File::CounterFile

CounterFile(3)        User Contributed Perl Documentation       CounterFile(3)



NAME
       File::CounterFile - Persistent counter class

SYNOPSIS
        use File::CounterFile;
        $c = new File::CounterFile "COUNTER", "aa00";

        $id = $c->inc;
        open(F, ">F$id");


DESCRIPTION
       This module implements a persistent counter class.  Each counter is
       represented by a separate file in the file system.  File locking is
       applied, so multiple processes might try to access the same counters at
       the same time without risk of counter destruction.

       You give the file name as the first parameter to the object constructor
       (new).  The file is created if it does not exist.

       If the file name does not start with "/" or ".", then it is interpreted
       as a file relative to $File::CounterFile::DEFAULT_DIR.  The default
       value for this variable is initialized from the environment variable
       TMPDIR, or /var/tmp is no environment variable is defined.  You may
       want to assign a different value to this variable before creating
       counters.

       If you pass a second parameter to the constructor, that sets the
       initial value for a new counter.  This parameter only takes effect when
       the file is created (i.e. it does not exist before the call).

       When you call the inc() method, you increment the counter value by one.
       When you call dec() the counter value is decrementd.  In both cases the
       new value is returned.  The dec() method only works for numerical
       counters (digits only).

       You can peek at the value of the counter (without incrementing it) by
       using the value() method.

       The counter can be locked and unlocked with the lock() and unlock()
       methods.  Incrementing and value retrieval is faster when the counter
       is locked, because we do not have to update the counter file all the
       time.  You can query whether the counter is locked with the locked()
       method.

       There is also an operator overloading interface to the
       File::CounterFile object.  This means that you might use the ++
       operator for incrementing the counter, -- operator for decrementing and
       you can interpolate counters diretly into strings.

BUGS
       It uses flock(2) to lock the counter file.  This does not work on all
       systems.  Perhaps we should use the File::Lock module?

COPYRIGHT
       Copyright (c) 1995-1998 Gisle Aas. All rights reserved.

       This library is free software; you can redistribute it and/or modify it
       under the same terms as Perl itself.

AUTHOR
       Gisle Aas <aas@sn.no>











3rd Berkeley Distribution    perl 5.005, patch 03               CounterFile(3)