In this 2nd version, I put LOCK_EX in　file_put_contents($path,$txt,LOCK_EX);
The result is the same. You'll get an empty file if you run two instances at the same time.

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How to test it

(1) delete "data/test.txt"

(2) Open two terminals and execute "php read-and-write.php"

(3) See the results.

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