gistfile1.pl

use strict;                                                                
use warnings;                                                              
use POE qw( Sugar::Args );                                                 
use File::Modified;                                                        
use Perl6::Say;                                                            
                                                                           
my ($command, @files) = @ARGV;                                             
                                                                           
my $watcher = File::Modified->new(                                         
    method => 'mtime',                                                     
    files  => \@files,                                                     
);                                                                         
                                                                           
POE::Session->create(                                                      
    inline_states => {                                                     
        _start => sub {                                                    
            my $poe = sweet_args;                                          
            $poe->kernel->yield('watch');                                  
        },                                                                 
        watch  => sub {                                                    
            my $poe = sweet_args;                                          
            my @changes;                                                   
            eval { @changes = $watcher->changed };                         
            say STDERR "$_ is changed." for @changes;                      
            if (@changes) {                                                
                $watcher->update;                                          
                system($command);                                          
            }                                                              
            $poe->kernel->delay(watch => 1);                               
        },                                                                 
    },                                                                     
);                                                                         
                                                                           
POE::Kernel->sig( INT => sub { POE::Kernel->stop } );                      
POE::Kernel->run;