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!!

Am glad it's working for you.

The script below addresses #1 and #3. Am unclear about #2. Where is that newline appearing? Here's the script:

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

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

my ( $template_file_name, $templateText, %hash ) = '';

for my $csvFile (@ARGV) {
    print "\nProcesing file $csvFile ...\n";
    open my $csvfh, '<', $csvFile or die "Unable to open $csvFile: $!"
+;

    # Ignore column names in first line
    my $columnNames = <$csvfh>;

    # Get vars from second line
    chomp( my $vars = <$csvfh> );
    my @vars = split /,/, $vars;

    while (<$csvfh>) {
        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 = $hash{'##rtrname##'} . '.txt';

        print "Writing to file: $ofile_name\n";
        open my $fh, '>', $ofile_name or die "$ofile_name: $!";
        print $fh $templateTextCopy;
        close $fh;
    }

    close $csvfh;
}

print "\nDone!\n";

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

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

    return $templateText;
}
[download]

You deserve a medal! That works perfectly!
The problem with #2 is;
If i open the .CSV in MS Excel, make a change and save it, then when i run the .pl, i get the following error:

Use of uninitialized value $vars in chomp at create-configs.pl line 18
+, <$csvfh> line 1.
Use of uninitialized value $vars in split at create-configs.pl line 19
+, <$csvfh> line 1.
[download]

However, if i open the .CSV in excel, make the changes, then open it with something like Text Edit, and go to the end of each line in the CSV, and press delete, then enter (to put evreything back to its own line), then when I run the .pl it works perfectly..
Does that make sense? if not, let me know, and I will try and send you the files if possible, so you can know what i mean..
Once again, your help is invaluable..