use 5.004;
           use Fcntl qw(:DEFAULT :flock);
           sysopen(FH, "filename", O_WRONLY | O_CREAT)
               or die "can't open filename: $!";
           flock(FH, LOCK_EX)
               or die "can't lock filename: $!";
           truncate(FH, 0)
               or die "can't truncate filename: $!";

           # now write to FH
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