Add CLI argument to print current settings

Fixes #2275
Refs #1762

docs/settings.rst

@@ -21,6 +21,12 @@ Settings are configured in the form of a Python module (a file). There is an
 <https://github.com/getpelican/pelican/raw/master/samples/pelican.conf.py>`_
 available for reference.
 
+To see a list of current settings in your environment, including both default
+and any customized values, run the following command (append a specific
+setting name as an argument to see the value for that one setting)::
+
+    pelican --print-settings
+
 All the setting identifiers must be set in all-caps, otherwise they will not be
 processed. Setting values that are numbers (5, 20, etc.), booleans (True,
 False, None, etc.), dictionaries, or tuples should *not* be enclosed in
@@ -28,10 +34,9 @@ quotation marks. All other values (i.e., strings) *must* be enclosed in
 quotation marks.
 
 Unless otherwise specified, settings that refer to paths can be either absolute
-or relative to the configuration file.
-
-The settings you define in the configuration file will be passed to the
-templates, which allows you to use your settings to add site-wide content.
+or relative to the configuration file. The settings you define in the
+configuration file will be passed to the templates, which allows you to use your
+settings to add site-wide content.
 
 Here is a list of settings for Pelican:
 

pelican/__init__.py

@@ -11,6 +11,7 @@ import re
 import sys
 import time
 import traceback
+from pprint import pprint
 
 import six
 
@@ -319,6 +320,12 @@ def parse_arguments():
                         help='Relaunch pelican each time a modification occurs'
                         ' on the content files.')
 
+    parser.add_argument('--print-settings', dest='print_settings',
+                        action='append', nargs='?', metavar='SETTING_NAME',
+                        help='Print current configuration settings and exit. '
+                        'Append a setting name as argument to see the value '
+                        'for that specific setting only.')
+
     parser.add_argument('--relative-urls', dest='relative_paths',
                         action='store_true',
                         help='Use relative urls in output, '
@@ -527,6 +534,21 @@ def main():
 
     try:
         pelican, settings = get_instance(args)
+
+        if args.print_settings:
+            # If no argument was given to --print-settings, print all settings
+            if args.print_settings[0] is None:
+                pprint(settings)
+            # An argument was given to --print-settings, so print that setting
+            else:
+                try:
+                    pprint(settings[args.print_settings[0]])
+                except KeyError:
+                    print("{} is not a recognized setting.".format(
+                          args.print_settings[0]))
+                    return 1
+            return 0
+
         readers = Readers(settings)
         reader_descs = sorted(set(['%s (%s)' %
                                    (type(r).__name__,