File locking

        use Fcntl ':flock';

        my $important_file = "/etc/passwd";
        my $semaphore = "/etc/passwd.sem";

        open my($sem), "+>>", $semaphore or die ...;
        if (flock $sem, LOCK_EX) {
           # ... open the file
           # ... modify the file
           # ... close the file
        }
        close $sem;

Next

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