$ sh get_check_certexp
Replace the path for utils.pm with the path to the nagios plugins.
$ sed -i.bak 's#/usr/local/nagios/libexec#/usr/lib/nagios/plugins#' check_certexp.pl
Install required Perl packages.
$ apt-get install libdate-manip-perl libnet-ssleay-perl libnagios-plugin-perl