Check this out, and there are some similar things in c on freshmeat.net.

#!/usr/bin/perl
use POE::Component::DirWatch;

# 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. 

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