NAME

File::Monitor - Monitor files and directories for changes.

VERSION

This document describes File::Monitor version 0.0.1

SYNOPSIS

    use File::Monitor;

    my $monitor = File::Monitor->new();

    # Just watch
    $monitor->watch('somefile.txt');

    # Watch with callback
    $monitor->watch('otherfile.txt', sub {
        my ($name, $event, $change) = @_;
        # Do stuff
    });

    # Watch a directory
    $monitor->watch( {
        name        => 'somedir',
        recurse     => 1,
        callback    => {
            files_created => sub {
                my ($name, $event, $change) = @_;
                # Do stuff
            }
        }
    } );

    # First scan just finds out about the monitored files. No changes
    # will be reported.
    $object->scan;

    # Later perform a scan and gather any changes
    my @changes = $object->scan;

DESCRIPTION

This module provides a simple interface for monitoring one or more files or directories and reporting any changes that are made to them.

It can

• monitor existing files for changes to any of the attributes returned by the stat function

• monitor files that don't yet exist and notify you if they are created

• notify when a monitored file is deleted

• notify when files are added or removed from a directory

Some possible applications include

• monitoring the configuration file(s) of a long running process so they can be automatically re-read if they change

• implementing a 'drop box' directory that receives files to be processed in some way

• automatically rebuilding a cached object that depends on a number of files if any of those files changes

In order to monitor a single file create a new monitor object:

    my $monitor = File::Monitor->new();

Add the file to it:

    $monitor->watch( 'somefile.txt' );

And then call scan periodically to check for changes:

    my @changes = $monitor->scan;

The first call to scan will never report any changes; it captures a snapshot of the state of all monitored files and directories so that subsequent calls to scan can report any changes.

Note that File::Monitor doesn't provide asynchronous notifications of file changes; you have to call scan to learn if there have been any changes.

To monitor multiple files call watch for each of them:

    for my $file ( @files ) {
        $monitor->watch( $file );
    }

If there have been any changes scan will return a list of File::Monitor::Delta objects.

    my @changes = $monitor->scan;
    for my $change (@changes) {
        warn $change->name, " has changed\n";
    }

Consult the documentation for File::Monitor::Delta for more information.

If you prefer you may register callbacks to be triggered when changes occur.

    # Gets called for all changes
    $monitor->callback( sub {
        my ($file_name, $event, $change) = @_;
        warn "$file_name has changed\n";
    } );

    # Called when file size changes
    $monitor->callback( size => sub {
        my ($file_name, $event, $change) = @_;
        warn "$file_name has changed size\n";
    } );

See File::Monitor::Delta for more information about the various event types for which callbacks may be registered.

You may register callbacks for a specific file or directory.

    # Gets called for all changes to server.conf
    $monitor->watch( 'server.conf', sub {
        my ($file_name, $event, $change) = @_;
        warn "Config file $file_name has changed\n";
    } );

    # Gets called if the owner of server.conf changes
    $monitor->watch( {
        name        => 'server.conf',
        callback    => {
            uid => sub {
                my ($file_name, $event, $change) = @_;
                warn "$file_name has changed owner\n";
            }
        }
    } );

This last example shows the canonical way of specifying the arguments to watch as a hash reference. Any arguments passed to watch are passed unchanged to File::Monitor::Object->new; See File::Monitor::Object for more information.

Directories

When monitoring a directory you can choose to ignore its contents, scan its contents one level deep or perform a recursive scan of all its subdirectories.

See File::Monitor::Object for more information and caveats.

INTERFACE

new( %args )

Create a new File::Monitor object. Any options should be passed as a reference to a hash as follows:

    my $monitor = File::Monitor->new( {
        callback => {
            uid => sub {
                my ($file_name, $event, $change) = @_;
                warn "$file_name has changed owner\n";
            },
            size => sub {
                my ($file_name, $event, $change) = @_;
                warn "$file_name has changed size\n";
            }
    } );

The only option supported at the moment is callback which, if present, must be a reference to a hash that maps event types to handler subroutines. See File::Monitor::Delta for a full list of available event types.

set_watcher( $object )

Add a File::Monitor::Object (or compatible object) to the list of objects monitored. Replaces any existing watcher object registered for the same file or directory.

The object added must expose the methods scan and name with the same semantics as File::Monitor::Object.

watch( $name, $callback | { args } )

Create a new File::Monitor::Object and add it to this monitor. This call is a convenience shortcut for

    my $watcher = File::Monitor::Object->new( $args );
    $monitor->set_watcher( $watcher );

unwatch( $name )

Remove the watcher (if any) that corresponds with the specified file or directory.

    my $file = 'config.cfg';
    $monitor->watch( $file );       # Now we're watching it

    $monitor->unwatch( $file );     # Now we're not

scan()

Perform a scan of all monitored files and directories and return a list of changes. Any callbacks that are registered will have been triggered before scan returns.

When scan is first called the current state of the various monitored files and directories will be captured but no changes will be reported.

The return value is a list of File::Monitor::Delta objects, one for each changed file or directory.

    my @changes = $monitor->scan;

    for my $change ( @changes ) {
        warn $change->name, " changed\n";
    }

callback( [ $event, ] $coderef )

Register a callback. If $event is omitted the callback will be called for all changes. Specify $event to limit the callback to certain event types. See File::Monitor::Delta for a full list of events.

    $monitor->callback( sub {
        # called for all changes
    } );

    $monitor->callback( metadata => sub {
        # called for changes to file/directory metatdata
    } );

The callback subroutine will be called with the following arguments:

$name

The name of the file or directory that has changed.

$event

The type of change. If the callback was registered for a specific event it will be passed here. The actual event may be one of the events below the specified event in the event hierarchy. See File::Monitor::Delta for more details.

$delta

The File::Monitor::Delta object that describes this change.

DIAGNOSTICS

Watcher %s lacks the required methods: %s

You may pass any object to set_watcher that exposes methods called name and scan. The object you have passed doesn't support one or both of those methods.

This is most likely because intended to pass an instance of File::Monitor::Object but have actually passed something else.

A filename must be specified

You must pass unwatch the name of a file or directory to stop watching.

CONFIGURATION AND ENVIRONMENT

File::Monitor requires no configuration files or environment variables.

DEPENDENCIES

None.

INCOMPATIBILITIES

None reported.

BUGS AND LIMITATIONS

No bugs have been reported.

Please report any bugs or feature requests to bug-file-monitor@rt.cpan.org, or through the web interface at http://rt.cpan.org.

AUTHOR

Andy Armstrong <andy@hexten.net>

Faycal Chraibi originally registered the File::Monitor namespace and then kindly handed it to me.

LICENCE AND COPYRIGHT

Copyright (c) 2007, Andy Armstrong <andy@hexten.net>. All rights reserved.

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

DISCLAIMER OF WARRANTY

BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE SOFTWARE, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE SOFTWARE PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR CORRECTION.

IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE SOFTWARE AS PERMITTED BY THE ABOVE LICENCE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE SOFTWARE TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.