How to merge two “ar” static libraries into one?

Question

I have 2 static Linux libraries, created by ar cr, libabc.a and libxyz.a.
I want to merge them into one static library libaz

Answer 1

ar -x libx264.a
mkdir sub && cd sub
ar -m ../libx264.a `ar -t ../libx264.a |sort|uniq|grep "\.o"`
ar -x ../libx264.a

now you have two version of "macroblock-10.o"