find . -type d -exec chmod 0755 {} \;
find . -type f -exec chmod 0644 {} \;
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#!/usr/bin/perl -w
use strict;
use File::Find;                                                       
+                        

find(
  { wanted => sub{ chmod((-f)?0644:0755,$_) if -d||-f } 
  }, defined $ARGV[0] ? $ARGV[0] : '.'
);
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UPDATE: just had a privmsg discussion regarding this snippet and it looks that some people seem to be missing the point - goldclaw's reply is doing a DIFFERENT thing from my original goal. He somehow explained in his reply that files get chmod-ed to 0755 "if it has one or more execution bits allready set", but that's not my intention (i.e. remember Apache and XBitHack and you'll see why).
I really hope this update will clarify this missleading issue, as I see many users using chmod's X flag without perfectly understanding what's its functionality.