File::Monitor::Delta(3p)

NAME
File::Monitor::Delta - Encapsulate a change to a file or directory

VERSION
This document describes File::Monitor::Delta version 1.00

SYNOPSIS
    use File::Monitor;

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

    # Watch some files
    for my $file (qw( myfile.txt yourfile.txt otherfile.txt some_directory )) {
        $monitor->watch( $file );
    }

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

    # After the first scan we get a list of File::Monitor::Delta objects
    # that describe any changes
    my @changes = $object->scan;

    for my $change (@changes) {
        # Call methods on File::Monitor::Delta to discover what changed
        if ($change->is_size) {
            my $name     = $change->name;
            my $old_size = $change->old_size;
            my $new_size = $change->new_size;
            print "$name has changed size from $old_size to $new_size\n";
        }
    }

DESCRIPTION
When File::Monitor or File::Monitor::Object detects a change to a file or directory it packages the details of the change in a "File::Monitor::Delta" object.

Methods exist to discover the nature of the change ("is_event" et al.), retrieve the attributes of the file or directory before and after the change ("old_mtime", "old_mode", "new_mtime", "new_mode" etc), retrieve details of the change in a convenient form ("files_created", "files_deleted") and gain access to the File::Monitor::Object for which the change was observed ("object").

Unless you are writing a subclass of "File::Monitor::Object" it isn't normally necessary to instantiate "File::Monitor::Delta" objects directly.

  Changes Classified
Various types of change are identified and classified into the following hierarchy:

    change
        created
        deleted
        metadata
            time
                mtime
                ctime
            perms
                uid
                gid
                mode
            size
        directory
            files_created
            files_deleted

The terminal nodes of that tree ("created", "deleted", "mtime", "ctime", "uid", "gid", "mode", "size", "files_created" and "files_deleted") represent actual change events. Non terminal nodes represent broader classifications of events. For example if a file's mtime changes the resulting "File::Monitor::Delta" object will return true for each of

    $delta->is_mtime;       # The actual change
    $delta->is_time;        # One of the file times changed
    $delta->is_metadata;    # The file's metadata changed
    $delta->is_change;      # This is true for any change

This event classification is used to target callbacks at specific events or categories of events. See File::Monitor and File::Monitor::Object for more information about callbacks.

  Accessors
Various accessors allow the state of the object before and after the change and the details of the change to be queried.

These accessors return information about the state of the file or directory before the detected change:

    old_dev old_inode old_mode old_num_links old_uid old_gid
    old_rdev old_size old_mtime old_ctime old_blk_size old_blocks
    old_error old_files

For example:

    my $mode_was = $delta->old_mode;

These accessors return information about the state of the file or directory after the detected change:

    new_dev new_inode new_mode new_num_links new_uid new_gid
    new_rdev new_size new_mtime new_ctime new_blk_size new_blocks
    new_error new_files

For example:

    my $new_size = $delta->new_size;

These accessors return a value that reflects the change in the corresponding attribute:

    created deleted mtime ctime uid gid mode size

With the exception of "mode", "created" and "deleted" they return the difference between the old value and the new value. This is only really useful in the case of "size":

    my $grown_by = $delta->size;

Is equivalent to

    my $grown_by = $delta->new_size - $delta->old_size;

For the other values the subtraction is performed merely to ensure that these values are non-zero.

    # Get the difference between the old and new UID. Unlikely to be
    # interesting.
    my $delta_uid = $delta->uid;

As a special case the delta value for "mode" is computed as old_mode ^ new_mode. The old mode is XORed with the new mode so that

    my $bits_changed = $delta->mode;

gets a bitmask of the mode bits that have changed.

If the detected change was the creation or deletion of a file "created" or "deleted" respectively will be true.

    if ( $delta->created ) {
        print "Yippee! We exist\n";
    }

    if ( $delta->deleted ) {
        print "Boo! We got deleted\n";
    }

For a directory which is being monitored with the "recurse" or "files" options (see File::Monitor::Object for details) "files_created" and "files_deleted" will contain respectively the list of new files below this directory and the list of files that have been deleted.

    my @new_files = $delta->files_created;

    for my $file ( @new_files ) {
        print "$file created\n";
    }

    my @gone_away = $delta->files_deletedl

    for my $file ( @gone_away ) {
        print "$file deleted\n";
    }

INTERFACE

new( $args )
    Create a new "File::Monitor::Delta" object. You don't normally need to do this; deltas are created as necessary by File::Monitor::Object.

    The single argument is a reference to a hash that must contain the following keys:

    object
        The File::Monitor::Object for which this change is being reported.

    old_info
        A hash describing the state of the file or directory before the change.

    new_info
        A hash describing the state of the file or directory after the change.

is_event( $event )
    Returns true if this delta represents the specified event. For example, if a file's size changes the following will all return true:

        $delta->is_event('size');        # The actual change
        $delta->is_event('metadata');    # The file's metadata changed
        $delta->is_event('change');      # This is true for any change

    Valid eventnames are

        change created deleted metadata time mtime ctime perms uid gid
        mode size directory files_created files_deleted

    As an alternative interface you may call "is_"eventname directly. For example

        $delta->is_size;
        $delta->is_metadata;
        $delta->is_change;

    Unless the event you wish to test for is variable this is a cleaner, less error prone interface.

    Normally your code won't see a "File::Monitor::Delta" for which "is_change" returns false. Any change causes "is_change" to be true and the "scan" methods of "File::Monitor" and "File::Monitor::Object" don't return deltas for unchanged files.

"name"
    The name of the file for which the change is being reported. Read only.

"object"
    The File::Monitor::Object for which this change is being reported.

  Other methods
As mentioned above a large number of other accessors are provided to get the state of the object before and after the change and query details of the change:

    old_dev old_inode old_mode old_num_links old_uid old_gid old_rdev
    old_size old_mtime old_ctime old_blk_size old_blocks old_error
    old_files new_dev new_inode new_mode new_num_links new_uid new_gid
    new_rdev new_size new_mtime new_ctime new_blk_size new_blocks
    new_error new_files created deleted mtime ctime uid gid mode size
    files_created files_deleted name

See "Accessors" for details of these.

DIAGNOSTICS

"%s is read-only"
    "File::Monitor::Delta" is an immutable description of a change in a file's state. None of its accessors allow values to be changed.

"You must supply a value for %s"
    The three options that "new" ("old_info", "new_info" and "object") are all mandatory.

CONFIGURATION AND ENVIRONMENT
File::Monitor::Delta 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.

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