult._fields))
 
     # write results to CSV
@@ -553,14 +560,15 @@ def main(obj_paths, *,
         with openio(args['output'], 'w') as f:
             writer = csv.DictWriter(f,
                 (by if by is not None else CodeResult._by)
-                + ['code_'+k for k in CodeResult._fields])
+                + ['code_'+k for k in (
+                    fields if fields is not None else CodeResult._fields)])
             writer.writeheader()
             for r in results:
                 writer.writerow(
-                    {k: getattr(r, k)
-                        for k in (by if by is not None else CodeResult._by)}
-                    | {'code_'+k: getattr(r, k)
-                        for k in CodeResult._fields})
+                    {k: getattr(r, k) for k in (
+                        by if by is not None else CodeResult._by)}
+                    | {'code_'+k: getattr(r, k) for k in (
+                        fields if fields is not None else CodeResult._fields)})
 
     # find previous results?
     if args.get('diff'):
@@ -655,12 +663,14 @@ if __name__ == "__main__":
             namespace.sort.append((value, True if option == '-S' else False))
     parser.add_argument(
         '-s', '--sort',
+        nargs='?',
         action=AppendSort,
-        help="Sort by this fields.")
+        help="Sort by this field.")
     parser.add_argument(
         '-S', '--reverse-sort',
+        nargs='?',
         action=AppendSort,
-        help="Sort by this fields, but backwards.")
+        help="Sort by this field, but backwards.")
     parser.add_argument(
         '-Y', '--summary',
         action='store_true',
diff --git a/scripts/cov.py b/scripts/cov.py
index e6a7d63..b61b2e5 100755
--- a/scripts/cov.py
+++ b/scripts/cov.py
@@ -180,6 +180,7 @@ class CovResult(co.namedtuple('CovResult', [
         'calls', 'hits', 'funcs', 'lines', 'branches'])):
     _by = ['file', 'function', 'line']
     _fields = ['calls', 'hits', 'funcs', 'lines', 'branches']
+    _sort = ['funcs', 'lines', 'branches', 'hits', 'calls']
     _types = {
         'calls': Int, 'hits': Int,
         'funcs': Frac, 'lines': Frac, 'branches': Frac}
@@ -372,8 +373,12 @@ def table(Result, results, diff_results=None, *,
             reverse=True)
     if sort:
         for k, reverse in reversed(sort):
-            names.sort(key=lambda n: (getattr(table[n], k),)
-                if getattr(table.get(n), k, None) is not None else (),
+            names.sort(
+                key=lambda n: tuple(
+                    (getattr(table[n], k),)
+                    if getattr(table.get(n), k, None) is not None else ()
+                    for k in ([k] if k else [
+                        k for k in Result._sort if k in fields])),
                 reverse=reverse ^ (not k or k in Result._fields))
 
 
@@ -617,8 +622,10 @@ def main(gcda_paths, *,
     results.sort()
     if sort:
         for k, reverse in reversed(sort):
-            results.sort(key=lambda r: (getattr(r, k),)
-                if getattr(r, k) is not None else (),
+            results.sort(
+                key=lambda r: tuple(
+                    (getattr(r, k),) if getattr(r, k) is not None else ()
+                    for k in ([k] if k else CovResult._sort)),
                 reverse=reverse ^ (not k or k in CovResult._fields))
 
     # write results to CSV
@@ -626,14 +633,15 @@ def main(gcda_paths, *,
         with openio(args['output'], 'w') as f:
             writer = csv.DictWriter(f,
                 (by if by is not None else CovResult._by)
-                + ['cov_'+k for k in CovResult._fields])
+                + ['cov_'+k for k in (
+                    fields if fields is not None else CovResult._fields)])
             writer.writeheader()
             for r in results:
                 writer.writerow(
-                    {k: getattr(r, k)
-                        for k in (by if by is not None else CovResult._by)}
-                    | {'cov_'+k: getattr(r, k)
-                        for k in CovResult._fields})
+                    {k: getattr(r, k) for k in (
+                        by if by is not None else CovResult._by)}
+                    | {'cov_'+k: getattr(r, k) for k in (
+                        fields if fields is not None else CovResult._fields)})
 
