An example of a configuration file with many commented lines is /etc/sysctl.conf. If you wanted to display the contents of the file without the commented lines, the following command may be issued.
grep -v '^#' /etc/sysctl.conf
However the resulting contents will be displayed with the remaining blank lines.
To get around this one of a couple of commands may be issued.
grep -v '^#' /etc/sysctl.conf | awk 'NF' grep -v '^#\|^$' /etc/sysctl.conf