ubuntu@ubuntu-14:~$ uname -a
Linux ubuntu-14 3.13.0-32-generic
ubuntu@ubuntu-14:~$ sudo apt-get install apt-file
ubuntu@ubuntu-14:~$ apt-file update
ubuntu@ubuntu-14:~$ apt-file search /bin/echo
9base: /usr/lib/plan9/bin/echo
alsa-tools-gui: /usr/bin/echomixer
coreutils: /bin/echo
dcmtk: /usr/bin/echoscu
echoping: /usr/bin/echoping
libbonobo2-bin: /usr/bin/echo-client-2
supervisor: /usr/bin/echo_supervisord_conf
ubuntu@ubuntu-14:~$ apt-get source coreutils
ubuntu@ubuntu-14:~$ ls -l ./coreutils-8.21/src/echo.c
-rw-rw-r-- 1 ubuntu ubuntu 7630 1月 31 2013 ./coreutils-8.21/src/echo.c