use Fcntl qw( LOCK_EX SEEK_SET );

my $flashcount_file = '/var/www/html/log/flashcount.txt';

open(my $flashcount, '+<', $flashcount_file)
   or die;

flock($flashcount, LOCK_EX)
   or die;

my $count = <$flashcount>;
$count =~ s/^count=//;
$count++;

seek($flashcount, 0, SEEK_SET)
   or die;

# Not needed in this case.
truncate($flastcount, 0)
   or die;

print $flashcount "count=$count\n";