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

my $file = 'dogy';

open my $FH, '+<', $file or die "Cannot open '$file' $!";
flock $FH, LOCK_EX or die "Cannot flock '$file' $!";
my @newEntries = grep !($_ % 2), <$FH>;
seek $FH, 0, SEEK_SET or die "Cannot seek '$file' $!";
truncate $FH, 0 or die "Cannot truncate '$file' $!";
print $FH @newEntries;
close $FH;