     # find previous results?
     if args.get('diff'):
@@ -748,10 +756,12 @@ if __name__ == "__main__":
             namespace.sort.append((value, True if option == '-S' else False))
     parser.add_argument(
         '-s', '--sort',
+        nargs='?',
         action=AppendSort,
         help="Sort by this field.")
     parser.add_argument(
         '-S', '--reverse-sort',
+        nargs='?',
         action=AppendSort,
         help="Sort by this field, but backwards.")
     parser.add_argument(
diff --git a/scripts/data.py b/scripts/data.py
index 102059b..e9770aa 100755
--- a/scripts/data.py
+++ b/scripts/data.py
@@ -112,6 +112,7 @@ class DataResult(co.namedtuple('DataResult', [
         'size'])):
     _by = ['file', 'function']
     _fields = ['size']
+    _sort = ['size']
     _types = {'size': Int}
 
     __slots__ = ()
@@ -385,8 +386,12 @@ def table(Result, results, diff_results=None, *,
             reverse=True)
     if sort:
         for k, reverse in reversed(sort):
-            names.sort(key=lambda n: (getattr(table[n], k),)
-                if getattr(table.get(n), k, None) is not None else (),
+            names.sort(
+                key=lambda n: tuple(
+                    (getattr(table[n], k),)
+                    if getattr(table.get(n), k, None) is not None else ()
+                    for k in ([k] if k else [
+                        k for k in Result._sort if k in fields])),
                 reverse=reverse ^ (not k or k in Result._fields))
 
 
@@ -541,8 +546,10 @@ def main(obj_paths, *,
     results.sort()
     if sort:
         for k, reverse in reversed(sort):
-            results.sort(key=lambda r: (getattr(r, k),)
-                if getattr(r, k) is not None else (),
+            results.sort(
+                key=lambda r: tuple(
+                    (getattr(r, k),) if getattr(r, k) is not None else ()
+                    for k in ([k] if k else DataResult._sort)),
                 reverse=reverse ^ (not k or k in DataResult._fields))
 
     # write results to CSV
@@ -550,14 +557,15 @@ def main(obj_paths, *,
         with openio(args['output'], 'w') as f:
             writer = csv.DictWriter(f,
                 (by if by is not None else DataResult._by)
-                + ['data_'+k for k in DataResult._fields])
+                + ['data_'+k for k in (
+                    fields if fields is not None else DataResult._fields)])
             writer.writeheader()
             for r in results:
                 writer.writerow(
-                    {k: getattr(r, k)
-                        for k in (by if by is not None else DataResult._by)}
-                    | {'data_'+k: getattr(r, k)
-                        for k in DataResult._fields})
+                    {k: getattr(r, k) for k in (
+                        by if by is not None else DataResult._by)}
+                    | {'data_'+k: getattr(r, k) for k in (
+                        fields if fields is not None else DataResult._fields)})
 
     # find previous results?
     if args.get('diff'):
@@ -652,12 +660,14 @@ if __name__ == "__main__":
             namespace.sort.append((value, True if option == '-S' else False))
     parser.add_argument(
         '-s', '--sort',
+        nargs='?',
         action=AppendSort,
-        help="Sort by this fields.")
+        help="Sort by this field.")
     parser.add_argument(
         '-S', '--reverse-sort',
+        nargs='?',
         action=AppendSort,
-        help="Sort by this fields, but backwards.")
+        help="Sort by this field, but backwards.")
     parser.add_argument(
         '-Y', '--summary',
         action='store_true',
diff --git a/scripts/perf.py b/scripts/perf.py
index b644858..2ee006c 100755
--- a/scripts/perf.py
+++ b/scripts/perf.py
@@ -122,6 +122,7 @@ class PerfResult(co.namedtuple('PerfResult', [
         'children'])):
     _by = ['file', 'function', 'line']
     _fields = ['cycles', 'bmisses', 'branches', 'cmisses', 'caches']
+    _sort = ['cycles', 'bmisses', 'cmisses', 'branches', 'caches']
     _types = {
         'cycles': Int,
         'bmisses': Int, 'branches': Int,
@@ -712,10 +713,15 @@ def table(Result, results, diff_results=None, *,
             reverse=True)
     if sort:
         for k, reverse in reversed(sort):
-            names.sort(key=lambda n: (getattr(table[n], k),)
-                if getattr(table.get(n), k, None) is not None else (),
+            names.sort(
+                key=lambda n: tuple(
+                    (getattr(table[n], k),)
+                    if getattr(table.get(n), k, None) is not None else ()
+                    for k in ([k] if k else [
+                        k for k in Result._sort if k in fields])),
                 reverse=reverse ^ (not k or k in Result._fields))
 
