Mac OS X Leopard - ARCAism

CHAPTER 18 INTRODUCING DARWIN AND THE SHELL 307
both types of code in your application. lipo allows you to take a universal application and
“thin” it so that the resulting application will only run on one architecture. The advantage of this
is that you can free up significant amounts of space on your hard drive by thinning your application.
For example, if we delve into Sherlock.app (which in Darwin will appear as a directory,
since most OS X applications are actually application bundles, or special directories containing
all the pieces of the application) to the actual executable (/Applications/Sherlock.app/Contents/
MacOS/Sherlock), we can see that its default size is 570 KB. If we run lipo using the -thin i386
option (since I’m using an Intel machine—if you are on a PowerPC computer, you would replace
the i386 with ppc), we can shrink this file down to around 280 KB. That’s a 50 percent savings of
disk space by stripping away parts I don’t need and will never use on this computer! lipo will
thin a file by taking the initial universal binary executable, followed by the thin option, followed
by the output option and the name of the output file. lipo always makes a copy of the original,
and it’s not a bad idea to back up the original file until you are sure that the thinned file works
without error. An example of running lipo on Sherlock could look something like this:
Leopard:~ scott$ cd /Applications/Sherlock.app/Contents/MacOS/
Leopard:/Applications/Sherlock.app/Contents/MacOS scott$ ls
Sherlock*
Leopard:/Applications/Sherlock.app/Contents/MacOS scott$ du -hsk Sh*
572K Sherlock
Leopard:/Applications/Sherlock.app/Contents/MacOS scott$ lipo Sherlock -thin i386 ➥
-output Sherlock.i386
Leopard:/Applications/Sherlock.app/Contents/MacOS scott$ du -hsk Sh*
572K Sherlock
284K Sherlock.i386
Leopard:/Applications/Sherlock.app/Contents/MacOS scott$ mv Sherlock ~/Documents/
Leopard:/Applications/Sherlock.app/Contents/MacOS scott$ mv Sherlock.i386 Sherlock
NOTE The du command is a simple “disk usage” command. When used with the -hsk option,
it will simply show you how big a file or directory is from the command line.
Now I can run Sherlock to make sure everything works, and once I verify that it in fact does,
I can run rm on the original Sherlock executable and gain back close to 300 KB of my precious
disk space.
NOTE What happens if something goes wrong? Well, that’s why we back up the original,
which we can then just put back in place with no ill effect at all. By design, this should work
without issue—however, as companies transition from PowerPC-only applications to universal
applications, it’s prudent to expect that somewhere, somehow, it’s possible that something
important could get lost in this process. It’s never happened to me, but it’s better to be safe
than sorry.
NOTE lipo is actually used to create and get information about universal binaries, not to
break them apart. The use of lipo to thin out universal binaries is more of a useful side effect
than an intention.
Pipes, Redirection, and Background Tasks
A few more things we should cover before we move on are the ability to pipe one command into
another, the ability to redirect output (or input) to and from a command, and the ability to run
tasks in the background. We’ve actually done each of these things in some of the preceding
examples, yet as they are quite powerful tools, I’ll give a bit more depth here.