Perl needs to be installed on your machine to run this script.
Perl is freely available for almost every architecture and
Operating System via the Internet.
On Unix systems, you may want to modify the first line of the script
gnathtml, to explicitly tell the Operating system where Perl
is. The syntax of this line is:
Alternatively, you may run the script using the following command line:
$ perl gnathtml.pl [switches] files