Backing up and restoring installed software

Task: Backup list of installed software

Debian Linux
If you are using Debian Linux use dpkg command to list installed software:
$ dpkg --get-selections

Store list of installed software to a file called /backup/installed-software.log
$ dpkg --get-selections > /backup/installed-software.log

RPM based distributions (RHEL, Fedora Core, Cent OS, Suse Linux etc)
Use rpm command to get list of all installed software:
$ rpm -qa
OR
$ rpm -qa > /backup/installed-software.log

Task: Restore installed software from backup list

Now you have a list of installed software. After installing base system you can immediately install all software.

Debian Linux
Debian Linux makes your life easy. All you have to do is type following two commands:
# dpkg --set-selections < /backup/installed-software.log
Now your list is imported use dselect or other tools to install the package.
# dselect

Select ‘i‘ for install the software.

RPM based distro
As far as I know RPM based distro does not offers dpkg kind of facility. But with little shell scripting technquie you can easily install all software:
# LIST="$( cat /backup/installed-software.log )"

If you are using yum, type the following for loop to install all software:
# for s in $LIST; do yum install $s; done
Update try out following command (thanks to gt):
# yum -y install $(cat /backup/installed-software.log)

OR if you are using RHEL (RHN subscriber) :
# for s in $LIST; do up2date -i $s; done

Alternatively you use following command:
# up2date -i $(cat /backup/installed-software.log)