#!/usr/bin/perl
use strict;
use Fcntl qw(:flock :seek);

my $stuff_from_myform = 'something to add';
my $MyFile = "$0.zzz";

open MYFILE, "+< $MyFile" or die "Cannot Open $MyFile: $!";
flock MYFILE, LOCK_EX or die "Unable to acquire exclusive lock for 
$MyFile: $!";

my @data = ( <MYFILE>, "$stuff_from_myform\n" );

shift @data while @data > 10;  #limit to 10 lines 

seek MYFILE, 0, SEEK_SET;
truncate MYFILE, 0;
print MYFILE @data;

close MYFILE;