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IO::Async::File - watch a file for changes


   use IO::Async::File;

   use IO::Async::Loop;
   my $loop = IO::Async::Loop->new;

   my $file = IO::Async::File->new(
      filename => "config.ini",
      on_mtime_changed => sub {
         my ( $self ) = @_;
         print STDERR "Config file has changed\n";
         reload_config( $self->handle );

   $loop->add( $file );



This subclass of IO::Async::Notifier watches an open filehandle or named filesystem entity for changes in its stat() fields. It invokes various events when the values of these fields change. It is most often used to watch a file for size changes; for this task see also IO::Async::FileStream.

While called "File", it is not required that the watched filehandle be a regular file. It is possible to watch anything that stat(2) may be called on, such as directories or other filesystem entities.


The following events are invoked, either using subclass methods or CODE references in parameters.

on_dev_changed $new_dev, $old_dev

on_ino_changed $new_ino, $old_ino


on_ctime_changed $new_ctime, $old_ctime

Invoked when each of the individual stat() fields have changed. All the stat() fields are supported apart from blocks and blksize. Each is passed the new and old values of the field.

on_devino_changed $new_stat, $old_stat

Invoked when either of the dev or ino fields have changed. It is passed two File::stat instances containing the complete old and new stat() fields. This can be used to observe when a named file is renamed; it will not be observed to happen on opened filehandles.

on_stat_changed $new_stat, $old_stat

Invoked when any of the stat() fields have changed. It is passed two File::stat instances containing the old and new stat() fields.


The following named parameters may be passed to new or configure.

handle => IO

The opened filehandle to watch for stat() changes if filename is not supplied.

filename => STRING

Optional. If supplied, watches the named file rather than the filehandle given in handle. The file will be opened for reading and then watched for renames. If the file is renamed, the new filename is opened and tracked similarly after closing the previous file.

interval => NUM

Optional. The interval in seconds to poll the filehandle using stat(2) looking for size changes. A default of 2 seconds will be applied if not defined.



   $handle = $file->handle;

Returns the filehandle currently associated with the instance; either the one passed to the handle parameter, or opened from the filename parameter.


Paul Evans <>