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

VERSION
    This document describes File::Monitor version 1.00

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. See "watch" for more details.

  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( {
                base     => $some_dir,
                callback => {
                    uid => sub {
                        my ($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";
                    }
            } );

        Both options ("base" and "callback") are optional.

        The "base" option specifies a base directory. When a base directory
        has been specified all pathnames will internally be stored relative
        to it. This doesn't affect the public interface which still uses
        absolute paths but it does makes it possible to relocate a
        File::Monitor if the directory it's watching is moved.

        The "callback" option 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.

    "watch( $name, $callback | { args } )"
        Create a new File::Monitor::Object and add it to this monitor.

        The passed hash reference contains various options as follows:

            $monitor->watch( {
                name        => $file_or_directory_name,
                recurse     => $should_recurse_directory,
                files       => $should_read_files_in_directory,
                callback    => {
                    $some_event => sub {
                        # Handler for $some_event
                    },
                    $other_event => sub {
                        # Handler for $other_event
                    }
                }
            } );

        Here are those options in more detail:

        "name"
            The name of the file or directory to be monitored. Relative
            paths will be made absolute relative to the current directory at
            the time of the call. This option is mandatory; "new" will croak
            if it is missing.

        "recurse"
            If this is a directory and "recurse" is true monitor the entire
            directory tree below this directory.

        "files"
            If this is a directory and "files" is true monitor the files and
            directories immediately below this directory but don't recurse
            down the directory tree.

            Note that if you specify "recurse" or "files" only the *names*
            of contained files will be monitored. Changes to the contents of
            contained files are not detected.

        "callback"
            Provides a reference to a hash of callback handlers the keys of
            which are the names of events as described in
            File::Monitor::Delta.

        Callback subroutines are 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.

        As a convenience "watch" may be called with a simpler form of
        arguments:

            $monitor->watch( $name );

        is equivalent to

            $monitor->watch( {
                name    => $name
            } );

        And

            $monitor->watch( $name, $callback );

        is eqivalent to

            $monitor->watch( {
                name        => $name
                callback    => {
                    change      => $callback
                }
            } );

    "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.

    "base"
        Get or set the base directory. This allows the entire monitor tree
        to be relocated.

            # Create a monitor and watch a couple of files
            my $monitor = File::Monitor->new( { base => $some_dir } );
            $monitor->watch( "$some_dir/source.c" );
            $monitor->watch( "$some_dir/notes.text" );
    
            # Now move the directory and patch up the monitor
            rename( $some_dir, $other_dir );
            $monitor->base( $other_dir );

            # Still works
            my @changes = $monitor->scan;

        If you are going to specify a base directory you must do so before
        any watches are added.

    "has_monitors"
        Returns true if this File::Monitor has any monitors attached to it.
        Used internally to police the restriction that a base directory may
        not be set when monitors have been added.

DIAGNOSTICS
    "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.