+
     # build up our lines
     lines = []
 
@@ -853,8 +859,13 @@ def table(Result, results, diff_results=None, *,
             names_.sort()
             if sort:
                 for k, reverse in reversed(sort):
-                    names_.sort(key=lambda n: (getattr(table_[n], k),)
-                        if getattr(table_.get(n), k, None) is not None else (),
+                    names_.sort(
+                        key=lambda n: tuple(
+                            (getattr(table_[n], k),)
+                            if getattr(table_.get(n), k, None) is not None
+                            else ()
+                            for k in ([k] if k else [
+                                k for k in Result._sort if k in fields])),
                         reverse=reverse ^ (not k or k in Result._fields))
 
             for i, name in enumerate(names_):
@@ -1051,8 +1062,10 @@ def report(perf_paths, *,
     results.sort()
     if sort:
         for k, reverse in reversed(sort):
-            results.sort(key=lambda r: (getattr(r, k),)
-                if getattr(r, k) is not None else (),
+            results.sort(
+                key=lambda r: tuple(
+                    (getattr(r, k),) if getattr(r, k) is not None else ()
+                    for k in ([k] if k else PerfResult._sort)),
                 reverse=reverse ^ (not k or k in PerfResult._fields))
 
     # write results to CSV
@@ -1060,14 +1073,15 @@ def report(perf_paths, *,
         with openio(args['output'], 'w') as f:
             writer = csv.DictWriter(f,
                 (by if by is not None else PerfResult._by)
-                + ['perf_'+k for k in PerfResult._fields])
+                + ['perf_'+k for k in (
+                    fields if fields is not None else PerfResult._fields)])
             writer.writeheader()
             for r in results:
                 writer.writerow(
-                    {k: getattr(r, k)
-                        for k in (by if by is not None else PerfResult._by)}
-                    | {'perf_'+k: getattr(r, k)
-                        for k in PerfResult._fields})
+                    {k: getattr(r, k) for k in (
+                        by if by is not None else PerfResult._by)}
+                    | {'perf_'+k: getattr(r, k) for k in (
+                        fields if fields is not None else PerfResult._fields)})
 
     # find previous results?
     if args.get('diff'):
@@ -1192,12 +1206,14 @@ if __name__ == "__main__":
             namespace.sort.append((value, True if option == '-S' else False))
     parser.add_argument(
         '-s', '--sort',
+        nargs='?',
         action=AppendSort,
-        help="Sort by this fields.")
+        help="Sort by this field.")
     parser.add_argument(
         '-S', '--reverse-sort',
+        nargs='?',
         action=AppendSort,
-        help="Sort by this fields, but backwards.")
+        help="Sort by this field, but backwards.")
     parser.add_argument(
         '-Y', '--summary',
         action='store_true',
diff --git a/scripts/perfbd.py b/scripts/perfbd.py
index 3a43101..bf57f60 100755
--- a/scripts/perfbd.py
+++ b/scripts/perfbd.py
@@ -113,6 +113,7 @@ class PerfBdResult(co.namedtuple('PerfBdResult', [
         'children'])):
     _by = ['file', 'function', 'line']
     _fields = ['readed', 'proged', 'erased']
+    _sort = ['erased', 'proged', 'readed']
     _types = {'readed': Int, 'proged': Int, 'erased': Int}
 
