Thanks Kenosis!! Your help is invaluable.. Ok my .pl as it stands is as follows;

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

$ARGV[0] or die "Usage: $0 <filename> [<filename>] ...";

my ( $template_file_name, $templateText, %hash ) = '';
my @vars = split "\n", <<END;
##location##
##rtrname##
##loop0-ip##
##ospf-id##
##ospf-area##
##ospf-network##
##ospf-mask##
##eth00-ip##
##eth00-sm##
END

while (<>) {
    chomp;
    my @fields     = split /,/;
    my $templateFN = pop @fields;

    if ( $template_file_name ne $templateFN ) {
        $template_file_name = $templateFN;
        undef $templateText;
    }

    @hash{@vars} = @fields;

    $templateText //= getTemplateText($template_file_name);
    my $templateTextCopy = $templateText;

    $templateTextCopy =~ s/$_/$hash{$_}/g for keys %hash;

    my $ofile_name = './Config_Output/' . $hash{'##rtrname##'} . '.txt
+';

    open my $fh, '>', $ofile_name or die "$ofile_name: $!";
    print $fh $templateTextCopy;
    close $fh;
}

sub getTemplateText {
    my ($template_file_name) = @_;

    local $/;
    open my $fh, '<', './Templates/' . $template_file_name . '.txt' or
+ die "$template_file_name: $!";
    $templateText = <$fh>;
    close $fh;

    return $templateText;
}
[download]

I still have a couple of problems, I was hoping you may be able to help with..
1. Is there a way that I can ignore the first line of the CSV? - In the CSV the first line is just column descriptions, and is not needed for the output..
2. I can still not seem to strip the newline off the end of the CSV.. I have tried to replace chomp

with

but that doesn't seem to do it.. unfortunately the csv needs to be edited with MS Excel, so when saving that, it adds its extra MS stuff to the file
3. Even better - but i don't know if this is even possible.. would there be a way, so that rather than specifying all the template variables (i.e. ##eth00-ip##, ##location## etc), I could have them all listed on the second line of the CSV, and then the code can draw those values out...?

I really appreciate your assistance, and will definitely have to buy you a beer!!