perl function flock

The flock function in Perl is used to apply advisory locks on files. It takes two arguments: the filehandle to lock and the type of lock to apply. The lock type can be either shared (LOCK_SH) or exclusive (LOCK_EX).

Here's an example of using flock to apply an exclusive lock on a file:

open(my $fh, '>>', 'filename.txt') or die "Can't open file: $!";
flock($fh, LOCK_EX) or die "Can't lock file: $!";

# write to the file
print $fh "Some text to write to the file.\n";

# release the lock
flock($fh, LOCK_UN);
close $fh;

In this example, the open function is used to open the file filename.txt in append mode. The flock function is then called with the filehandle $fh and the lock type LOCK_EX to apply an exclusive lock on the file. The print function is then used to write some text to the file while the lock is held. Finally, the flock function is called again with the filehandle $fh and the lock type LOCK_UN to release the lock, and the close function is used to close the filehandle.

Note that flock applies advisory locks, which means that it is up to the cooperating processes to respect the locks. If another process attempts to access the locked file without checking the lock first, it can still modify the file.