[root@xsi Documents]# od -c .
od: .: read error: Is a directory
0000000
I read the book about shell (Kernighan, Pike) and some exaples (like this) does not work.
I read this book carefully (because I think now quickly) even reread to better understand.
In this book there is a good example how to see what a catalog looks like.
But on my Linux system (Fedora 12) it does not seem to work at all.
Also "chmod -w file" does not work for all users. --w--w--w- (only --w--------) but for x and r work good.
Of the systems on which I tried to use od with a directory, Solaris 10 failed, but (some versions of) IBM AIX, and HP-UX succeeded.
The K & R book was written a long time ago, before Linux was created. I do not know why Linux restricts commands like cat and od from dealing with directories.
The chmod behavior might be explained by the setting of your umask. See man umask for details ... cheers, drl