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I’ve finally got around to building an RSS feed for my study resource. I will update the feed as I add articles, but don’t be alarmed if the addition frequency is somewhat erratic. New stuff will come.

[ dmiessler.com/study RSS Feed ]

I’ve just posted my latest study piece. This one’s on Unix/Linux permissions.

[ Link: Unix/Linux Permissions ]

OS X’s kernel isn’t strictly Unix-based. It’s called XNU, and it’s a monolithic (non micro) hybrid of both Mach And BSD kernel components. What’s quite interesting is how many people (including myself up until a little while ago) think that OS X has a pure Unix (BSD) kernel.

But that’s not the case. In fact, XNU is actually an acronym for “X is Not Unix”.

In other words, while Apple’s marketing team loves to play the Unix card at every turn, its developers explicitly made a distinction between the OS X’s kernel and a true Unix kernel.

Wikipedia goes on to mention, however, that this distinction will become far less dramatic in the event that OS X becomes POSIX compliant in Leopard.

There is a bit of a debate in some circles about using xargs vs. the -exec {} option that’s built into find itself. To me, however, it’s not much of a debate; -exec isn’t nearly as good as xargs for what I use find for. I tend to use it to perform tasks involving many files. “Move all these files there”, “copy all those directories there”, “Delete these links.”, etc.

This is where -exec breaks down and xargs shows its superiority. When you use -exec to do the work you run a separate instance of the called program for each element of input. So if find comes up with 10,000 results, you run exec 10,000 times. With xargs, you build up the input into bundles and run them through the command as few times as possible, which is often just once. When dealing with hundreds or thousands of elements this is a big win for xargs.

That’s all nice and stuff, but you probably want to see it in action, right? Let’s run some numbers. Below is a listing of 1,668 .jpg files on my OS X system using both -exec and xargs:

# time find . -name "*.jpg" -exec ls {} \;

real    0m6.618s
user    0m1.465s
sys     0m4.396s

Hmm, that’s not bad — seven seconds for over around 1,600 files, right? Let’s try it with xargs.

# time find . -name "*.jpg" -print0 | xargs -0 ls

real    0m1.120s
user    0m0.594s
sys     0m0.527s

That's one (1) second vs seven (7) seconds. Seriously; xargs is the way to go.