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While using 
-R
 with 
chmod
 can save you some time, it can also cause trouble if 
you have a mix of directories and files underneath the directory you're changing 
permissions on. The previous example gives permissions 
770
 to 
mydir
 and all of its 
contents. If there are files inside, they are now given executable permissions to the 
user and group, since 
7
 includes the execute bit (value of 
1
). This may not be what 
you want. We can use the 
find
 command to differentiate these. While 
find
 is out 
of the scope of this chapter, it should be relatively simple to see what the following 
commands are doing and how they may be useful:
find /path/to/dir/ -type f -exec chmod 644 {} \; 
find /path/to/dir/ -type d -exec chmod 755 {} \; 
Basically, in the first example, the 
find
 command
 is locating all files (
-type f
) in 
/path/
to/dir/
 and everything it finds, it executes 
chmod 644
 against. The second example is 
locating all directories in this same path and changing them all to permission 
755
. The 
find
 command isn't covered in detail here because it easily deserves a chapter of its 
own, but I'm including it here because hopefully these examples are useful and will be 
handy for you to include in your own list of useful commands.