How do I find out what files are in RPM package called gnupg using command line option? How do I list the contents of a package using rpm or yum command on CentOS/RHEL/Fedora/Red Hat/OpenSuse/Novell Suse Linux?

You can use rpm command (rpm command) itself to list the files inside a RPM package. rpm is a powerful Package Manager, which can be used to build, install, query, verify, update, and erase individual software packages. A package consists of an archive of files and meta-data used to install and erase the archive files.

rpm: Find out what files are in my rpm package

Use following syntax to list the files for already INSTALLED package:
rpm -ql package-name

Use following syntax to list the files for RPM package:
rpm -qlp package.rpm

Type the following command to list the files for gnupg*.rpm package file:
$ rpm -qlp rpm -qlp gnupg-1.4.5-1.i386.rpm
Sample outputs:

/usr/bin/gpg
/usr/bin/gpgsplit
/usr/bin/gpgv
/usr/bin/lspgpot
/usr/lib64/gnupg
/usr/lib64/gnupg/gpgkeys_ldap
/usr/lib64/gnupg/gpgkeys_mailto
/usr/share/doc/gnupg-1.2.6
/usr/share/doc/gnupg-1.2.6/AUTHORS
/usr/share/doc/gnupg-1.2.6/BUGS
/usr/share/doc/gnupg-1.2.6/COPYING
/usr/share/doc/gnupg-1.2.6/ChangeLog
/usr/share/doc/gnupg-1.2.6/DETAILS
/usr/share/doc/gnupg-1.2.6/HACKING
/usr/share/doc/gnupg-1.2.6/INSTALL
/usr/share/doc/gnupg-1.2.6/NEWS
....
..
...

In this example, list files in a installed package called ksh:
$ rpm -ql ksh
Sample outputs:

/bin/ksh
/bin/ksh93
/etc/kshrc
/etc/skel/.kshrc
/usr/share/doc/ksh-20120801
/usr/share/doc/ksh-20120801/COMPATIBILITY
/usr/share/doc/ksh-20120801/ChangeLog
/usr/share/doc/ksh-20120801/README
/usr/share/doc/ksh-20120801/RELEASE
/usr/share/man/man1/ksh.1.gz
/usr/share/man/man1/ksh93.1.gz

List the contents of a package using yum command

You need to install yum-utils package and use a command called repoquery to list the contents of a rpm package file:
$ repoquery -q -l --plugins ksh

/bin/ksh
/bin/ksh93
/etc/kshrc
/etc/skel/.kshrc
/usr/share/doc/ksh-20120801
/usr/share/doc/ksh-20120801/COMPATIBILITY
/usr/share/doc/ksh-20120801/ChangeLog
/usr/share/doc/ksh-20120801/README
/usr/share/doc/ksh-20120801/RELEASE
/usr/share/man/man1/ksh.1.gz
/usr/share/man/man1/ksh93.1.gz

See also

1. HowTo: Extract an RPM Package Files Without Installing It
2. rpm command cheat sheet
3. Man pages: rpm(8),yum(8),repoquery(1)