Some times we need control over read and write over files operation. File locking comes for rescue.
Though Perl provide many function to control over file locking operation. I found flock function is the best.
Perl monks has a great tutorial for flock and operation and usage . Simple usage and operation number and their meaning.
sub LOCK_SH { 1 } ## shared lock
sub LOCK_EX { 2 } ## exclusive lock
sub LOCK_NB { 4 } ## non-blocking
sub LOCK_UN { 8 } ## unlock
