#!/usr/bin/perl -wT
use strict;
use Fcntl qw/:flock/;
use CGI   qw/:standard/;

my $log      = 'somelog.log';
my $lockfile = "$log.lock";

# grab form data
my $_name  = param( 'name' );
my $_email = param( 'email' );

# untaint form data
my ( $name )  = ( $_name =~ /^([\w.',]{1,30})$/ )
    or some_error_routine( $_name );

# I *hate* dot-star untainting, but virtually any character
# is valid in an email address.
my ( $email ) = ( $_email =~ /^(.{1,500})$/ )
    or some_error_routine( $_name );

# We're getting rid of ASCII zero as this is the delimiter
# in the file we're writing to.
$email =~ s/\0//g;

open LOCK, "> $lockfile" or die "Cannot open $lockfile: $!";
flock LOCK, LOCK_EX      or die "Cannot flock $lockfile: $!";

open LOG, ">> $log"      or die "Can't open $log for appending: $!";
print LOG "$name\0$email\n";
close LOG;
close LOCK;

# output some response here