     __slots__ = ()
@@ -678,10 +679,15 @@ def table(Result, results, diff_results=None, *,
             reverse=True)
     if sort:
         for k, reverse in reversed(sort):
-            names.sort(key=lambda n: (getattr(table[n], k),)
-                if getattr(table.get(n), k, None) is not None else (),
+            names.sort(
+                key=lambda n: tuple(
+                    (getattr(table[n], k),)
+                    if getattr(table.get(n), k, None) is not None else ()
+                    for k in ([k] if k else [
+                        k for k in Result._sort if k in fields])),
                 reverse=reverse ^ (not k or k in Result._fields))
 
+
     # build up our lines
     lines = []
 
@@ -819,8 +825,13 @@ def table(Result, results, diff_results=None, *,
             names_.sort()
             if sort:
                 for k, reverse in reversed(sort):
-                    names_.sort(key=lambda n: (getattr(table_[n], k),)
-                        if getattr(table_.get(n), k, None) is not None else (),
+                    names_.sort(
+                        key=lambda n: tuple(
+                            (getattr(table_[n], k),)
+                            if getattr(table_.get(n), k, None) is not None
+                            else ()
+                            for k in ([k] if k else [
+                                k for k in Result._sort if k in fields])),
                         reverse=reverse ^ (not k or k in Result._fields))
 
             for i, name in enumerate(names_):
@@ -1031,8 +1042,10 @@ def report(obj_path='', trace_paths=[], *,
     results.sort()
     if sort:
         for k, reverse in reversed(sort):
-            results.sort(key=lambda r: (getattr(r, k),)
-                if getattr(r, k) is not None else (),
+            results.sort(
+                key=lambda r: tuple(
+                    (getattr(r, k),) if getattr(r, k) is not None else ()
+                    for k in ([k] if k else PerfBdResult._sort)),
                 reverse=reverse ^ (not k or k in PerfBdResult._fields))
 
     # write results to CSV
@@ -1040,14 +1053,15 @@ def report(obj_path='', trace_paths=[], *,
         with openio(args['output'], 'w') as f:
             writer = csv.DictWriter(f,
                 (by if by is not None else PerfBdResult._by)
-                + ['perfbd_'+k for k in PerfBdResult._fields])
+                + ['perfbd_'+k for k in (
+                    fields if fields is not None else PerfBdResult._fields)])
             writer.writeheader()
             for r in results:
                 writer.writerow(
-                    {k: getattr(r, k)
-                        for k in (by if by is not None else PerfBdResult._by)}
-                    | {'perfbd_'+k: getattr(r, k)
-                        for k in PerfBdResult._fields})
+                    {k: getattr(r, k) for k in (
+                        by if by is not None else PerfBdResult._by)}
+                    | {'perfbd_'+k: getattr(r, k) for k in (
+                        fields if fields is not None else PerfBdResult._fields)})
 
     # find previous results?
     if args.get('diff'):
@@ -1164,12 +1178,14 @@ if __name__ == "__main__":
             namespace.sort.append((value, True if option == '-S' else False))
     parser.add_argument(
         '-s', '--sort',
+        nargs='?',
         action=AppendSort,
-        help="Sort by this fields.")
+        help="Sort by this field.")
     parser.add_argument(
         '-S', '--reverse-sort',
+        nargs='?',
         action=AppendSort,
-        help="Sort by this fields, but backwards.")
+        help="Sort by this field, but backwards.")
     parser.add_argument(
         '-Y', '--summary',
         action='store_true',
diff --git a/scripts/stack.py b/scripts/stack.py
index cc78fe1..ba95433 100755
--- a/scripts/stack.py
+++ b/scripts/stack.py
@@ -102,6 +102,7 @@ class StackResult(co.namedtuple('StackResult', [
         'file', 'function', 'frame', 'limit', 'children'])):
     _by = ['file', 'function']
     _fields = ['frame', 'limit']
+    _sort = ['limit', 'frame']
     _types = {'frame': Int, 'limit': Int}
 
