README.org

* My ArchLinux packages list
As [[https://wiki.archlinux.org/index.php/Pacman_Tips#Backing_up_and_retrieving_a_list_of_installed_packages][ArchWiki]] said, it's good to back up all the pacman-installed packages at ArchLinux.

The common practice is back up the package list in a plain text file and use pacman to re-install the packages from that file.

So the key problem is where to place the list?

My answer is that [[http://github.com][github]] is a good place to go, because:
1. github's UI is good. For example, I can download the latest snapshot in a zip file through browser.
2. Since you use git. you have copies of everything (commit history included) on both local computer and server.
3. Git is powerful. For example, I can search and restore to any older version in a blink.
* The solution
Here is the bash function "backup_archlinux_packages_list" to do these jobs.

#+BEGIN_SRC sh
# backup packages
# @see https://wiki.archlinux.org/index.php/Pacman_Tips#Backing_up_and_retrieving_a_list_of_installed_packages
# @param GITHUB_USR optional, the user name of github.com. If empty, only local backup
function backup_archlinux_packages_list() {
   mkdir -p $HOME/archlinux
   comm -23 <(pacman -Qeq|sort) <(pacman -Qmq|sort) > $HOME/archlinux/pkglist.txt
   if [ ! -e $HOME/archlinux/README.org ]; then
      echo "* My ArchLinux packages list " > $HOME/archlinux/README.org
   fi
   local GIT=`/usr/bin/which git`
   local GITHUB_USR=$1 #first parameter, optional

   if [ "${GIT}x" = "x" ]; then
      echo Git not found! You need to install git first.
      return 0
   fi

   cd $HOME/archlinux
   if [ ! -d $HOME/archlinux/.git ]; then
      #first import
      $GIT init
      $GIT add $HOME/archlinux/pkglist.txt $HOME/archlinux/README*
      $GIT commit -m 'first import'
      if [ ! "${GITHUB_USR}x" = "x" ]; then
         $GIT remote add origin "git@github.com:${GITHUB_USR}/archlinux-${HOSTNAME}.git"
         $GIT push -u origin master
      fi
   else
      # normal commit
      local gd=`${GIT} diff .`
      if [ ! "${gd}x" == "x" ]; then
         # only add files already under track
         $GIT add -u .
         $GIT commit -m `date +%H%M%S-%Y-%m-%d`
         if [ ! "${GITHUB_USR}x" = "x" ]; then
            $GIT push origin master
         fi
      fi
   fi
   cd $HOME
   return 0
}
#+END_SRC

I place the function in ~/.bashrc:
#+BEGIN_SRC sh
if [ -e /usr/bin/pacman ]; then
   backup_archlinux_packages_list my_github_usr
fi
#+END_SRC

Please note if the parameter for "backup_archlinux_packages_list" is empty. The git will only back up the data in local machine.