I know this is old but I wish to propose a more comprehensive solution.

The way I do it utilises the same idea and proposed in archlinux.org site.

• First you need the list of packages, this can be done with

  pacman -Qqe > pkglist.txt
  

  Here pacman -Q queries all installed programs, the -q removes version numbers and the -e is for listing the explicitly installed programs.

• Now, when we want to restore/install the programs, I prefer doing

  installable_packages=$(comm -12 <(pacman -Slq | sort) <(sort pkglist.txt))
  pacman -S --needed $installable_packages
  

  Here we only get the packages from the list are available from pacman. That is done with the comm -12 file1 file2 command. The -12 flag suppresses unique lines in file 1 and 2 and leaves us with the intersection of the two files; i.e., the installable packages.

Just do:

$ sudo sh -c 'cat input_file | cut "-d " -f1 |  xargs pacman -S'

or a simpler version:

$ awk '{print $1}'  input_file |  xargs pacman -S

or

$ sudo pacman -S $(awk '{print $1}'  input_file)

Where input_file contains all your packages to be installed, one to a line.

Word of caution:
As you undoubtedly know, Archlinux is a rolling release package, so specifying version to be installed is not recommended and means you could actually break dependencies and, ultimately, your system overall. For that reason alone I cut away the version info in your package records in input_file...

If you insists on a rolled back (i.e. "old") version of some package, you can roll back on Arch Linux, but I recommend you do that by hand, not in an automated way, only if you know exactly what you are getting into.

HTH.