Hi

This is not like locking the file when the Othere program tries to modify the file.

Please see the below definition

      LOCK_SH   Place a shared lock.  More than one process may hold a
                        shared lock for a given file at a given time.
 
              LOCK_EX   Place an exclusive lock.  Only one process may
+ hold an
                        exclusive lock for a given file at a given tim
+e.
 
              LOCK_UN   Remove an existing lock held by this process.
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The possible ways of checking the locks :-

Having a ENVIRONMENT Variable that will check for the locking Mechanism. ( Set and Unset the Variable )

Lock file Mechanism