use strict;
use warnings;

use CGI;
use Getopt::Long;
use FindBin;
use Fcntl q(:flock);

use constant FILENAME => "FindBin::Bin/file.csv";

open my $self_fh, "< $0" or die "Cannot open self: $!";
flock $self_fh, LOCK_EX or die "Cannot obtain an exclusive lock: $!";

open my $infh, '<', FILENAME or die "Unable to open input file: $!";
open my $outfh, '>', FILENAME . '.out' or die "Unable to open output file: $!";

my $q = CGI->new;
chomp ( my $fqdn = $q->param('fqdn') );
chomp ( my $address = $q->param('address') );

while( <$infh> ) {
  s/RECORDNAME/$fqdn/;
  s/RECORDIP/$address/;
  print $outfh $_;
}
close $infh;
close $outfh or die "Failed to close output file: $!";

rename FILENAME . '.out', FILENAME
  or die "Unable to replace original file: $!";
  
close $self_fh or die $!;  # Releases the lock.

print "Content-type: text/plain\n\n";
print "$address / $fqdn";