| File::Monitor::Delta(3pm) | User Contributed Perl Documentation | File::Monitor::Delta(3pm) |
File::Monitor::Delta - Encapsulate a change to a file or directory
This document describes File::Monitor::Delta version 1.00
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";
}
}
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.
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.
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";
}
The single argument is a reference to a hash that must contain the following keys:
$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.
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.
File::Monitor::Delta requires no configuration files or environment variables.
None.
None reported.
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>.
Andy Armstrong "<andy@hexten.net>"
Faycal Chraibi originally registered the File::Monitor namespace and then kindly handed it to me.
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.
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| 2015-05-06 | perl v5.20.2 |