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# 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();

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