A missing ; and a bit of re-ordering was all to be done. Now it should do the job but a lot of it is implicit and not obvious to the Perl starter. So be careful when expanding on it...

#!/usr/bin/perl
 
use strict;
use warnings;
use autodie;

# usage:  perl makeconfig.pl < host-ip.csv

my $template_file_name="configtemplate.txt";

while(<>) {
        next if /^#/;
        chomp; 
        my ($ip, $hostname, $location) = split (/,/);
        my $ofile_name=$hostname . ".txt";
        
        open(TFILE, "< $template_file_name") || die "config template f
+ile $template_file_name: $!\n";
        $ofile_name = $hostname . ".txt";
        open(OFILE, "> $ofile_name") || die "output config file $ofile
+_name: $!\n";
        
        while (<TFILE>) {
                s/##location##/$location/;
                s/##hostname##/$hostname/;
                s/##ip##/$ip/;
                
                printf OFILE $_;
        }
        close OFILE;
        close TFILE;
}
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