     __slots__ = ()
@@ -350,8 +351,12 @@ def table(Result, results, diff_results=None, *,
             reverse=True)
     if sort:
         for k, reverse in reversed(sort):
-            names.sort(key=lambda n: (getattr(table[n], k),)
-                if getattr(table.get(n), k, None) is not None else (),
+            names.sort(
+                key=lambda n: tuple(
+                    (getattr(table[n], k),)
+                    if getattr(table.get(n), k, None) is not None else ()
+                    for k in ([k] if k else [
+                        k for k in Result._sort if k in fields])),
                 reverse=reverse ^ (not k or k in Result._fields))
 
 
@@ -569,8 +574,10 @@ def main(ci_paths,
     results.sort()
     if sort:
         for k, reverse in reversed(sort):
-            results.sort(key=lambda r: (getattr(r, k),)
-                if getattr(r, k) is not None else (),
+            results.sort(
+                key=lambda r: tuple(
+                    (getattr(r, k),) if getattr(r, k) is not None else ()
+                    for k in ([k] if k else StackResult._sort)),
                 reverse=reverse ^ (not k or k in StackResult._fields))
 
     # write results to CSV
@@ -578,14 +585,15 @@ def main(ci_paths,
         with openio(args['output'], 'w') as f:
             writer = csv.DictWriter(f,
                 (by if by is not None else StackResult._by)
-                + ['stack_'+k for k in StackResult._fields])
+                + ['stack_'+k for k in (
+                    fields if fields is not None else StackResult._fields)])
             writer.writeheader()
             for r in results:
                 writer.writerow(
-                    {k: getattr(r, k)
-                        for k in (by if by is not None else StackResult._by)}
-                    | {'stack_'+k: getattr(r, k)
-                        for k in StackResult._fields})
+                    {k: getattr(r, k) for k in (
+                        by if by is not None else StackResult._by)}
+                    | {'stack_'+k: getattr(r, k) for k in (
+                        fields if fields is not None else StackResult._fields)})
 
     # find previous results?
     if args.get('diff'):
@@ -685,12 +693,14 @@ if __name__ == "__main__":
             namespace.sort.append((value, True if option == '-S' else False))
     parser.add_argument(
         '-s', '--sort',
+        nargs='?',
         action=AppendSort,
-        help="Sort by this fields.")
+        help="Sort by this field.")
     parser.add_argument(
         '-S', '--reverse-sort',
+        nargs='?',
         action=AppendSort,
-        help="Sort by this fields, but backwards.")
+        help="Sort by this field, but backwards.")
     parser.add_argument(
         '-Y', '--summary',
         action='store_true',
diff --git a/scripts/struct_.py b/scripts/structs.py
index 8897db6..e9b97e7 100755
--- a/scripts/struct_.py
+++ b/scripts/structs.py
@@ -3,7 +3,7 @@
 # Script to find struct sizes.
 #
 # Example:
-# ./scripts/struct_.py lfs.o lfs_util.o -Ssize
+# ./scripts/structs.py lfs.o lfs_util.o -Ssize
 #
 # Copyright (c) 2022, The littlefs authors.
 # SPDX-License-Identifier: BSD-3-Clause
@@ -106,6 +106,7 @@ class Int(co.namedtuple('Int', 'x')):
 class StructResult(co.namedtuple('StructResult', ['file', 'struct', 'size'])):
     _by = ['file', 'struct']
     _fields = ['size']
+    _sort = ['size']
     _types = {'size': Int}
 
     __slots__ = ()
@@ -333,8 +334,12 @@ def table(Result, results, diff_results=None, *,
             reverse=True)
     if sort:
         for k, reverse in reversed(sort):
-            names.sort(key=lambda n: (getattr(table[n], k),)
-                if getattr(table.get(n), k, None) is not None else (),
+            names.sort(
+                key=lambda n: tuple(
+                    (getattr(table[n], k),)
+                    if getattr(table.get(n), k, None) is not None else ()
+                    for k in ([k] if k else [
+                        k for k in Result._sort if k in fields])),
                 reverse=reverse ^ (not k or k in Result._fields))
 
