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Man Pages


Manual Reference Pages  -  FILE::MONITOR (3)

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NAME

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

CONTENTS

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
o monitor existing files for changes to any of the attributes
returned by the stat function
o monitor files that don’t yet exist and notify you if they
are created
o notify when a monitored file is deleted
o notify when files are added or removed from a directory
Some possible applications include
o monitoring the configuration file(s) of a long running process
so they can be automatically re-read if they change
o implementing a ’drop box’ directory that receives files to be
processed in some way
o 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 were watching it

    $monitor->unwatch( $file );     # Now were 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.

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