I was looking into a lib file provided by some SDK, I need to extract lib by architecture. The first choice was the super 7-Zip which can extract almost every file on the Earth, but unfortunately files cannot be recognized by Hopper/IDA.
Here we go on OS X 10.9.
$ /usr/bin/file libXXX.a
libXXX.a: Mach-O universal binary with 3 architectures
libXXX.a (for architecture armv7): current ar archive random library
libXXX.a (for architecture armv7s): current ar archive random library
libXXX.a (for architecture i386): current ar archive random library