flock FILEHANDLE,OPERATION
Calls flock(2) on FILEHANDLE. See flock(2) for
definition of OPERATION. Returns TRUE for success, FALSE on failure.
Will produce a fatal error if used on a machine that doesn't implement
flock(2). Here's a mailbox appender for BSD systems.
$LOCK_SH = 1;
$LOCK_EX = 2;
$LOCK_NB = 4;
$LOCK_UN = 8;
sub lock {
flock(MBOX,$LOCK_EX);
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();
Note that flock() can't lock things over the network. You need to do
locking with fcntl() for that.
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