show dpkg version number

[534o]

$ ./rosversionall            
ROS_LOG_DIR=/home/user/.ros/log/                                                    
ROS_ETC_DIR=/opt/ros/melodic/etc/ros                       
ROS_ROOT=/opt/ros/melodic/share/ros           
ROS_MASTER_URI=http://localhost:11311                                              
ROS_VERSION=1                                                                     
ROS_PYTHON_VERSION=2                                                               
ROS_PACKAGE_PATH=/opt/ros/melodic/share               
ROSLISP_PACKAGE_DIRECTORIES=                                       
ROS_DISTRO=melodic                                                            
abseil_cpp              0.2.3   /opt/ros/melodic/share/abseil_cpp (0.2.3-1bionic.20180719.150528)
ackermann_msgs          1.0.1   /opt/ros/melodic/share/ackermann_msgs (1.0.1-0bionic.20180606.183233)
actionlib               1.11.13 /opt/ros/melodic/share/actionlib (1.11.13-0bionic.20180806.202241)
actionlib_msgs          1.12.6  /opt/ros/melodic/share/actionlib_msgs (1.12.6-0bionic.20180606.215905)