In CentOS to use p7zip from command line the cmd is 7za and not p7zip or 7z, I wasted some time on this as most manuals online tell you to use p7zip [options] filename.
To extract a file you would do:
7za x filename.7z
You can substitute the .7z extension with whatever archive extension you are trying to xtract e.g tar,gz,zip etc as long as its an extension that can be handled by 7zip which should be most of the common formats.