Allow running calibre in debug mode via an environment variable

src/calibre/constants.py

@@ -87,7 +87,7 @@ else:
         filesystem_encoding = 'utf-8'
 
 
-DEBUG = False
+DEBUG = b'CALIBRE_DEBUG' in os.environ
 
 
 def debug():

src/calibre/debug.py

@@ -250,7 +250,6 @@ def main(args=sys.argv):
     opts, args = option_parser().parse_args(args)
     if opts.gui:
         from calibre.gui_launch import calibre
-        print_basic_debug_info()
         calibre(['calibre'])
     elif opts.gui_debug is not None:
         run_debug_gui(opts.gui_debug)

src/calibre/gui_launch.py

@@ -63,6 +63,10 @@ def register_with_default_programs():
 
 
 def calibre(args=sys.argv):
+    from calibre.constants import DEBUG
+    if DEBUG:
+        from calibre.debug import print_basic_debug_info
+        print_basic_debug_info()
     detach_gui()
     init_dbus()
     with register_with_default_programs():