3.2.39 flock

flock 

FILEHANDLE

, 

OPERATION

This function calls flock (2) on FILEHANDLE . See the manual page for flock (2) for the definition of OPERATION . Invoking flock will produce a fatal error if used on a machine that doesn't implement flock (2) or emulate it through some other locking mechanism. Here's a mailbox appender for some BSD-based systems:

$LOCK_SH = 1; $LOCK_EX = 2; $LOCK_NB = 4; $LOCK_UN = 8;  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();

Note that flock is unlikely to work on a file being accessed through a network file system.