ar is a non-compressed archive format for Unix-style operating systems. It was mostly superseded by tar for general archiving use, but persists in use for specialized applications involving linkable libraries for development.
There are at least 5 different variants of the ar file format since it has never been formally standardized: AIX(big), AIX(small), Coherent, BSD, and GNU.
To list the contents of an archive, using the
$ ar tv example.a
To extract the contents of an archive:
$ ar xvo example.a