 
@@ -494,8 +499,10 @@ def main(obj_paths, *,
     results.sort()
     if sort:
         for k, reverse in reversed(sort):
-            results.sort(key=lambda r: (getattr(r, k),)
-                if getattr(r, k) is not None else (),
+            results.sort(
+                key=lambda r: tuple(
+                    (getattr(r, k),) if getattr(r, k) is not None else ()
+                    for k in ([k] if k else StructResult._sort)),
                 reverse=reverse ^ (not k or k in StructResult._fields))
 
     # write results to CSV
@@ -503,14 +510,15 @@ def main(obj_paths, *,
         with openio(args['output'], 'w') as f:
             writer = csv.DictWriter(f,
                 (by if by is not None else StructResult._by)
-                + ['struct_'+k for k in StructResult._fields])
+                + ['struct_'+k for k in (
+                    fields if fields is not None else StructResult._fields)])
             writer.writeheader()
             for r in results:
                 writer.writerow(
-                    {k: getattr(r, k)
-                        for k in (by if by is not None else StructResult._by)}
-                    | {'struct_'+k: getattr(r, k)
-                        for k in StructResult._fields})
+                    {k: getattr(r, k) for k in (
+                        by if by is not None else StructResult._by)}
+                    | {'struct_'+k: getattr(r, k) for k in (
+                        fields if fields is not None else StructResult._fields)})
 
     # find previous results?
     if args.get('diff'):
@@ -607,10 +615,12 @@ if __name__ == "__main__":
             namespace.sort.append((value, True if option == '-S' else False))
     parser.add_argument(
         '-s', '--sort',
+        nargs='?',
         action=AppendSort,
         help="Sort by this field.")
     parser.add_argument(
         '-S', '--reverse-sort',
+        nargs='?',
         action=AppendSort,
         help="Sort by this field, but backwards.")
     parser.add_argument(
diff --git a/scripts/summary.py b/scripts/summary.py
index 3d1e226..445368e 100755
--- a/scripts/summary.py
+++ b/scripts/summary.py
@@ -339,6 +339,7 @@ def infer(results, *,
         '__getattribute__': __getattribute__,
         '_by': by,
         '_fields': fields,
+        '_sort': fields,
         '_types': types_,
     })
 
@@ -419,8 +420,12 @@ def table(Result, results, diff_results=None, *,
             reverse=True)
     if sort:
         for k, reverse in reversed(sort):
-            names.sort(key=lambda n: (getattr(table[n], k),)
-                if getattr(table.get(n), k, None) is not None else (),
+            names.sort(
+                key=lambda n: tuple(
+                    (getattr(table[n], k),)
+                    if getattr(table.get(n), k, None) is not None else ()
+                    for k in ([k] if k else [
+                        k for k in Result._sort if k in fields])),
                 reverse=reverse ^ (not k or k in Result._fields))
 
 
@@ -649,8 +654,10 @@ def main(csv_paths, *,
     results.sort()
     if sort:
         for k, reverse in reversed(sort):
-            results.sort(key=lambda r: (getattr(r, k),)
-                if getattr(r, k) is not None else (),
+            results.sort(
+                key=lambda r: tuple(
+                    (getattr(r, k),) if getattr(r, k) is not None else ()
+                    for k in ([k] if k else Result._sort)),
                 reverse=reverse ^ (not k or k in Result._fields))
 
     # write results to CSV
@@ -761,12 +768,14 @@ if __name__ == "__main__":
             namespace.sort.append((value, True if option == '-S' else False))
     parser.add_argument(
         '-s', '--sort',
+        nargs='?',
         action=AppendSort,
-        help="Sort by this fields.")
+        help="Sort by this field.")
     parser.add_argument(
         '-S', '--reverse-sort',
+        nargs='?',
         action=AppendSort,
-        help="Sort by this fields, but backwards.")
+        help="Sort by this field, but backwards.")
     parser.add_argument(
         '-Y', '--summary',
         action='store_true',