how to extract rpm packages?
 

who can tell me how to extract rpm packages? thanks first!

What exactly do you mean extract? do you mean install? or remove from your system? or view files contained in the RPM file?

rpm -i package name to install it
rpm -e package name to delete it

i want to see the files which the rpm packages contains ,such as spec file.

#rpm -i packagename.rpm (to install package)
#rpm -e packagename.rpm (to install package)

You can check the content of an rpm package with:
# rpm -qil nameofrpm.rpm
for an rpm package which is already installed
and
# rpm -qilp nameofrpm.rpm
for an rpm package which is not already installed on your system

But I don't know how you would "unpack" it without actually installing it.

i am bluiding some rpm packages,so i want to see the *.spec of some rpm packages.not install or uninstall packages.