implement '--clear-cache'

Effectively clears all cached values from the cache database by
executing "DELETE FROM data" without any further user input.

gallery_dl/__init__.py

@@ -181,6 +181,18 @@ def main():
                 if test:
                     print("Example :", test[0])
                 print()
+        elif args.clear_cache:
+            from . import cache
+            log = logging.getLogger("cache")
+            cnt = cache.clear()
+
+            if cnt is None:
+                log.error("Database file not available")
+            else:
+                log.info(
+                    "Deleted %d %s from '%s'",
+                    cnt, "entry" if cnt == 1 else "entries", cache._path(),
+                )
         else:
             if not args.urls and not args.inputfile:
                 parser.error(

gallery_dl/cache.py

@@ -166,19 +166,39 @@ def cache(maxage=3600, keyarg=None):
     return wrap
 
 
-try:
-    path = config.get(("cache", "file"), "")
-    if path is None:
-        raise RuntimeError()
-    elif not path:
+def clear():
+    """Delete all database entries"""
+    db = DatabaseCacheDecorator.db
+
+    if db:
+        rowcount = 0
+        cursor = db.cursor()
+        try:
+            cursor.execute("DELETE FROM data")
+        except sqlite3.OperationalError:
+            pass  # database is not initialized,  can't be modified, etc.
+        else:
+            rowcount = cursor.rowcount
+            db.commit()
+            cursor.execute("VACUUM")
+        return rowcount
+
+    return None
+
+
+def _path():
+    path = config.get(("cache", "file"), -1)
+
+    if path == -1:
         import tempfile
         import os.path
-        path = os.path.join(tempfile.gettempdir(), ".gallery-dl.cache")
-    else:
-        path = util.expand_path(path)
+        return os.path.join(tempfile.gettempdir(), ".gallery-dl.cache")
 
+    return util.expand_path(path)
+
+
+try:
     DatabaseCacheDecorator.db = sqlite3.connect(
-        path, timeout=30, check_same_thread=False)
-
-except (RuntimeError, sqlite3.OperationalError):
+        _path(), timeout=30, check_same_thread=False)
+except (TypeError, sqlite3.OperationalError):
     cache = memcache  # noqa: F811

gallery_dl/option.py

@@ -93,6 +93,11 @@ def build_parser():
         metavar="URL", action=ConfigAction, dest="proxy",
         help="Use the specified proxy",
     )
+    general.add_argument(
+        "--clear-cache",
+        dest="clear_cache", action="store_true",
+        help="Delete all cached login sessions, cookies, etc.",
+    )
 
     output = parser.add_argument_group("Output Options")
     output.add_argument(