PERL flock Function

Syntax

flock FILEHANDLE, OPERATION

Definition and Usage

Supports file locking on the specified FILEHANDLE using the system flock( ), fcntl( ) locking, or lockf( ). The exact implementation used is dependent on what your system supports. OPERATION is one of the static values defined here...

Operation	Result
LOCK_SH 	Set shared lock.
LOCK_EX 	Set exclusive lock.
LOCK_UN 	Unlock specified file.
LONG_NB 	Set lock without blocking.

Return Value

0 on failure to set/unset lock
1 on success to set/unset lock

Example

Following are the usage...

Here's a mailbox appender for BSD systems:

use Fcntl ':flock'; # import LOCK_* constants

    sub lock {
	flock(MBOX,LOCK_EX);
	# and, in case someone appended
	# while we were waiting...
	seek(MBOX, 0, 2);
    }
    sub unlock {
	flock(MBOX,LOCK_UN);
    }
    open(MBOX, ">>/usr/spool/mail/$ENV{'USER'}")
	    or die "Can't open mailbox: $!";
    lock();
    print MBOX $msg,"\n\n";
    unlock();