Take a look at the module POE::Component::DirWatch on CPAN, I think this might be what you are looking for. It watches a directory for files, and once a filename matching the filter is found, it will kick off a sub-process and invokes the given user callback.

Sample code pulled straight from the doco:

use POE::Component::DirWatch;

POE::Component::DirWatch->spawn(
    Alias        => 'dirwatch',
    Directory    => '/some_dir',
    Filter       => sub { $_[0] =~ /\.gz$/ && -f $_[1] },
    Callback     => \&some_sub,
    PollInterval => 1,
  );
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