Perform writing operation on x file by two perl scripts at the same time.

Please let me know what will happen?

What exactly will happen depends on how (and when) you open the file, how you write to it, where you write in the file, in which order you write, when you close the file, if and when you flush, if and when the library flushes, the phase of the moon, the current price of Brent Crude, and the number of airborne butterflies in Buenos Aires.