1. pacman -S abs

1. pacman -S base-devel

2. As root, edit /etc/abs.conf to include your desired repositories: vim /etc/abs.conf. Remove the ! in front of the appropriate repositories, for example: REPOS=(core extra community !testing)

4.Download the Arch Build System(ABS) tree. As root, run:abs. Your ABS tree is now created under /var/abs. The above step is done once for all(run abs from time to time to update the source tree though). Next,

5.say if you want the source code of the Linux command find
1)find out which package the command find belongs to: pacman -Qo echo which find. The result is “usr/bin/find is owned by findutils 4.4.2-3”.

cp -r /var/abs/core/findutils /home/yourname/a_directory

cd /home/yourname/a_diretory
makepkg

Now you have your source code.