added a keep commandline switch (-k, --keep)

-keep output directory if keep commandline switch is provided
-added KEEP_OUTPUT_DIRECTORY to settings (default is to delete output
directory before processing)
-updated documentation

docs/settings.rst

@@ -52,6 +52,8 @@ Setting name              what it does ?
                           the default one ('main.css')
 `REVERSE_ARCHIVE_ORDER`   Reverse the archives order. (True makes it in
                           descending order: the newer first)
+`KEEP_OUTPUT_DIRECTORY`   Keep the output directory and just update all the generated files. 
+                          Default is to delete the output directory.   
 =======================   =======================================================
 
 Themes

pelican/__init__.py

@@ -9,7 +9,7 @@ from pelican.generators import (ArticlesGenerator, PagesGenerator,
 
 
 def init_params(settings=None, path=None, theme=None, output_path=None, 
-        markup=None):
+        markup=None, keep=False):
     """Read the settings, and performs some checks on the environment
     before doing anything else.
     """
@@ -25,6 +25,7 @@ def init_params(settings=None, path=None, theme=None, output_path=None,
     output_path = output_path or settings['OUTPUT_PATH']
     output_path = os.path.realpath(output_path)
     markup = markup or settings['MARKUP']
+    keep = keep or settings['KEEP_OUTPUT_DIRECTORY']
 
     # find the theme in pelican.theme if the given one does not exists
     if not os.path.exists(theme):
@@ -42,14 +43,14 @@ def init_params(settings=None, path=None, theme=None, output_path=None,
     if not path:
         raise Exception('you need to specify a path to search the docs on !')
 
-    return settings, path, theme, output_path, markup
+    return settings, path, theme, output_path, markup, keep
 
 
-def run_generators(generators, settings, path, theme, output_path, markup):
+def run_generators(generators, settings, path, theme, output_path, markup, keep):
     """Run the generators and return"""
 
     context = settings.copy()
-    generators = [p(context, settings, path, theme, output_path, markup) 
+    generators = [p(context, settings, path, theme, output_path, markup, keep) 
             for p in generators]
 
     for p in generators:
@@ -57,7 +58,7 @@ def run_generators(generators, settings, path, theme, output_path, markup):
             p.generate_context()
 
     # erase the directory if it is not the source
-    if output_path not in os.path.realpath(path):
+    if output_path not in os.path.realpath(path) and not keep:
         clean_output_dir(output_path)
 
     writer = Writer(output_path)
@@ -67,10 +68,10 @@ def run_generators(generators, settings, path, theme, output_path, markup):
             p.generate_output(writer)
 
 
-def run_pelican(settings, path, theme, output_path, markup):
+def run_pelican(settings, path, theme, output_path, markup, delete):
     """Run pelican with the given parameters"""
 
-    params = init_params(settings, path, theme, output_path, markup)
+    params = init_params(settings, path, theme, output_path, markup, delete)
     generators = [ArticlesGenerator, PagesGenerator, StaticGenerator]
     if params[0]['PDF_GENERATOR']:  # param[0] is settings
         processors.append(PdfGenerator)
@@ -94,10 +95,12 @@ def main():
               ' available.')
     parser.add_argument('-s', '--settings', dest='settings',
         help='the settings of the application. Default to None.')
+    parser.add_argument('-k', '--keep', action='store_true',
+        help='Keep the output directory and just update all the generated files. Default is to delete the output directory.')
     args = parser.parse_args()
     markup = [a.split()[0] for a in args.markup.split(',')]
 
-    run_pelican(args.settings, args.path, args.theme, args.output, markup)
+    run_pelican(args.settings, args.path, args.theme, args.output, markup, args.keep)
 
 
 if __name__ == '__main__':

pelican/settings.py

@@ -17,6 +17,7 @@ _DEFAULT_CONFIG = {'PATH': None,
                    'FALLBACK_ON_FS_DATE': True,
                    'CSS_FILE': 'main.css',
                    'REVERSE_ARCHIVE_ORDER': False,
+                   'KEEP_OUTPUT_DIRECTORY': False,
                   }
 
 def read_settings(filename):